Object oriented programming in python

Introduction To Python
Object Oriented Programming

Object-oriented programming
• Python is an object-oriented programming language.
• Unlike Java, Python doesn't force you to use the object-oriented paradigm
exclusively.
• Python also supports procedural programming with modules and functions,
so you can select the most suitable programming paradigm for each part of
your program.
“Generally, the object-oriented paradigm is suitable when you want to group
state (data) and behavior (code) together in handy packets of functionality.”

The class Statement
Syntax:
class classname:
statement(s)
Example:
Class baabtra :
def hello(self) :
print "Hello"
A method defined inside a class body
will always have a mandatory first
parameter, conventionally named self,
that refers to the instance on which
you call the method.

Instances
Syntax
anInstance = Class_name( )
Example
baabObject = baabtra( )

_ _init_ _
• When a class has a method named _ _init_ _, calling the class object
implicitly executes _ _init_ _ on the new instance to perform any
instance-specific initialization that is needed.
class baabtra:
def _ _init_ _(self,n):
self.x = n
baabtraInstance = baabtra(42)

Inheritance
Syntax
Derived_class(Base class_name[,Base class_name1][,Base class_name2][,...])
Example
class Baabte:
def amethod(self): print "Baaabte"
class Baabtra(Baabte):
def amethod(self): print "Baabtra“
aninstance = Baaabtra ( )
aninstance.amethod( ) # prints Baabtra

Modules
• A typical Python program is made up of several source files. Each
source file corresponds to a module, which packages program code
and data for reuse.
• Modules are normally independent of each other so that other
programs can reuse the specific modules they need.
• A module explicitly establishes dependencies upon another
module by using import or from statements.

The import Statement
Syntax
import modname [as varname][,...]
Example
import MyModule1
import MyModule as Alias

Syntax
Example
import MyModule1
In the simplest and most
common case, modname is an
identifier, the name of a variable
that Python binds to the module
object when the import
statement finishes

Syntax
Example
import MyModule1
looks for the module named
MyModule and binds the
variable named Alias in the
current scope to the module
object. varname is always a
simple identifier.

The from Statement
Syntax
from modname import attrname [as varname][,...]
from modname import *
example
• from MyModule import f

The from Statement
Syntax
from modname import attrname [as varname][,...]
from modname import *
example
• from MyModule import f Importing only one attribut
which is named as ‘f’

The Relative import
employees
employeeDetails.py
HRAccounts
My_project
userBill.py
Suppose we are here and we want to
import the file empleeDetails.py which
resides in a directory as shown

The Relative import
employees
employeeDetails.py
HRAccounts
My_project
userBill.py
import sys
import os
str_current_path = os.getcwd() ## get current working directory
str_module_path = str_current_path.replace( ' Accounts',‘HR/employees / ')
sys.path.append( str_module_path )
import employeeDetails

The Relative import
sys.path
– A list of strings that specifies the search path for modules
sys.path.append( module path )
– This statement append our module path with the existing list of
sys.path, then the import statement search for the module in the
module path as we specified.

_ _ main _ _
• When the Python interpreter reads a source file, it executes all of the code found
in it. But Before executing the code, it will define a few special variables.
• For example, if the python interpreter is running a module (the source file) as
the main program, it sets the special __name__ variable to have a
value"__main__".
• If this file is being imported from another module, __name__ will be set to the
module's name.

def func():
print("func() in one.py")
print("top-level in one.py")
if __name__ == "__main__":
print("one.py is being run directly")
else:
print("one.py is being imported into another
module")
import one
print("top-level in two.py")
one.func()
if __name__ == "__main__":
print("two.py is being run directly")
else:
print("two.py is being imported into
another module")
# file two.py# file one.py
Example

def func():
if __name__ == "__main__":
else:
module")
import one
one.func()
if __name__ == "__main__":
else:
another module")
Example
When we run one.py
-----------------------------
Top-level in one.py
One.py is being run directly

def func():
if __name__ == "__main__":
else:
module")
import one
one.func()
if __name__ == "__main__":
else:
another module")
Example
When we run two.py
-----------------------------
Top-level in one.py
one.py is being imported into another module
Top-level in two.py
Func() in one.py
two.py is being run directly

Questions?
“A good question deserve a good grade…”

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Object oriented programming in python

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