Overhead of creating classes in Python: Exact same code using class twice as slow as native DS?

Question

I created a Stack class as an exercise in Python, using all list functions. For example, Stack.push() is just list.append(), Stack.pop() is list.pop() and Stack.isEmpty() is jus

Answer 1

There is an inherent overhead using functions (where methods on an instance are just wrappers around functions to pass in self).

A function call requires the current function information (a frame) to be stored on a stack (the Python call stack), and a new frame to be created for the function being called. That all takes time and memory:

>>> from timeit import timeit
>>> def f(): pass
...
>>> timeit(f, number=10**7)
0.8021022859902587

There is also a (smaller) cost of looking up the attribute (methods are attributes too), and creating the method object (each attribute lookup for a method name causes a new method object to be created):

>>> class Foo:
...     bar = None
...     def baz(self): pass
...
>>> timeit('instance.bar', 'from __main__ import Foo; instance = Foo()', number=10**7)
0.238075322995428
>>> timeit('instance.baz', 'from __main__ import Foo; instance = Foo()', number=10**7)
0.3402297169959638

So the sum cost of attribute lookup, method object creation and call stack operations add up to the extra time requirements you observed.