Lessons · Python · what counts as true

What counts as true

Empty things are false. Anything with something in it is true.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

It is why 'if items:' reads so cleanly instead of 'if len(items) > 0:'. Once you know the rule, a lot of real code stops looking like magic.

How to think about it

Ask: am I checking whether this EXISTS, or whether it has CONTENT? They are different questions, and None is not the same as empty.

Worked example

items = []

An empty list.

if items:

Empty counts as false, so this block does not run.

    print("has things")

Skipped.

print(bool("0"))

True. Any text with characters in it is true, including the character zero.

Your turn

Print "nothing here" when a list is empty.

items = []
if  items:
    print("nothing here")

The trap

0 is false and "0" is true. So is "False". The rule is about emptiness, not about what the characters spell.

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