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pythonassert
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Reputation: 401

How do you assert something is not true in Python?

In trying to understand assert in Python, specifically inverting it, I came up with this...

>>> assert != ( 5 > 2 )
>>> assert != ( 2 > 5 )

Now the first line fails and the second passes. What's the idiomatic way to assert something is false?

Upvotes: 17

Views: 28359

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1121276

You'd use the boolean not operator, not the != inequality comparison operator:

>>> assert not (5 > 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError
>>> assert not (2 > 5)

An assert passes if the test is true in the boolean sense, so you need to use the boolean not operator to invert the test.

Upvotes: 39

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