Environment variable to boolean in Python ( False in [0,"0"] == True )

Question

I want to decide project's status (production/development) by checking if there is a PRODUCTION environment variable.

The problem is that, surprisingly, this code returns True when there is no PRODUCTION environment variable:

PRODUCTION = True if os.getenv('PRODUCTION', False) in [0,"0"] else False # !!! In Bash, 0 means true and 1 false

The thing is that False in [0,"0"] gives True which I didn't know until now. I know that if 0 is the same as if False but this surprised me.

How to make it work and why it behaves like that?

EDIT

Solved this way but I'm still curious why the "in" statement works like that.

PRODUCTION = True if str(os.getenv('PRODUCTION', 1)) == "0" else False # !!! In Bash, 0 means true and 1 false

I think `in` is basically doing `==` comparisons (note that `False == 0` evaluates `True`) - you can get a similar thing if comparing between integers and (integer-valued) floats. — alani, Jun 16 '21 at 18:06
Can you please clarify what confuses you about the in operator? You seem to already know that False is equal to 0. So `False in [0,...]` because there is an element equal to False in the list. — MisterMiyagi, Jun 16 '21 at 18:08
Asked differently, what do you think the in operator is doing, and why do you think this means you "should" get a different result? — MisterMiyagi, Jun 16 '21 at 18:12

ti7 · Answer 1 · 2021-06-16T18:20:21.223

0

As you're reading from the environmental dict with .get(), you could instead index it and let it raise KeyError

try:
    prod = bool(os.environ["PRODUCTION"] == PROD_FLAG)
except KeyError:  # PRODUCTION not in env dict
    prod = False

If you're really interested in forms of "false", stringify 'em

if "false" in [str(x).lower() for x in iterable]

The problem with your initial solution is that 0 is equal to False in Python, which is not immediately obvious

>>> False == 0
True
>>> False in [0]
True
>>> False is 0
<stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="?
False

edited Jun 16 '21 at 18:20

answered Jun 16 '21 at 18:04

ti7

This is *not* about falsy'ness. The empty list is falsy, but it is not in `[0, "0"]` and False is not in `[[], "0"]`. – MisterMiyagi Jun 16 '21 at 18:16
@MisterMiyagi their `.getenv()` solution compares each value in `[0, "0"]` to `False`, and they're surprised the first is non-obviously `True` – ti7 Jun 16 '21 at 18:17
Yes, and this is *not* due to falsy'ness. Most other falsy values will behave differently than 0 here. – MisterMiyagi Jun 16 '21 at 18:18
1

Oh, I see what you mean, indeed it's _equal_ to False (though not literally `is False` ..), rather than Falsey – ti7 Jun 16 '21 at 18:18

1 Answers1