[].append(x) behaviour

Question

This executes as I\'d expect:

>>>x=[]
>>>x.append(3)
>>>x
[3]

Why does the following return None?

&g         


        

Answer 1

because list.append changes the list itself and returns None ;)

You can use help to see the docstring of a function or method:

In [11]: help(list.append)
Help on method_descriptor:

append(...)
    L.append(object) -- append object to end

EDIT:

This is explained in docs of python3:

Some collection classes are mutable. The methods that add, subtract, or rearrange their members in place, and don’t return a specific item, never return the collection instance itself but None.