Empty list and boolean value

Question

I understand that I can test if a list is empty like this:

l = []
if not l:
    print("empty")

But I do not understand why the next code isn't equivalent:

if l == False:
    print("empty")

@julivicoit's not simple if you are new to Python. The key point is that `if not l` is actually implicitly invoking the bool() conversion on `l`. — Steve, Jul 15 '16 at 09:53
@SteveHaigh: U are right. Now i can't edit my comment any more. So sorry for this! — qvpham, Jul 15 '16 at 09:56

score 0 · Accepted Answer · answered Jul 15 '16 at 09:44

0

l itself is list type so comparing it with boolean will always return False

not l is boolean expression so it will return True sometimes depending on if l is empty or not

    >>>l = []
    >>>type(l)
    <type 'list'>
    >>>l == True
    False
    >>>l == False
    False
    >>>
    >>>
    >>> type(not l)
    <type 'bool'>
    >>> (not l) == False
    False
    >>> (not l) == True
    True

answered Jul 15 '16 at 09:44

m.antkowicz

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So why `0` is different from `[]`? It type is `int` but not `bool` – Ohad Eytan Jul 15 '16 at 09:49
why different? `not 0` is also `True` – m.antkowicz Jul 15 '16 at 09:50
`0 == False` return `True` – Ohad Eytan Jul 15 '16 at 09:50
I saw the answer in the linked post. That's because bool is subclass of int – Ohad Eytan Jul 15 '16 at 09:55

Empty list and boolean value

1 Answers1