Dictionary Truth Value Testing

Question

>>> dict = {}
>>> a=2
>>> if a is not None and dict is None:
...     print("lol")
... else:
...     print(" Print result is a")
... 
   result is a

Why does the first if statement does not run? I am specifying that thedictis empty and that" a"` exists.

Reference: https://docs.python.org/2/library/stdtypes.html#truth-value-testing

`{}` is not `None`, `None` is `None`. – zwer Jul 24 '18 at 01:05 — zwer, Jul 24 '18 at 01:05

score 1 · Answer 1 · answered Jul 24 '18 at 01:06

1

I am specifying that the dict is empty and that "a" exists.

No, you're not. You're testing whether a is not identical to None (true) and if {} is identical to None (false).

What you want is a and not d. You almost never want to compare with a boolean, and you certainly never want to do it with is.

answered Jul 24 '18 at 01:06

Ignacio Vazquez-Abrams

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Thank you, That cleared up a lot of confusion! :) – Yazzz Jul 24 '18 at 01:09

Carcigenicate · Answer 2 · 2018-07-24T01:25:02.593

1

Because the dictionary isn't None.

There's a difference between a value being falsey, and it satisfying is None.

Just test the truthiness directly:

if a is not None and not dict:

As noted in the comments though, don't name variables the same as existing function names. That's just asking for 'dict' object is not callable errors in the future.

edited Jul 24 '18 at 01:25

answered Jul 24 '18 at 01:08

Carcigenicate

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Wouldn't use `dict` as var name – rafaelc Jul 24 '18 at 01:17
@RafaelC I'm using the same name as the OP for clarity. I'll add a note. – Carcigenicate Jul 24 '18 at 01:18

Dictionary Truth Value Testing

2 Answers2