Introduction to Python - Running Notes

PYTHON
INTRODUCTION
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summary of the contents of the document. Type the abstract of the
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Reference:
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PYTHON
Table of Contents
Python Introduction............................................................................................................................6
Python versions..............................................................................................................................6
Python console...............................................................................................................................6
Python functions ................................................................................................................................6
Python errors.....................................................................................................................................6
Python floats......................................................................................................................................7
Python numerical operations ..............................................................................................................7
__main__...........................................................................................................................................8
Command line arguments...................................................................................................................8
sys module.....................................................................................................................................8
getopt module................................................................................................................................9
getopt.getopt method.................................................................................................................9
Exception getopt.GetoptError......................................................................................................9
Example.................................................................................................................................10
Strings..............................................................................................................................................11
String formatting..........................................................................................................................11
String operations ..........................................................................................................................12
Variables..........................................................................................................................................12
Variable names:............................................................................................................................12
del statement...............................................................................................................................13
Special operators..............................................................................................................................13
if statements....................................................................................................................................13
elif (short form of else if)...............................................................................................................13
Boolean logic................................................................................................................................14
While loops......................................................................................................................................14
infinite loop..................................................................................................................................14
break...........................................................................................................................................14
continue.......................................................................................................................................14

operator precedence........................................................................................................................14
More on else statements ..................................................................................................................15
Else with loops..............................................................................................................................15
Else with try/except......................................................................................................................15
Lists.................................................................................................................................................15
Empty list.....................................................................................................................................16
Nested lists...................................................................................................................................16
Errors...........................................................................................................................................16
List operations..............................................................................................................................16
Assignment...............................................................................................................................16
Addition and Multiplication........................................................................................................16
in operator................................................................................................................................16
not operator.............................................................................................................................17
Loops........................................................................................................................................17
List slices......................................................................................................................................17
Negative indexing......................................................................................................................17
List comprehensions .....................................................................................................................18
List functions................................................................................................................................18
Sets.................................................................................................................................................19
Mathematical operations - union/intersection................................................................................19
Functions and modules.....................................................................................................................20
Arguments ...................................................................................................................................20
Return values ...............................................................................................................................21
Docstrings ....................................................................................................................................21
Modules.......................................................................................................................................21
Import certain functions............................................................................................................21
Standard Library...............................................................................................................................21
Exception Handling...........................................................................................................................22
Raising exception..........................................................................................................................23
Assertions........................................................................................................................................23
Files handling...................................................................................................................................23
Opening files - open()....................................................................................................................23

Reading Files - read().....................................................................................................................24
Writing Files - write().....................................................................................................................24
with statement.............................................................................................................................24
None................................................................................................................................................25
Dictionaries......................................................................................................................................25
Dictionary Functions .....................................................................................................................26
Search......................................................................................................................................26
get() .........................................................................................................................................26
Tuples..............................................................................................................................................26
Tuple unpacking...........................................................................................................................26
Variable*......................................................................................................................................27
Ternary operator..............................................................................................................................27
Higher order functions......................................................................................................................27
Lambdas.......................................................................................................................................27
map and filter...............................................................................................................................28
Generators.......................................................................................................................................28
Decorators.......................................................................................................................................29
Object Oriented Programming...........................................................................................................30
Classes.........................................................................................................................................30
__init__........................................................................................................................................30
Methods ......................................................................................................................................30
Inheritance...................................................................................................................................30
Super function..............................................................................................................................31
Magic Methods.............................................................................................................................31
Operator overloading....................................................................................................................31
Object Lifecycle ............................................................................................................................31
Garbage collection........................................................................................................................32
Data Hiding..................................................................................................................................32
Class methods ..............................................................................................................................32
Static methods..........................................................................................................................32
Properties ....................................................................................................................................33
Regular Expressions..........................................................................................................................34

Matching pattern..........................................................................................................................34
re.search()....................................................................................................................................34
re.sub() - search & replace.............................................................................................................35
Metacharacters ............................................................................................................................35
. (dot) character........................................................................................................................35
^ and $ - start and end...............................................................................................................35
Character classes..........................................................................................................................35
^ character................................................................................................................................36
More Metacharacters ...................................................................................................................36
* character................................................................................................................................36
+ character................................................................................................................................36
? character................................................................................................................................36
Curly braces..............................................................................................................................36
Groups.........................................................................................................................................36
| character................................................................................................................................37
Named groups...........................................................................................................................37
Special Sequences ............................................................................................................................37
number - Backslash .....................................................................................................................37
d and D sequence.......................................................................................................................38
s and S sequence........................................................................................................................38
w and W sequence.....................................................................................................................38
A Sequence.................................................................................................................................38
b sequence .................................................................................................................................38
Email extraction ...............................................................................................................................38
Pythonicness & Packaging.................................................................................................................39
PEP- Python Enhancement Proposals.................................................................................................39
Packaging.........................................................................................................................................39
Setup.py.......................................................................................................................................40
Packaging for Users.......................................................................................................................40
Function arguments..........................................................................................................................40
*args............................................................................................................................................40
**kwargs – keyword arguments ....................................................................................................41

Major 3rd
party libraries ....................................................................................................................41
Django.........................................................................................................................................41
CherryPy and Flask........................................................................................................................41
BeautifulSoup...............................................................................................................................41
Matplotlib....................................................................................................................................41
NumPy.........................................................................................................................................41
SciPy............................................................................................................................................42
Panda3D ......................................................................................................................................42
List Vs Dictionary Vs TuplesVs Sets....................................................................................................42
itertools - standard library.................................................................................................................43
Python Vs C......................................................................................................................................43
Web scraping: webbrowser library ....................................................................................................44
Webbrowser.open()......................................................................................................................44
webbrowser.open_new(url)..........................................................................................................44
webbrowser.open_new_tab(url) ...................................................................................................44
webbrowser.get([name])...............................................................................................................44

Python !!!
PythonIntroduction
Pythonisa highlevel programminglanguagelikeC/C++/Javaetc.,itsapplicationsincludingweb
programming,scripting,scientificcomputingandartificial intelligence.
pythonisprocessedatruntime bythe interpreter.Noneedto compile pythonprogramsbefore
executingthemunlikeCprograms,where compilationstepismandatorybeforeexecutingit.
An Interpreterisaprogramthat runs scriptswritteninan interpretedlanguage suchasPython.
Pythonsource fileshave anextensionof .py
Python versions
There are three majorversionsof pythonwhichare 1.x,2.x and3.x. Both2.x and 3.x are currentlyused.
Python console
The pythonconsole isa program that allowsyouto enterone line of pythoncode,repeatedlyexecutes
that line,anddisplaysthe output.Thisisknownasa REPL - Read-Eval-Print-Loop.
To close a console,type inquit() orexit() andpressenter.
Pythonfunctions
Pythonfunction Usage
print("Hello") orprint('Hello') Printsthe message,producesthe output
quit() orexit() Close the console
input("Entersomethingplease:") Promptsthe use for input,andreturnswhatthey
enteras a stringwithcontentsautomatically
escaped.
Enter somethingplease:userentersncharacter!
o/p-> userentersncharacter!
int() Convertsgivennumberinstringformattointeger
int("2") + int("3") = 5
Similarlyfloat() andstr()
del variable_name del statementusedtoremove avariable from
program.
Pythonerrors
Type of error Example
ZeroDivisionError:divisionbyzero 11 / 0
TypeError:unsupportedoperandtype(s) 1 + "2"

For +:'int' and 'str'
TypeError:can't multiplysequence bynon-intof
type 'str' or 'float'
"s" * "s"
9.0 * "r"
SyntaxError:invalidsyntax >>>123abc = 7
1. When variable namesdon'tfollowrules.
2. When programuses++ or -- operators.
NameError:name 'var_name" is notdefined Whenprogram triestoaccess undefinedvariable
or a functionwhichisnotdefined
In Lists:
IndexError:
whentry toaccess out of boundvalues.
things="hai"
print(things[4])
In Lists:
TypeError:
whentry toaccess integerorfloat typesusing
index.
Num= 123
print(Num(2))
In Lists:
ValueError:
If the itemisnotin the listand tryingto getits
index.
ImportError Whentryingto access unavailablemodule
KeyError Tryingto index akeythat isn'tpart of the
dictionaryreturnsaKeyError.
Dictionary'sTypeError Whenmutable objectsare usedaskeys
RuntimeError:maximumrecursiondepth
exceeded
Oftenoccur whenforgottoimplementthe base
case of resusion.
AttributeError Tryingto access an attribute of an instance the
isn'tdefinedcausesthiserror.
Pythonfloats
A floatcan be addedto an integerbecause Pythonsilentlyconvertsthe integertoa float.However,this
implicitconversionisthe exceptionratherthanthe rule inPython.Youhave to convertvaluesmanually
if you wantto operate onthem.
Pythonnumerical operations
Operator Usage
+ , - , * , / Addition,subtraction,multiplication,division
1 + 2 = 3
1 + 2.2 = 3.2
2 * 3 = 6
2 * 3.2 = 6.4
4/2 = 2.0
5/2 = 2.5
** Exponentiation
2**5 = 32
9**(1/2) = 3.0
// Quotient(Floordivision)

20//6 = 3
% Remainder(modulooperator)
1.25%0.5 = 0.25
Inplace operators
+= , -=, *=, %= and /=
a += 3 -> a = a + 3
__main__
Whena pythoninterpreterreadsasource file,itexecutesall of the code itfindsinthe file. Before
executingthe code,itdefinesafewspecial variables.
For example,if the pythoninterpreterisrunningthatmodule (source file) asthe mainprogram, itsets
the special __name__ variable tohave avalue “__main__”. If the file beingimportedfromanother
module, __name__ will be settothe module’sname.
If __name__ == “__main__”:
print(“Thisisascript”)
else
print(“Imported”)
Commandline arguments
sys module
The Python sys module providesaccesstoany command-lineargumentsviathe sys.argv.Thisserves
twopurposes−
 sys.argvisthe listof command-linearguments.
 len(sys.argv) isthe numberof command-linearguments.
Here sys.argv[0] isthe program ie.scriptname.
Consider the following script test.py −
#!/usr/bin/python
import sys
print 'Number of arguments:', len(sys.argv), 'arguments.'
print 'Argument List:', str(sys.argv)
Now run above script as follows −

$ python test.py arg1 arg2 arg3
This produce following result −
Number of arguments: 4 arguments.
Argument List: ['test.py', 'arg1', 'arg2', 'arg3']
getopt module
Pythonprovidesagetoptmodule thathelpsyouparse command-lineoptionsandarguments.
Pythonprovidedagetoptmodule thathelpsyouparse command-lineoptionsandarguments.This
module providestwofunctionsandan exceptiontoenablecommandline argumentparsing.
getopt.getoptmethod
Thismethodparsescommandline optionsandparameterlist.Followingissimple syntaxforthismethod
−
getopt.getopt(args,options,[long_options])
Here is the detail of the parameters−
 args: Thisisthe argumentlistto be parsed.
 options:This isthe stringof optionlettersthatthe scriptwantsto recognize,withoptionsthat
require anargumentshouldbe followedbyacolon(:).
 long_options:Thisis optional parameterandif specified,mustbe alistof stringswiththe
namesof the longoptions,whichshouldbe supported.Longoptions,whichrequire an
argumentshouldbe followedbyanequal sign('=').To accept onlylongoptions,optionsshould
be an emptystring.
 Thismethodreturnsvalue consistingof twoelements:the firstisalistof (option,value) pairs.
The secondis the listof program argumentsleftafterthe optionlistwasstripped.
 Each option-and-valuepairreturnedhasthe optionasitsfirstelement,prefixed withahyphen
for shortoptions(e.g.,'-x') ortwohyphensforlongoptions(e.g.,'--long-option').
Exceptiongetopt.GetoptError
Thisis raisedwhenanunrecognizedoptionisfoundinthe argumentlistorwhenanoptionrequiringan
argumentisgivennone.
The argumentto the exceptionisastringindicatingthe cause of the error. The attributesmsgandopt
give the errormessage andrelatedoption.

Example
Consider we want to pass two file names through command line and we
also want to give an option to check the usage of the script. Usage of the
script is as follows −
usage: test.py -i <inputfile> -o <outputfile>
Here is the following script to test.py −
#!/usr/bin/python
import sys, getopt
def main(argv):
inputfile = ''
outputfile = ''
try:
opts, args = getopt.getopt(argv,"hi:o:",["ifile=","ofile="])
except getopt.GetoptError:
print 'test.py -i <inputfile> -o <outputfile>'
sys.exit(2)
for opt, arg in opts:
if opt == '-h':
print 'test.py -i <inputfile> -o <outputfile>'
sys.exit()
elif opt in ("-i", "--ifile"):
inputfile = arg
elif opt in ("-o", "--ofile"):
outputfile = arg
print 'Input file is "', inputfile
print 'Output file is "', outputfile
if __name__ == "__main__":
main(sys.argv[1:])

Now, run above script as follows −
$ test.py -h
$ test.py -i BMP -o
$ test.py -i inputfile
Input file is " inputfile
Output file is "
Strings
A stringiscreatedby enteringtextbetweentwosingle ordouble quotationmarks.
-> 'HelloWorld'or "HelloWorld"
Some characters can't be includedinstringdirectly,example of these charactersare single quoteand
double quotes,tabs, arbitraryunicode characters.
Put a backslashbefore these charactersif youaddthese special charactersinyourstring.
"Ram's brothername is "Raj""-->Ram's brothername is Raj
n - representsnew line.
String formatting
Providesamore powerful waytoembednon-stringswithinstrings.
Stringformattingusesastring's format methodtosubstitute anumberof argumentsinthe string.
nums= [4, 5, 6]
msg = "Numbers:{0} {1} {2}".format(nums[0],nums[2],nums[3])
print(msg) -> Numbers:4 5 6
Stringformattingcan alsobe done withnamedargumets.
a = "{x},{y}".format(x=5,y=12)
print(a) -> 5, 12

String operations
Concatenation "spam"+"eggs"= spameggs
"spam"+","+"eggs"= spam,eggs
"2"+"2" = 22
1 + "2" = TypeError(ReferPythonerrorstable)
Multiplication "spam"*3 = spamspamspam
4 * "3" = 3333
"s" * "r" = TypeError
"s" * 7.0 = TypeError
Replace "hellome".replace("me","world") ->helloworld
Startswith "Thisis car".startswith("This") ->True
Endswith
Upper() "I am a boy".upper() ->I AM A BOY
Lower()
Split() "spam, eggs,ham".split(",")
Variables
In python,variablesdon'thave specifictypes,soyoucan assigna stringto a variable,andlaterassignan
integertothe same variable.
>>> a = 100
>>>print(a)
100
>>>a = "Raj"
>>>print(a)
'Raj'
Variable names:
The onlycharacters that are allowedare letter,numbersandunderscores.Also,theycan'tstart with
numbers.
NotfollowingtheserulesresultsinSyntaxErrorerror.
Pythonisa case sensitiveprogramminglanguage.Thus,Lastname andlastname are twodifferent
variable namesinPython.
Tryingto reference avariable thathasnot assignedinthe programcausesan error (NameError).
>>>a = "raj"
>>>a
raj
>>>b
NameError:name 'b' isnot defined.
>>>del a

del statement
del statementusedtoremove avariable fromprogram.
Special operators
Pythondoesn'tsupportspecial operators++and --.But,it supportsinplace operators(referoperation
table above)
Interpreterthrowssyntax errorif programuses++ or -- operators.
Example: File "./prog.py", line 12
a++
^
SyntaxError: invalid syntax
if statements
use if statementstorun code whencertainconditionholds.
if expression:
statements
Pythonusesindentation(white spacesatthe beginningof aline) todelimitblocksof code.Other
languages,suchas,C, use curlybraces to accomplishthis.But,inPythonindentationismandatory;
program won'tworkwithoutit.Asyou can see,the statementsinthe if shouldbe indented.
elif (short form of else if)
the elif (shortforelse if) statementisashortcutto use whenchainingif andelse statements.
if expression:
statement
else:
if expression:
statement
can be modifiedasbelow
if expression:
statement
elif expression:
statement

Boolean logic
Booleanlogicisusedtomake more complicatedconditionsfor itstatementsthatrelyon more than one
condition.
Python'sBooleanoperatorsare and,or, andnot.
While loops
while condition:
statement1
statement2
infinite loop
while 1==1:
print("inthe loop")
break
To enda while loopprematurely,the breakstatementcanbe used.
i = 0
while 1==1:
print(i)
i = i +1
if i >= 5:
printf("breaking")
break
continue
Unlike break, continue jumpsbackto the top of the loop,ratherthan stoppingit.
operator precedence
== has higherprecedencethan or.
Python'sorderof operationsisthe same as that of normal mathematics.
the followingtable listsall of Python'soperators,fromhighestprecedence tolowest.
Operator Description
** Exponentiation
~ + - Complement,unaryplus/minus
* / %// Multiplication,division.moduloandfloordivision
+ - Addition/subtraction
>> << Rightand leftbitwise shift
& Bitwise AND

^ | Bitwise exclusive ORandregularOR
<= < > >= Comparisons
= %= /= //= -= += *= **= Assignmentoperators
isis not Identityoperators
innot in Membershipoperator
not or and Logical operators
More on else statements
Else with loops
Usingelse withforand while loops,the code withinit iscalledif the loopfinishednormally(whena
breakstatementdoesn’tcause anexitfromthe loop)
For I inrange(10):
if (i==999):
break
Else:
print(“Unbroken”)
Else with try/except
The else statementcanalsobe usedwithtry/exceptstatements.In thiscase,the code withinitisonly
executedif noerroroccurs inthe try statement.
Try:
print(1)
exceptZeroDivisionError:
print(2)
else:
print(3)
o/P:
1
3
Lists
Listsare one type of objectin Python.Theyare usedto store an indexedlistof items.
A listiscreatedusing square brackets withcommas separatingitems.Iteminthe listcanbe accessesby
usingitsindex insquare brackets. A comma can be placedafterlastitemalso,itsvalidonly.
words= ["Hello","world","!"]
print(words[0])

print(words[1])
print(words[2])
Empty list
An emptylistiscreatedwithanemptypairof square brackets.
empty_list=[]
print(empty_list) -->o/p:[]
Nested lists
Listscan alsoinclude differentitemtypesandalsobe nestedwithinotherlists.
num= 3
things= ["string",0, [1, 2, num],4.56]
print(things[1])
print(things[2])
print(things[2][2])
Errors
IndexError:whentryto accessout of boundvalues.print(things[4])
TypeError:whentry to accessintegerorfloat typesusingindex.
No errorwill be seenforstringtype.Example,str="Helloworld",print(str[0]),o/P:H
List operations
Assignment
The itemat certainindex ina listcan be reassigned.
AdditionandMultiplication
Listscan be addedandmultipliesinthe same wayas strings
nums= [1, 2, 3]
print(nums+[4, 5, 6]) -> [1,2,3,4,5,6]
print(nums*3) -> [1,2,3,1,2,3,1,2,3]
List andstringsare similarinmanyways - stringscan be thoughtof as listsof charactersthat can't be
changed.
in operator
To check if an itemisinlist,the in operatorcan be used.It returns True if the itemoccurs one or more
timesinthe list,and False if it doesn't.

words= ["spam","eggs","spam","sause"]
print("spam"inwords) ->True
print("tomo"inwords) ->False
The in operatoris alsousedto determinewhetherornota string issubstringof anotherstring.
not operator
To check if an itemisnot ina list.
print(not4 innums) -> True
print(4not innums) -> True
Loops
words= ["hello","world","spam"]
for wordinwords:
print(word)
o/p:
hello
world
spam
for i in range(3):
print("hi")
o/p:hi hi hi
List slices
Providesmore advancedwayof retrievingvaluesfromalist.
if the firstnumberina slice isomitted,itistakentobe the start of the list.If the 2nd numberisomitted,
it istakento be the end.
squares= [0, 1, 4, 9, 16, 25]
print(squares[1:4]) ->[1, 4, 9]
print(squares[0:1]) ->[0]
print(squares[:3]) ->[0, 1, 4]
print(squares[4:]) ->[16, 25]
List slicescanalsohave a 3rd number,representingthe step,toinclude onlyalternate valuesinthe slice.
print(squares[2:5:2]) ->[4, 16]
Negativeindexing
Negative valuescanbe usedinlistslicing(andnormal listindexing).
Whennegative valuesare usedforthe firstand2nd values ina slice (ora normal index),they count
fromthe endof the list.

print(squares[1:-1]) ->[1, 4, 9, 16]
If Negative value isusedforthe step,the slice isdone backwards.Using[ : : -1] as slice isa commonand
idiomaticwaytoreverse alist.
List comprehensions
List comprehensionsare auseful wayof quicklycreatinglistswhose contentsobeyasimple rule.
cubes= [i**3 fori in range(5)]
print(cubes) ->[0, 1, 8, 27, 64]
A listcomprehensioncanalsocontainan if statementtoenforce aconditiononvaluesinthe list.
evens= [i**2 for i in range(10) if i**2 %2 == 0]
print(evens) -->[0,4, 16, 36, 64]
Tryingto create a listina veryextensive range willresultina MemoryError.
even= [2*i fori in range(10**1000)] -> MemoryError.
Thisissue issolvedby generators.
List functions
Function Description
list.append(item):isamethodof listclass and
hence can be accessedusing dot before.
Addsan itemto the endof an existinglist.
Nums= [1, 2, 3]
Nums.append(4)
Print(nums) ->[1, 2, 3, 4]
len() Get the numberof itemsina list.
print(len(nums)) ->4
list.insert(index,item) Allowstoinsertanew itemat any positioninthe
list.
Nums.insert(1, 10)
print(nums) ->[1,10, 2, 3, 4]
list.index(item) Findsthe firstoccurrence of a listitemandreturns
thisindex.
If the itemisn'tinthe list,itraisesa ValueError.
print(nums.index(10)) ->1
print(nums.index(20)) ->ValueError:20is notin
the list
max(list) Returnsthe listitemwiththe maximumvalue
min(list) Returnsthe listitemwiththe minimumvalue
list.count(item) Returnsa count of how manytimesanitemoccurs
ina list.
list.remove(item) Removesanitemfroma list
list.reverse() Reversesitemsinlist
list(range(count)):Createsa sequential listof Nums= list(range(5))

numbers.range byitself createsarange object,
and thismustbe convertedtoa list.
print(nums) ->[0,1, 2, 3, 4]
list(range(first,end)):Producesalistfromthe first
to the end
Nums= list(range(2,7))
print(nums) ->[2,3, 4, 5, 6]
list(range(first,end,interval)) Nums= list(range(2,7,2))
print(nums) ->[2,4, 6]
all and any Take a listas argumentandreturnTrue if all or any
(respectively) of theirargumentsevaluatetoTrue.
Nums= [55, 44, 33]
If all([i>5fori innums]):
print("all are largerthan5")
If any([i%2== 0 for i in nums]):
Print("atleastone iseven")
Enumerate() Usedto iterate throughthe valuesandindicesof
listsimultaneously.
For v inenumerate(nums):
Print(v)
o/p:(0, 55)
(1, 44)
(2, 33)
Sets
Setsare data structures,similartolistsordictionaries.
Theyare createdusingcurlybraces,or the set function.
num_set= {1, 2, 3, 4}
word_set= set(["spam","eggs"])
print(3innum_set) -> True
print("spam"notinword_set) -> False
To create an emptyset,youmust use set(),as{} createsan emptydictionary.
Setsare unordered,whichmeansthattheycan'tbe indexed.
Theycannot containduplicate elements.Due tothe waytheyare stored,itsfasterto check whetheran
itemispart of a set,ratherthan part of a list.
Insteadof usingappend() toadd to a set,use add()
The methodremove() removesaspecificelementfromaset, pop() removesanarbitraryelement.
Mathematical operations - union/intersection
Setscan be combinedusingmathematical operations.

unionoperator|
intersectionoperator&
difference operator-
symmetricdifference operator^
first= {1, 2, 3, 4}
sec = {4, 5, 6}
print(first|sec) -> {1, 2, 3, 4, 5, 6}
print(first&sec) -> {4}
print(first-sec) -> {1, 2, 3}
print(first^sec) -> {1, 2, 3, 5, 6}
Functions and modules
create a functionbyusingthe def statementandmustbe definedbefore theyare called,elseyouwould
see NameError.
Functionscanbe assignedandreassignedtovariablesandlaterreferencedby those values
def my_func():
print("Iamin function")
my_func()
func2 = my_func()
func2()
Arguments
Functionscanalso be usedas argumentsof otherfunctions
def my_func(word):
print(word+ "!")
my_func("Hello")
def sum(x,y):
print(x+y)
sum(5, 8)
def add(x,y):
returnx+y
def do_twice(func,x,y):
returnfunc(func(x,y),func(x,y))
a = 5
b = 10
print(do_twice(add,a,b)

Return values
def max(x,y):
if x >= y:
returnx
else:
returny
z = max(8,5)
print(z)
Docstrings
Unlike conventional comments,docstringsare retainedthroughoutthe runtime of the program.This
allowsthe programmedtoinspectthese commentsatruntime.
Modules
Modulesare piecesof code that otherpeople have writtentofulfill commontasks,suchasgenerating
randomnumbersetc.
Tryingto importa module thatisn'tavailable causesanImportError.
Usage: addimport module_name at the top of yourcode.And,access functions/variable using
module_name.var
Example:
importrandom
for i in range(5):
val = random.randint(1, 6)
print(val)
Import certainfunctions
from module_name import var
for mathimportpi
print(pi)
for mathimportpi,sqrt
print(sqrt(25))
Importa module underadifferentname using askeyword
frommath importsqrt as square_root
print(square_root(100))
Standard Library
3 typesof modules

1. those you write yourself
2. those you install fromexternal sources
3. those are pre-installedwithpython -->Standardlibrary
Tasks that can be done by usingstandardlibraryinclude
stringparsing
data serialization
testing|debugging
manipulatingdates,emails
commandline argumentsandsoon.
Python'sextensive standardlibraryisone of itsmainstrengthsasa language.
ExceptionHandling
Exceptionsoccurwhensomethinggoeswrong,due toincorrectcode orinput.
Whenan exceptionoccurs,the programimmediatelystops.
Handle exceptions:use tryand exceptstatements. Useful whendealingwithuserinput.
The try blockcontainscode that mightthrow an exception.If thatexceptionoccurs,the code inthe try
blockstopsbeingexecuted,andthe code inthe exceptblockis run.If noerror occurs, the code in the
exceptblockdoesn'trun.
try:
num1 = 7
num2 = 0
print(num1/num2)
exceptZeroDivisionError:
print("Anerroroccurreddue to zerodivision")
except(ValueError,TypeError):
print("Erroroccurred")
An exceptstatementwithoutanyexceptionspecifiedwill catchall errors.
try:
print(7/0)
except:
print("erroroccurred")
finally:
print("Thiscode will runnomatterswhat")
The finallystatementalwaysrunsaftertry/exceptblocksevenincase of exception.

Raising exception
raise statementcanbe usedto raise exceptionandspecifythe type of exceptionraised. Youcanpass
argumentfordetails.
print(1)
raise ValueError
print(2)
raise NameError("Invalidname found")
Assertions
An Assertionisasanity-checkthatyoucan turnon or turn off whenyouhave finishedtestingthe
program.
An expression istested,andif the resultcomesupfalse,andexceptionisraised.
Programmers oftenplace assertionsatthe start of a functiontocheckfor validinput,andaftera
functioncall tocheck forvalidoutput.
print(1)
assert2 + 2 == 4
print(2)
assert1 + 1 == 3
print(3)
o/p:
1
2
AssertionError
The assert can take a secondsargument thatis passedtothe AssertionErrorraisedif the assertionfails.
temp= -10
assert(temp>= 0),"Colderthanabsolute Zero!"
o/p:AssertionError:Colderthanabsolute zero!
Files handling
Opening files - open()
myfle =open("filename.txt")
The argumentof the open() functionisthe pathto the file. Youcan specifythe mode usedtoopena file
by 2nd argument.

r : Openfile inreadmode,whichisthe default.
w : Write mode,forre-writingthe contentsof the file
a : Appendmode,foraddingnewcontent tothe endof the file
b : Openfile ina binarymode,usedfornon-textfiles(image/soundfiles)
myfile =open("filename.txt","a");
myfile.close()
Reading Files - read()
cont = myfile.read()
print(cont) ->will printall the contentsof the file.
Provide numberof bytesthatreadfromfile bypassingvalue tothe read()
print(myfile.read(10)) ->10 bytesread
Afterall contentsina file have beenread,anyattempttoreadfurtherfromthat file will returnan
emptystring,because youare tryingto read from the endof the file.
To retrieve eachline inafile,use readlines function.Itreturnalistin whicheachelementisaline inthe
file.
file =open("filename.txt","r")
print(file.readline())
file.close()
o/p:
['line1n','line2n','line3']
Writing Files - write()
write() - writesastringto the file. "w"mode will create afile if notexist. If exist,the contentsof the file
will be deleted.
write() returnsthe numberof byteswrittentothe file,if successful.
file =open("new.txt","w")
file.write("Writtingtothe file")
file.close()
file =open("new.txt","r")
print(file.read())
file.close()
with statement
It ismandatoryto close the file afterread/writingthe fileevenincase of exceptionoccur.

An alternative wayof doingthisisusingwithstatement.The fileisautomaticallyclosedatthe endof
the with statement,evenif exceptionoccurwithinit.
withopen("new.txt") asf:
print(f.read())
None
representsabsence of the value.
The None objectisreturnedbyany functionthatdoesn'texplicitlyreturnanythingelse.
def myfunc():
printf("Hi")
var = myfunc()
print(var)
o/p:
Hi
None
Dictionaries
Dictionariesare datastructuresusedtomap arbitrary keystovalues. {"Key":Value}.
Emptydictionaryis{}
Each elementinadictionaryisrepresentedby key:value pair
Dictionarykeyscanbe assignedtodifferentvalueslikelists.
Tryingto index akeythat isn'tpart of the dictionaryreturnsa KeyError.
primary= {
"red":[255, 0, 0],
"green":[0,255, 0],
"blue":[0,0, 255],
}
print(primary["red"]) -->[255, 0, 0]
primary["white"] =[200, 140, 100]
primary["blue"] =[0,0, 245]
print(primary["yellow"])-->KeyError:"yellow"
Dictionarycan store any type of data as Value.
Onlyimmutable objectscanbe usedas keystodictionaries.

List anddictionariesare mutable objectsandhence can'tbe usedas keysinthe dictionary.
bad_dict= {[1,2, 3]: "one twothree",}
TypeError: unhashable type:list
Dictionary Functions
Search
Use in andnot in
nums= {1: "one",2: "two",3: "three",}
print(1in nums) -> True
print(1not in nums) -> False
print(4not in nums) -> True
get()
Usedto get the valuesbyitsindex,butif the keyisnot found,itreturnsanotherspecificvalue(2nd
argument) instead(Nonebydefault).
pairs= {1: "apple","orange":[2,3], True:False,None:"True",}
print(pairs.get("orange"))->[2,3]
print(pairs.get(7)) ->None
print(pairs.get(1234,"Notfound")) ->Notfound
Tuples
Similartolists,exceptthattheyare immutable (theycan'tbe changed).Also,these are createdusing
parenthesis,ratherthansquare brackets.
words= () -> emptytuple
words= ("spam","eggs")
or
words= "spam","eggs"
Tuple unpacking
It allowsyoutoassigneach iteminan iterable toa variable.
Numbers= (1, 2 ,3)
a, b, c = numbers
print(a) ->1
print(b) ->2

Variable*
A variable thatisprefacedwithanasterisk(*) takesall valuesfromthe iterable thatare leftoverfrom
the othervariables
A,b, *c, d = [1, 2, 3, 4 ,5 ,6, 7]
print(a) -> 1
print(b) -> 2
print(c) ->[3, 4, 5, 6]
print(d) -> 7
Ternary operator
It takesthree arguments
Status= 1
msg = “Logout” if status ==1 else “Login”
print(msg) ->Logout
Higher order functions
Lambdas
Whenfunctionsare createdusing lambdasyntax thenthe functionsare notassignedtoany variable
unlike functionscreatednormallyusing def assignsittoa variable automatically.
Stringsand integerscanbe createdonthe fly,withoutassigningthemtoavariable. Similarly,functions
can be createdwithoutassigningthemtoanyvariable usinglambdakeyword.
def my_func(f,arg):
returnf(arg)
my_func(lambdax:2*x*x, 5)
Lambda functionsgettheirname fromlambdacalculus.
Lambda functionsare notpowerful asnamedfunctions.Theycanonlydothingsthatrequire asingle
expression - usuallyequivalenttoa single line of code.
#namedfunction
def polynomial(x):
returnx**2 + 5*x + 4
print(polynomial(-4))

#lambda
print(lambdax:x**2+ 5*x + 4, -4)
Lambda functionscanbe assignedtovariables, andusedlike anormal functions
double =lambdax: x * 2
print(double(4))
map and filter
map and filteroperate onlists(orsimilarobjectscalled itterables)
Maps Lambda
def add_five(x):
returnx+5
nums= [1, 2, 3, 4, 5]
result= list(map(add_five,nums))
print(result) -> [6, 7, 8, 9, 10]
Nums= [1, 2, 3, 4, 5]
result= list(map(lambdax:x+5,nums))
print(result) -> [6,7, 8, 9, 10]
The function filterfiltersaniterable byremovingitemsthatdon'tmatch a predicate
res= list(filter(lambdax:x%2==0, nums))
print(res) -> [2, 4]
Generators
Generatorsare a type of iterable,likelistsortuples.
Unlike lists,theydon'tallowindexingwitharbitraryindices,buttheycanstill be iteratedthroughwith
for loops.
Generatorscan be createdusingfunctionsandthe yieldstatement.
def countdown():
i=5
while i>0:
yieldi
i- = 1
for i in countdown():
print(i)
o/p: 5 4 3 2 1
Yieldstatementisusedtodefine agenerator,replacingthe returnof afunctionto provide aresulttoits
calledwithoutdestroyinglocal variables.

Due to the fact thatthey yieldone itemat a time,generatorsdon'thave the memoryrestrictionsof lists.
In fact,theycan be infinite.
In short, generatorsallowsyouto declare afunction that behaveslikeaniteratori.e.itcanbe usedina
for loop.
def infinite_sevens():
while True:
yield7
for i in infinite_sevens():
print(i)
Finite generatorscanbe convertedintolistsbypassingthemasargumentstothe listfunction.Using
generatorsresultsinimprovedperformance,whichisthe resultsof the lazygenerationof values,which
translatestolowermemoryusage.Furthermore,we donotneedtowaituntil all the elementshave
beengeneratedbefore we starttouse them.
def numbers(x):
for i in range(x):
if i%2 == 0:
yieldi
print(list(numbers(11))) -> o/P:[0, 2, 4, 6, 8, 10]
Decorators
Providesawayto modifyfunctionsusingotherfunctions.
Thisis ideal whenyouneedtoextendthe functionalityof functionsthatyoudon't wantto modify.
def decor(func):
def wrap():
print("=====")
func()
print("=====")
returnwrap
def print_text():
print("Hello")
decorated= decor(print_text)
decorated()
def print_text():
print("hello")
print_text= decor(print_text)
@decor
def print_text():
print("Hello")

Object Oriented Programming
Classes
3 paradigmsof programming
1. Imperative - usingstatements,loops,andfunctionsassubroutines
2. Functional - usingpure functions,higherorderfunctions,andrecursion
3. ObjectOrientedprogramming(OOP)
Objectsare createdusingclasses,whichare actuallythe focal pointof OOP.
A Classcan be describedasan object'sblueprint,description,ordefinition.Same classcanbe usedfor
creatingmultiple differentobjects.
class Cat:
def __init__(self,color,legs):
self.color=color
self.legs=legs
def bark(self):
print("woof")
felix =Cat("ginger",4)
rover= Cat("dog-colored",4)
stumpy= Cat("brown",3)
__init__
Calledwhenaninstance (object)of the classiscreated,usingthe classname as function.
All methodsmusthave self astheirfirstparameter,althoughitisn'texplicitlypassed,pythonaddsthe
self argumenttothe listforyou; youdo not needtoinclude itwhenyoucall the methods.
The __init__ methodis calledthe classconstructor.
Methods
Definedtoaddfunctionalitytothem.
Inheritance
Inheritance providesawayto share functionalityb/w calsses.
classAnimal:
def __init__(self,name,color):
self.name =name
self.color=color
classCat(Animal):
def purr(self):
print("Purr..")

classDog(Animal):
def bark(self):
print("woof")
super().purr()
classRed_dog(Dog):
def sec_method(self):
print("secondmethod")
A classthat inheritsfromanotherclassiscalledasubclass.
A classthat is inheritedfromiscalledasuperclass.
If a classinheritsfromanotherwiththe same attributesormethods,itoverridesthem.
Super function
The function superis a useful inheritance relatedfunctionthatreferstothe parentclass.
Magic Methods
These are special methodswhicha double underscores at the beginningandendof theirnames.They
are alsoknown as dunders.
One commonuse of themis operator overloading.
Operator overloading
__add__ for + __truediv__for / __floordiv__for// __mod__ for%
__sub__ for- __and__ for & __pow__ for ** __xor__ for^ __or__ for |
classVector2D:
def __init__(self,x,y):
self.x =x
self.y=y
def __add__(self,other):
returnVector2D(self.x +other.x,self.y+other.y)
first= Vector2D(5,7)
sec = Vector2D(12, 9)
result= first+ sec
__lt__ for< __le__ for <= __eq__ for== __ne__ for!= __gt__ for > __ge__ for>=
Object Lifecycle
Made up of creation,manipulationanddestruction.

Garbage collection
The processof deletingobjectswhentheyare nolongerneedediscalled garbage collection.
Whenan object'sreference countreachesZero,pythonautomaticallydeletesit.
Data Hiding
A keypart of OOP is encapsulation, whichinvolvespackagingof relatedvariablesandfunctionsinto
single easy-to-useobject- an instance of a class.
A relatedconceptis data hiding,whichstatesthat implementationdetailsof aclassshouldbe hidden,
and a cleanstandardinterface be presentedforthose whowantto use the class.
Thiswill be done usingprivate methodsattributesinotherprogramminglanguage.
In python,there are noways of enforcingamethodor attribute be strictlyprivate.
Weeklyprivate methodsandattributeshave a single underscore atthe beginning.
Stronglyprivate methodsandattributeshave a double underscore atthe beginning.
Class methods
Classmethodsare calledbya class,whichis passedtothe cls parameterof the method.
classRectangle:
def __init__(self,width,height):
self.width=width
self.height=height
def calculate_area(self):
returnself.width*self.height
@classmethod
def new_square(cls,side_length):
returncls(side_length,side_length)
square = Rectangle.new_square(5)
print(sqaure.calculate_area())
Note:Technically,the parameters self andclsare just conventions;theycouldbe changedtoanything
else.
Static methods
These are similartoclass methods,excepttheydon'treceive anyadditional arguments;theyare
identical tonormal functionsthatbelongstoaclass.
Theyare markedwiththe staticmethod
classPizza:
def __init__(self,toppings):

self.toppings=toppings
@staticmethod
def validate_topping(topping):
if topping== "pineapple":
raise ValueError("NoPineaaple")
else:
returnTrue
ingredients=["cheese","onions","spam"]
if all(Pizza.validate_topping(i) fori iningredients):
pizza= Pizza(ingredients)
Staticmethodsbehave like plainfunctions,exceptforthe factthat youcan call themfrom an instance of
the class.
Properties
Propertiesprovide awayof customizingaccesstoinstance attributes.
Theyare createdbyputtingthe property decoratorabove a method,whichmeanswhenthe instance
attribute withthe same name as the methodisaccessed,the methodwillbe calledinstead.
One commonuse of a propertyisto make an attribute read-only.
classPizza:
def __init__(self,toppings):
self.toppings=toppings
@property
def pineapple_allowed(self):
returnFalse
@pineapple_allowed.setter
def pineapple_allowed(sefl,value):
if value:
pwd= input("Enterpassword")
if pwd== "admin"
self._pineapple_allowed=value
else
raise ValueError("Alert..Intruder")
pizza= Pizza(["cheese","tomoto"])
print(pizza.pineapple_allowed)
pizza.pineapple_allowed=True
o/p:
False
AttributeError:can'tset attribute -->If setterisnot defined

Enter password:admin
True
Propertiescanalsobe setby defining setter/getterfunctions.
The setterfunctionsetsthe correspondingpropery'svalue.
The gettergetsthe value.
Regular Expressions
RegularExpressionsare powerful tool forvariouskindsof stringmanipulation.
Matching pattern
Standardlibraryisre.
Needtoimportit andcall the belowfunction.
Importre
re.match(“spam”,“eggsspam”) ->Not found
re.search(“spam”, “eggsspam”) ->Found
re.findall(“spam”,“eggsspam”) ->[‘spam’]
Search() Findsa match of a patternanywhere inthe string
Match() Looksat the beginningof the stringonly
Findall() Returnsa listof all substringsthatmatch a pattern
Finditer() Doesthe same thingas findall() exceptitreturns
an iterator,ratherthan a list
re.search()
The search returnsan objectwithseveral methodsthatgive detailsaboutit.These methodsinclude
group() whichreturnsstringmatched, start() andend() whichreturnthe start and endingpositionsof
the match, and span() whichreturnsthe start and endpositionsasa tuple.
Importre
pattern= r”pam”
match = re.search(pattern,“eggspamsausage”)
if match:
print(match.group())
print(match.start())
print(match.end())
print(match.span())

o/p:
pam
4
7
(4, 7)
re.sub() - search & replace
sub() methodreplacesall occurrencesof the patterninstringwithreplace string,substitutingall
occurrences,unlessmax provided.
re.sub(pattern,repl,string,max=0)
importre
str = “My name is David.Hi David”
pattern= r”David”
newstr= re.sub(pattern,“Raj”,str)
print(newstr) -> My name isRaj. Hi Raj.
Metacharacters
Allowsustocreate regularexpressiontorepresentconceptslike “one ormore” repetitionsofa vowel.
. (dot)character
Thismatchesany character, otherthan a new line.
Importre
pattern= r”gr.y”
if re.match(pattern,“grey”):
print(“Match1”)
^ and $ - start and end
Thismatchesthe start and endof a string.
Patter= r”^gr.y$”
re.match(pattern,“grey”) ->True
re.match(pattern,“spamgrey”) ->False
Character classes
Provide away to matchonlyone of a specificsetof characters.
A character classis createdbyputtingthe characters itmatchesinside square brackets.
Pattern= r”[aeiou]
re.search(pattern, “grey”) - > True
re.search(pattern,“myths”) - > False

Supportsrange of charactersalso.
[a-z]-> matchesanylowercase alphabeticcharacter
[G-P]-> matchesanyuppercase characterfrom G to P
[0-9]
[A-Za-z]
^ character
Place a ^ at the start of a character class toinvert it.
Pattern= r”[^A-Z]”
re.search(“Hi Raj”) ->True
re.search(“HIRAJ”) ->False
More Metacharacters
* character
Zeroor more repetitions
+ character
One or more repetitions
? character
Zeroor one repetitions
Curlybraces
Usedto representthe numberof repetitionsb/w twonumbers.
Pattern= r”9{1, 3}$”
Re.match(pattern,“9”) ->True
re.match(pattern,“999”) -> True
re.match(pattern,“9999”) -> False
Groups
A groupcan be createdbysurroundingpartof a regularexpressionwith parenthesis.
Thismeansthat a group can be givenas an argument to metacharacterssuchas * and?
Pattern= r”egg(spam)*”
re.match(pattern,egg) ->True
re.match(pattern,spam) ->False
The contentsof groupsina matchcan be accessedusingthe group function.
A call of group(0) or group() returnsthe whole match.
A call of group(n),where nisthe greaterthan 0, returnsthe nthgroup fromthe left.

Pattern= r”a(bc)(de)(f(g)h)I”
match = re.match(pattern,“abcdefghijklmnop”)
if match:
Print(match.group())->abcdefghi
print(match.group(0)) ->abcdefghi
print(match.group(1)) ->bc
print(match.group(2)) ->de
print(match.groups()) ->(‘bc’,‘de’,‘fgh’,‘g’)
| character
Means or.
Pattern= r”gr(a|e)y”
re.match(pattern,“grey”) ->True
Named groups
Namedgroupshave format (?P<name>…),where name isthe name of the group, … isthe content.
Theybehave exactlysame asthe normal groupsexcepttheycanbe accessedby group(name) in
additiontoitsnumber.
Pattern= r”(?P<first>abc)(?:def)(ghi)”
match = re.match(pattern,“abcdefghi”)
if match:
Print(match.group(“first”)) ->abc
print(match.groups()) ->(‘abc’,‘ghi’)
Non-capturinggroups have the format (?:…).Theyare not accessible bythe groupmethods,sotheycan
be addedto an existingregularexpressionwithoutbreakingthe numbering.See above.
Special Sequences
number - Backslash
Thismatchesthe expressionof the groupof that number. 1to 99 allowed.
Pattern= r”(.+) 1”
re.match(pattern,“wordword”) ->True
re.match(pattern,“abccde”) ->False
Note:“(.+) 1” isnot the same as “(.+) (.+)”.Because, 1refersto the firstgroup’ssubexpression,which
isthe matchedexpressionitself,andnotthe regularexpressionpattern.

d and D sequence
d – matchesthe digits.
D – matchesanythingthatisn’t a digit
Pattern= r”(D+d)”
re.match(pattern,“Hi 999”) -> True
s and S sequence
s – matchesthe white spaces.
S – matchesanythingthatisn’t a white space
Pattern= r”(S+s)”
re.match(pattern,“Hi ”) -> True
w and W sequence
d – matchesthe wordcharacters.
D – matchesanythingthatisn’t a word character
A Sequence
The sequences A andZ match the beginningandendof astring,respectively.
b sequence
It matchesthe emptystringb/w wand W characters, or w characters and the beginningorendof the
string.
Informally,itrepresentsthe boundaryb/w words.
Pattern= r”b(cat)b”
re.search(pattern,“The catsat!” -> True
re.search(pattern,“we scattered”) ->False
“b(cat)b”basicallymatchesthe word“cat”surroundedbywordboundaries.
Email extraction
To extractemail like info@sololearn.com fromtext,use below pattern
Pattern= r”([w.-]+)@([w.-])(.[w.]+)”
[w.-] ->matchesone or more wordcharacter, dot or dash
Str = “Please contactinfo@sololearn.com forassistance”
match = re.search(pattern,str)
if match:

print(match.group())
o/p:info@sololearn.com
Pythonicness & Packaging
Importthis module printsthe Zenof Pythonwhenimported.
There are 20 principlesinthe Zenof Python,butonly19 linesof test.The 20th
principle isamatterof
opinion,butourinterpretationisthatthe blankline means“Use white spaces”
PEP-PythonEnhancement Proposals
PEP are suggestionsforimprovementstothe language,made byexperiencedPythondevelopers.
PEP8 is a style guide onthe subjectof writingreadablecode.
- Modulesshouldhave short,all lowercase names
- Classnamesshould be inCapWordsstyle
- Most variablesandfunctionnamesshouldbe lowercase withunderscores
- Constantsshouldbe CAPSWITH UNDERSCORES
- Namesthatwouldclashwithpythinkeywordshouldhave atrailingunderscore.
- Linesshouldn’tbe longerthan80 characters
- “from module import*”shouldbe avoided
- There shouldbe onlybe one statementperline
Packaging
Referstoputtingmodulesyouhave writteninastandardformat,so that otherprogrammerscaninstall
and use themwithease.Thisinvolvesuse of the modules setuptoolsanddisutils.
Place all the filesyouwantto putin a libraryinthe same parentdirectory.Thisdirectoryshouldalso
containa file called __init__.py,whichcan be blankbut mustbe presentinthe directory.
Thisdirectorygoesintothe otherdirectorywhichwill have readme andlicense,aswell asan important
file called setup.py
Sololearn/
License.txt
Readme.txt
Setup.py
Sololearn/
__init__.py
sololearn.py
sololearn2.py

Setup.py
Thiscontainsinformationnecessarytoassemble the package soitcan be uploadedto PyPIand istalled
withpip
From disutils.core importsetup
Setup(
name=”Sololearn”,
version=’0.1dev’,
packages=[‘sololearn’,],
license=’MIT’,
long_description=open(‘README.txt’).read(),
)
To builda source distribution
python setup.pysdist
To builda binarydistribution
python setup.pybdist
To uploadpackage
python setup.pyregister
pythin setup.pysdistupload
Install apackage with pythonsetup.pyinstall
Packaging for Users
Py2exe tool can be usedtopackage a pythonscript,alongwithlibrariesitrequires,intoasingle
executable.
PyInstallerand cx_Freeze serve the same purpose.
Function arguments
Pythonallowstohave functionwithvaryingnumberof arguments.
*args
Using*args as a functionparameterenablesyoutopassan arbitrarynumberof argumentsto that
function.The argumentsare thenaccessible asthe tuple argsinthe bodyof the function.
Def function(named_arg,*arg):
print(named_arg)
print(args)
Function(1,2,3, 4, 5)

o/p:
1
(2, 3, 4, 5)
The parameter*args must come afterthe namesparameterstoa function.The name argsis justa
convention;youcanchoose to use another.
**kwargs – keyword arguments
Thisallowsyouto handle namedargumentsthatyouhave notdefinedinadvance.
The keywordargumentsreturnsadictionary,inwhichthe keysare the argumentnames, andthe values
are the argumentvalues.
Def my_func(x,y=7,*args, **kwargs):
print(kwargs)
My_func(2,3, 4, 5, 6, a=7, b=8)
o/P:
{‘a’:7, ‘b’:8}
The argumentsreturnedbythe **kwargs are notincludedin*args.
Major 3rd party libraries
Django
The most frequentlyusedwebframeworkwritteninPython,itpowerswebsitesthatincludeInstagram
and Dicqus.
CherryPy and Flask
Are alsopopularwebframeworks
BeautifulSoup
It isveryuseful,andleadstobetterresultsforscrappingdatafromwebsites.
Matplotlib
Allowsyoutocreate a graph basedon data inpython
NumPy
It allowsforthe use of multidimentional arraysthatare much fasterthan native pythonsolutionof
nestedlists.

SciPy
Containsnumerousextensionstothe functionalityof NumPy
Panda3D
For 3D games
Pygame for2D games
List Vs Dictionary Vs Tuples Vs Sets
Lists Sets Dictionaries Tuples
List = [10, 12, 15] Set= {1, 23, 34}
Print(set) ->{1,
23,24}
Set= {1, 1}
print(set) ->{1}
Dict = {"Ram": 26, "mary":
24}
Words = ("spam",
"egss")
Or
Words = "spam",
"eggs"
Access:print(list[0]) Print(set).
Setelementscan't
be indexed.
print(dict["ram"]) Print(words[0])
List[0] = 100 Setelementscan't
be indexed.So,use
add()
Set.add(7)
Dict["Ram"] = 27 Words[0] = "care" ->
TypeError
Mutable Mutable Mutable Immutable - Values
can't be changedonce
assigned
List = [] Set= set() Dict = {} Words = ()
Fasterthan listsbut
theycan't be changed.
Slicingcanbe done
print(list[1:2]) ->[12]
Notdone. Slicingcanalsobe
done on tuples
Can't contain
duplicate elements.
Use listsif youhave a
collectionof datathat
doesn'tneedrandom
access.
Use listswhenyouneed
a simple,iterable
collectionthatis
modifiedfrequently.
- Membership
testingandthe
eliminationof
duplicate entries.
- whenyouneed
uniquenessforthe
elements.
- Whenyouneeda logical
associationb/w key:value
pair.
- whenyouneedfast
lookupforyourdata, based
on a customkey.
- whenyourdata isbeing
constantlymodified.
Use tupleswhenyour
data cannot change.
A tuple isusedin
comibnationwitha
dictionary,for
example,atuple might
representakey,
because its
immutable.

itertools -standard library
The module itertoolsisastandardlibrary.Itproducesinfiniteiterators.
count():counts upinfinitelyfromavalue
cycle():infinitelyiteratesthroughaniterable (alistora string)
repeat():repeatsanobjects,eitherinfinitelyoraspecifiednumberof times.
fromitertoolsimportcount
for i in count(3):
print(i)
if i >= 11:
break
PythonVs C
C language Pythonlanguage
Special operators(++and --) works
I.e.a++; --a;
It doesn'tsupport++ and --.Throws Syntax error.
Each statementinC endswithsemicolon; No use of ; here.
Curlybracesare usedto delimitblocksof code
If (condition)
{
Statement1;
Statement2;
}
It useswhite spacesforthispurpose
If condition:
Statement1
Statement2
Example:
If 10 > 5:
print("10 isgreaterthan 5")
if 10 > 9:
print("10isgreaterthan 9")
else:
print("5is greaterthan10")
Compilingthe programbefore executionis
mandatory
Pythonprogramdirectlyexecuted byusing
interpreter. Nocompilerhere.
Booleanoperatorsare && and || and! Booleanoperatorsare and, or and not
Uses // for one line comment
Uses /* */ for multiple line comment
Uses # for one line comment
Uses """ """ for multi line comments (Docstrings).
Uses #include toimportstandardlibraryfunctions
#include<stdio.h>
Uses importkeywordtoinclude standardlibrary
functions
Importmath
Voidassert(intexpression)
Expression -Thiscanbe a variable orany C
expression.If expressionevaluatestoTRUE,
assert() doesnothing.If expressionevaluatesto
FALSE,assert() displaysanerrormessage
on stderr(standarderrorstreamto displayerror
assertexpression
Example
assert1 + 1 == 3

messagesanddiagnostics) andabortsprogram
execution.
NULL None - representsabsence of value
Don't have automaticmemorymanagement. AutomaticGarbage collection.
Web scraping: webbrowser library
https://automatetheboringstuff.com/chapter11/
Webscrapingis the term forusinga program to downloadandprocesscontentfromthe Web.For
example,Googlerunsmanywebscrapingprogramsto index webpagesforitssearchengine.
webbrowser. Comes with Python and opens a browser to a specific page.
Webbrowser.open()
webbrowser.open(url,new=0,autoraise=True)
Displayurl usingthe defaultbrowser.If new is0,the url is openedinthe same browserwindow if
possible.If newis1,a newbrowserwindow isopenedif possible.If new is2, a new browserpage
(“tab”) is openedif possible.If autoraise isTrue,the window israisedif possible (notethatundermany
windowmanagersthiswill occurregardlessof the settingof thisvariable).
Note that onsome platforms,tryingtoopena filename usingthisfunction,mayworkandstart the
operatingsystem’sassociatedprogram.However,thisisneithersupportednorportable.
webbrowser.open_new(url)
Openurl in a newwindowof the defaultbrowser,if possible,otherwise,openurl inthe onlybrowser
window.
webbrowser.open_new_tab(url)
Openurl in a newpage (“tab”) of the defaultbrowser,if possible,otherwise equivalenttoopen_new().
webbrowser.get([name])
Returna controllerobjectforthe browsertype name.If name isempty,returna controllerfora default
browserappropriate tothe caller’senvironment.
import webbrowser
url = 'http://idiotinside.com'
# Open URL in new browser window
webbrowser.open_new(url) # opens in default browser
# Opens in safari browser
webbrowser.get('safari').open_new(url)
# Open URL in a new tab

webbrowser.open_new_tab(url) # opens in default browser
# Opens in safari browser
webbrowser.get('safari').open_new_tab(url)
Type Name Class Name Notes
'mozilla' Mozilla('mozilla')
'firefox' Mozilla('mozilla')
'netscape' Mozilla('netscape')
'galeon' Galeon('galeon')
'epiphany' Galeon('epiphany')
'skipstone' BackgroundBrowser('skipstone')
'kfmclient' Konqueror() (1)
'konqueror' Konqueror() (1)
'kfm' Konqueror() (1)
'mosaic' BackgroundBrowser('mosaic')
'opera' Opera()
'grail' Grail()
'links' GenericBrowser('links')
'elinks' Elinks('elinks')
'lynx' GenericBrowser('lynx')
'w3m' GenericBrowser('w3m')
'windows-default' WindowsDefault (2)
'macosx' MacOSX('default') (3)

Type Name Class Name Notes
'safari' MacOSX('safari') (3)
'google-chrome' Chrome('google-chrome') (4)
'chrome' Chrome('chrome') (4)
'chromium' Chromium('chromium') (4)
'chromium-browser' Chromium('chromium-browser') (4)

Introduction to Python - Running Notes

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