Object oriented programming in python

1. Introduction To Python
Object Oriented Programming

2. 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.”

3. 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.

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

5. _ _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)

6. 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

7. 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.

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

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

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

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

12. 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’

13. 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

14. 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

15. 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.

16. _ _ 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.

17. 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

18. 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
When we run one.py
-----------------------------
Top-level in one.py
One.py is being run directly

19. 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
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

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

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