Function inside function - every time?

Question

Let we have this code:

def big_function():     def little_function():          .......     ......... 

The Python documentation says about def statement:

A function definition is an executable statement. Its execution binds the function name...

So, the question is: Does def little_function() execute every time when big_function is invoked? Question is about def statement exactly, not the little_function() body.

Answer 1

You can check the bytecode with the dis module:

>>> import dis >>> def my_function(): ...     def little_function(): ...             print "Hello, World!" ...      ...  >>> dis.dis(my_function)   2           0 LOAD_CONST               1 (<code object little_function at 0xb74ef9f8, file "<stdin>", line 2>)               3 MAKE_FUNCTION            0               6 STORE_FAST               0 (little_function)               9 LOAD_CONST               0 (None)              12 RETURN_VALUE   

As you can see the code for the inner function is compiled only once. Every time you call my_function it is loaded and a new function object is created(in this sense the def little_function is executed every time my_function is called), but this doesn't add much overhead.