Understanding the Init in Python

Question

Consider i create a Class Name "Application" which accepts "frame" widget

class Application(Frame):

In Constructor/Initialisation i do

def __init__(self, master=None):

When creating Instance

root = Tk()
app = Application(master=root)

i dont Understand when creating instance i am assigning instance of class Tk() to Master . then why in initialisation we are making it "None". can Some one look into this and Explain.

Thanks in Advance

BrenBarn · Accepted Answer · 2013-11-09 08:46:46Z

5

When you write def __init__(self, master=None): you are setting None as the default value of master. When you call Application(master=root) you are passing a value that overrides the default.

A simple example:

def foo(a=1):
    print "a is", a

>>> foo()
a is 1
>>> foo(2)
a is 2
>>> foo(a=2)
a is 2
>>>

edited Nov 9, 2013 at 8:46

answered Nov 9, 2013 at 8:18

BrenBarn

253k39 gold badges421 silver badges392 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Prag Rao Over a year ago

Hi !! thnks for explanation. is there any rule/documentation which explains this in more detail. i got the point but technically still i am not able to understand. when i make a call to foo(with no arguments) its fine a gets default value. but when i pass some argument still it should get default value. why the default value is ignored ??

BrenBarn Over a year ago

@PragRao: When you pass a value, it overrides the default value. That's what "default" means: it means its the value that is used if you don't specify any other value. You can start with the Python tutorial for more info.

Collectives™ on Stack Overflow

Understanding the Init in Python

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related