Python programming workshop

Python Programming
Workshop
Pramote Kuacharoen

Topics
 Expressions, operators, precedence, control flows, functions
 Input/output
 List
 Classes and Objects
2

The Python Interpreter
 Python is an interpreted language
 Commands are executed through the Python interpreter
 A programmer defines a series of commands in advance and saves those
commands in a text file known as source code or a script.
 For Python, source code is conventionally stored in a file named with the .py
suffix (e.g., demo.py)
3

Writing a Simple Program
 Algorithm for calculating the area of a square
 Obtain the width from the user
 Computer the area by applying the following formula
 𝒂𝒓𝒆𝒂 = 𝒘𝒊𝒅𝒕𝒉 ∗ 𝒘𝒊𝒅𝒕𝒉
 Display the result
4

Reading Input from the Console
 Use the input function to obtain a string
 variable = input(‘Enter width : ’)
 Use the eval function to evaluate expression
 variable = eval(string_variable)
 Combination
 width = eval(input(‘Enter width : ’))
5

Calculating Square Area
width = eval(input('Enter width : '))
area = width * width
print('Area is ', area)
6

Identifiers
 Identifiers in Python are case-sensitive, so temperature and Temperature are
distinct names.
 Identifiers can be composed of almost any combination of letters, numerals,
and underscore characters.
 An identifier cannot begin with a numeral and that there are 33 specially
reserved words that cannot be used as identifiers:
7

Types
 Python is a dynamically typed language, as there is no advance declaration
associating an identifier with a particular data type.
 An identifier can be associated with any type of object, and it can later be
reassigned to another object of the same (or different) type.
 Although an identifier has no declared type, the object to which it refers has
a definite type. In our first example, the characters 98.6 are recognized as a
floating-point literal, and thus the identifier temperature is associated with
an instance of the float class having that value.
8

Numerical Data Types ad Numeric
Operators
 integer: e.g., 3, 4
 float: e.g., 3.0, 4.0
Name Meaning Example Result
+ Addition 34 + 1 35
- Subtraction 34.0 – 0.1 33.9
* Multiplication 300 * 30 9000
/ Float Division 1 / 2 0.5
// Integer Division 1 // 2 0
** Exponentiation 4 ** 0.5 2.0
% Remainder 20 % 3 2
9

Boolean Data Types
 Often in a program you need to compare two values, such as whether i is
greater than j
 There are six comparison operators (also known as relational operators) that
can be used to compare two values
 The result of the comparison is a Boolean value: true or false
Operator Name
< less than
<= less than or equal to
> greater than
>= greater than or equal to
== equal to
!= not equal to
10

String
 Sequence of characters that is treated as a single item
 Written as a sequence of characters surrounded by either single quotes (') or
double quotes (")
 Position or index of a character in a string
 Identified with one of the numbers 0, 1, 2, 3, . . . .
11

List
12
list1 = list() # Create an empty list
list2 = list([2, 3, 4]) # Create a list with elements 2, 3, 4
list3 = list(["red", "green", "blue"]) # Create a list with strings
list4 = list(range(3, 6)) # Create a list with elements 3, 4, 5
list5 = list("abcd") # Create a list with characters a, b, c
list1 = [] # Same as list()
list2 = [2, 3, 4] # Same as list([2, 3, 4])
list3 = ["red", "green"] # Same as list(["red", "green"])
append(x: object): None
insert(index: int, x: object): None
remove(x: object): None
index(x: object): int
count(x: object): int
sort(): None
reverse(): None
extend(l: list): None
pop([i]): object

List Is a Sequence Type
13
Operation Description
x in s True if element x is in sequence s
x not in s True if element x is not in sequence s
s1 + s2 Concatenates two sequences s1 and s2
s * n, n * s n copies of sequence s concatenated
s[i] ith element in sequence s
s[i : j] Slice of sequence s from index i to j - 1
len(s) Length of sequence s, i.e., the number of elements in s
min(s) Smallest element in sequence s
max(s) Largest element in sequence s
sum(s) Sum of all numbers in sequence s
for loop Traverses elements from left to right in a for loop
<, <=, >, >=, ==, != Compares two sequences

if Statement
14
if width > 0:
if Boolean-expression:
statement(s)

if-else Statement
15
if width > 0:
else:
print(‘width must be positive’)
if Boolean-expression:
statement(s) for the true case
else:
statement(s) for the false case

Multiple Alternative for if Statements
16
if score >= 90.0:
grade = 'A'
elif score >= 80.0:
grade = 'B'
elif score >= 70.0:
grade = 'C'
elif score >= 60.0:
grade = 'D'
else:
grade = 'F'
if score >= 90.0:
grade = 'A'
else:
if score >= 80.0:
grade = 'B'
else:
if score >= 70.0:
grade = 'C'
else:
if score >= 60.0:
grade = 'D'
else:
grade = 'F'

Logical Operators
17
Operator Description
not Logical negation
and Logical conjunction
or Logical disjunction
(year % 4 == 0 and year % 100 != 0) or year % 400 == 0)
A year is a leap year if it is divisible by 4 but not by 100, or it is divisible by 400.

Conditional Operator
18
y = 1 if x > 0 else -1if x > 0:
y = 1
else:
y = -1
if num % 2 == 0:
print(str(num) + “is even”)
else:
print(str(num) + “is odd”);
print("number is even" if (number % 2 == 0)
else "number is odd")

Operator Precedence
 +, - unary
 **
 not
 *, /, //, %
 +, -
 <, <=, >, >=
 ==, !=
 and
 or
 =, +=, -=, *=, /=, //=, %= (Assignment operator)
19

Loops
20
for i in range(1, 6):
print (i)
num = 1
while num <= 5:
print(num)
num += 1
while conditions:
indented block of statements
for var in sequence:
indented block of statements

Functions
 Functions can be used to define reusable code and organize and simplify code
21
def sum_range(a, b):
result = 0
for i in range(a, b+1):
result += i
return result
def main():
print('Sum from 1 to 10 is ', sum_range(1, 10));
print('Sum from 50 to 100 is ', sum_range(50, 100));
main()
def function_name(list of parameters):
# Function body

Reading Input from Text Files
22
continent = input('Enter the name of a continent : ')
continent = continent.title()
if continent != 'Antarctica':
infile = open('UN.txt', 'r')
for line in infile:
data = line.split(',')
if data[1] == continent:
print(data[0])
else:
print('There are not countries in Antarctica.')
infile = open(‘Filename’, ‘r’)

List Comprehension
23
list1 = [x for x in range(5)]
[0, 1, 2, 3, 4]
line = input('Enter series of numbers : ')
text_numbers = line.split(' ')
numbers = [eval(num) for num in text_numbers]

Objects and Classes
 Object-oriented programming enables you to develop large-scale software
and GUIs effectively.
24
class Rectangle:
def __init__(self, width = 1, height = 2):
self._width = width
self._height = height
def area(self):
return self._width * self._height
def perimeter(self):
return 2 * (self._width * self._height)
def main():
r1 = Rectangle(10, 20)
print('The area of the rectangle is : ', r1.area())
print('The perimeter of the rectangle is : ', r1.perimeter())
main()
class ClassName:
initializer
methods

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