[Python-bugs-list] [ python-Bugs-506647 ] random.cunifvariate() incorrect?

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Bugs item #506647, was opened at 2002-01-21 13:19
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Category: Extension Modules
Group: Python 2.1.1
Status: Open
Resolution: None
Priority: 5
Submitted By: Maciej Kalisiak (abcdefghijklmno)
Assigned to: Nobody/Anonymous (nobody)
Summary: random.cunifvariate() incorrect?

Initial Comment:
random.cunifvariate() currently is defined as:
  return (mean + arc * (self.random() - 0.5)) % _pi

First of all, this returns values in the range [0, pi)
due to the modulus, which really makes it a
semi-circular distribution, not circular (but I'm not a
mathie, so perhaps I'm wrong).

I think the normalizing step ("% _pi", or whatever this
gets changed to) should probably be mentioned in the
documentation for this function; it caught me by
surprise, and I expect it will catch some others too.  

With this defintion, the function returns a random
value in the range [mean-arc/2, mean+arc/2).  The docs
say that arc, like mean, can only be in the range
[0,pi].  This would imply that one cannot get values in
the other half of the circle, i.e. [pi, 2*pi).  Since
there doesn't seem to be anything stopping the caller
from using an arc in [0,2*pi], perhaps the
documentation should be updated?


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