Writing a class inside a function in Python

Question

I am trying to write a class inside a function... something like the following:

def func(**args):
   class BindArgs(object):
       foo = args['foo']
       print 'foo is ', foo
       def __init__(self,args):
          print " hello, I am here"

f = func(foo=2)

I was hoping that print will be executed.. but the init block is not being executed... though print 'foo is ' stub runs... What am I missing?

I am trying to understand, how does this module works (https://github.com/tweepy/tweepy/blob/master/tweepy/binder.py)?

Why do you want to do this?

Martin Thoma
– Martin Thoma

2014-07-01 23:05:34 +00:00
Commented Jul 1, 2014 at 23:05 — Martin Thoma
– Martin Thoma, Commented Jul 1, 2014 at 23:05
The link is broken (404).

Peter Mortensen
– Peter Mortensen

2022-01-16 01:19:34 +00:00
Commented Jan 16, 2022 at 1:19 — Peter Mortensen
– Peter Mortensen, Commented Jan 16, 2022 at 1:19

Peter Mortensen · Accepted Answer · 2022-01-16 01:21:56Z

2

You just need to return an instance of the class...

def func(**args):
   class BindArgs(object):
       foo = args['foo']
       print 'foo is ', foo
       def __init__(self,args):
          print " hello i am here"
   return BindArgs(args) #return an instance of the class

f = func(foo=3)

If you wanted to call it later like in the example from the comments, you could just do

def func(**args):
   class BindArgs(object):
       foo = args['foo']
       print 'foo is ', foo
       def __init__(self,args):
          print " hello i am here"
   return BindArgs

f = func(foo=3)
f(args="yellow")

edited Jan 16, 2022 at 1:21

Peter Mortensen

31.4k22 gold badges110 silver badges134 bronze badges

answered Jul 1, 2014 at 23:03

Joran Beasley

114k13 gold badges167 silver badges187 bronze badges

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

5 Comments

frazman Over a year ago

So, how does this works (github.com/tweepy/tweepy/blob/master/tweepy/binder.py)

Joran Beasley Over a year ago

im guessing with the _call method that is returned at the end ... but who knows Im not sure how thats invoked or used so I couldnt tell you

Joran Beasley Over a year ago

as expected user_point=bind_api(**kwargs); user_point() they call the binding later ... since bind_api returns a method call ...

frazman Over a year ago

Where is the above line of code.. is it in api.py file

Joran Beasley Over a year ago

thats how you invoke the api_bind point that you create ... im not sure where in the code that happens... and dont want to dig but thats how you invoke it ... if you edit that file and add print statements to __init__ you will see it does not invoke until you call the returned method ... which is exactly what you would expect

Peter Mortensen · Accepted Answer · 2022-01-16 01:22:31Z

0

Inside func you're not actually initializing a new BindArgs object, so Python will not call the __init__() function. However, it does read through the class definition to use it inside the function scope, so it does execute the other print statement...

edited Jan 16, 2022 at 1:22

Peter Mortensen

31.4k22 gold badges110 silver badges134 bronze badges

answered Jul 1, 2014 at 23:04

jjwon

2041 silver badge8 bronze badges

Comments

Peter Mortensen · Accepted Answer · 2022-01-16 01:23:02Z

0

That's because init is only executed when an instance of the class is being created, which is not happening in your function. You have to explicitly call BindArgs(someobject) for that. However, the class is being defined when you call func, so the contents of the class definition are executed.

edited Jan 16, 2022 at 1:23

Peter Mortensen

31.4k22 gold badges110 silver badges134 bronze badges

answered Jul 1, 2014 at 23:05

Oliver W.

13.6k3 gold badges41 silver badges52 bronze badges

Collectives™ on Stack Overflow

Writing a class inside a function in Python

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related