Cannot append to a returned list?

Question

def f():
    lst = [\'a\', \'b\', \'c\']
    return lst[1:]

why is f().append(\'a\') is None == True even though f().__class__

Answer 1

In this context it's always good to be fully aware of the difference between expressions and commands. There are basically two ways to append a value x to a list l

1. Using a command: l.append(x). Usually a command doesn't return any value; it performs some kind of side-effect.
2. Using an expression, namely l+[x] which stands for a value and does nothing. I.e. you assign l=l+[x]

Answer 2

Because append() modifies the list, but does not return it.

Answer 3

Try this:

f()+['a']

Hope this helps

Answer 4

Because append() returns None and not the list object. Use

l = f()
l.append('a')
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