Bug report

Bug description:

While reading the Python documentation for the random module, I noticed something that looks inconsistent between the documentation and the actual behavior of the code.

The documentation for the functions random.vonmisesvariate() and random.lognormvariate() states some restrictions for their parameters link:

• For vonmisesvariate(mu, kappa), it says that "kappa must be greater than or equal to zero".
• For lognormvariate(mu, sigma), it says that "sigma must be greater than zero".

However, the functions do not raise any error when invalid values are passed:

import random

print(random.vonmisesvariate(1, -2))   # No error
print(random.lognormvariate(1, -2))    # No error

Both functions run without any exception, even though the parameters do not meet the constraints described in the documentation.

I am wondering if this is something that should be addressed. Should the functions validate their parameters and raise an error (e.g., ValueError) for invalid inputs? Or maybe the documentation should be updated to clarify that these constraints are mathematical recommendations rather than enforced by code?

I just wanted to report this inconsistency between the documentation and the code behavior and ask for your opinion about whether this should be considered a bug or a documentation issue.

CPython versions tested on:

3.15

Operating systems tested on:

macOS

Linked PRs

• gh-135647: fix random.vonmisesvariate() and random.lognormvariate() accept invalid parameters #135717