I am a beginner in python and I am trying to wrap my head around function decorators in python. And I cannot figure out how functions return functions.
I mean in what order does interpreter interprets this function:
def decorator(another_func):
def wrapper():
print('before actual function')
return another_func()
print('pos')
return wrapper
And what is the difference between these 2 statements:-
return wrapper
AND
return wrapper()
I am using Head First Python, but this topic I feel is not described very well in there, please suggest any video or a good resource so that I can understand it.
I cannot figure out how functions return functions.
As already explained by LTheriault, in python everything is an object. Not only this, but also everything happens at runtime - the def statement is an executable statement, which creates a function object from the code within the def block and bind this object to the function's name in the current namespace - IOW it's mostly syntactic sugar for some operations you could code manually (a very welcome syntactic sugar though - building a function object "by hand" is quite a lot of work).
Note that having functions as "first-class citizens" is not Python specific - that's the basis of functional programming.
I mean in what order does interpreter interprets this function:
def decorator(another_func):
def wrapper():
print('before actual function')
return another_func()
print('pos')
return wrapper
Assuming the decorator function is declared at the module top-level: the runtime first takes the code block that follows the def statement, compiles it into a code object, creates a function object (instance of type 'function') from this code object and a couple other things (the arguments list etc), and finally binds this function object to the declared name (nb: 'binds' => "assigns to").
The inner def statement is actually only executed when the outer function is called, and it's executed anew each time the outer function is called - IOW, each call to decorator returns a new function instance.
The above explanation is of course quite simplified (hence partially inexact), but it's enough to understand the basic principle.