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pythonlistmembership

Python: how to invert list membership check based on boolean variable?

How can a check for list membership be inverted based on a boolean variable?

I am looking for a way to simplify the following code:

#  variables: `is_allowed:boolean`, `action:string` and `allowed_actions:list of strings`

if is_allowed:
    if action not in allowed_actions:
        print(r'{action} must be allowed!')

else:
    if action in allowed_actions:
        print(r'{action} must NOT be allowed!')

I feel there must be a way to avoid doing the check twice, once for in and another time for not in, but can't figure out a less verbose way.

Solution

  • Compare the result of the test to is_allowed. Then use is_allowed to put together the correct error message.

    if (action in allowed_actions) != is_allowed:
    print(action, "must" if is_allowed else "must NOT", "be allowed!")