[Numpy-discussion] random.uniform documentation bug?
Friedrich Romstedt
friedrichromstedt@gmail....
Tue Feb 23 14:04:43 CST 2010
Why not rewriting the definition of uniform() to:
def uniform(start, stop, low = None, high = None):
if low is not None:
start = low
if high is not None:
stop = high
[and here what matters]
This makes no trouble when a user uses either non-keyword or keyword
specification. The second pair of keywords is just for backward
compatibility. As after a keyword there is no positional argument
allowed, the only call mixing keywords and non-keywords would be
uniform(low, high = high), and this is also maintained.
Friedrich
2010/2/23 David Goldsmith <d.l.goldsmith@gmail.com>:
> On Tue, Feb 23, 2010 at 11:25 AM, Robert Kern <robert.kern@gmail.com> wrote:
>>
>> On Tue, Feb 23, 2010 at 13:05, David Goldsmith <d.l.goldsmith@gmail.com>
>> wrote:
>> > On Tue, Feb 23, 2010 at 10:29 AM, Robert Kern <robert.kern@gmail.com>
>> > wrote:
>> >>
>> >> On Tue, Feb 23, 2010 at 08:21, Alan G Isaac <aisaac@american.edu>
>> >> wrote:
>> >> > This behavior does not match the current documentation.
>> >> >
>> >> >>>> np.random.uniform(low=0.5,high=0.5)
>> >> > 0.5
>> >> >>>> np.random.uniform(low=0.5,high=0.4)
>> >> > 0.48796883601707464
>> >> >
>> >> > I assume this behavior is intentional and it is
>> >> > the documentation that is in error (for the case
>> >> > when high<=low)?
>> >>
>> >> Well, the documentation just doesn't really address high<=low. In any
>> >> case, the claim that the results are in [low, high) is wrong thanks to
>> >> floating point arithmetic. It has exactly the same issues as the
>> >> standard library's random.uniform() and should be updated to reflect
>> >> that fact:
>> >>
>> >> random.uniform(a, b)
>> >> Return a random floating point number N such that a <= N <= b for a
>> >> <= b and b <= N <= a for b < a.
>> >>
>> >> The end-point value b may or may not be included in the range
>> >> depending on floating-point rounding in the equation a + (b-a) *
>> >> random().
>> >>
>> >>
>> >> We should address the high < low case in the documentation because
>> >> we're not going to bother raising an exception when high < low.
>> >
>> > Well, an exception isn't the only option (e.g., it could return NaN),
>>
>> <shudder>
>>
>> > but
>> > does everyone agree (or at least not block) that this is acceptable
>> > behavior?
>>
>> It's a useful feature. Whenever there is a low/high pair of arguments,
>> a user frequently has to write code like so:
>>
>> low, high = min(a, b), max(a, b)
>>
>> just to satisfy the argument spec of the function. This function does
>> not really require knowing which is which for its implementation, so
>> requiring them to be one way is simply arbitrariness for the sake of
>> arbitrariness.
>
> OK.
>
>>
>> > IMO, if this function is going to allow high < low, then the doc
>> > should _also_ be _quite_ clear that if this "feature" might mess up the
>> > user's program in some way, then the user will have to implement their
>> > own
>> > safeguard against such parameters being fed to the monster. ;-)
>>
>> So do it. But please, don't use frightening terminology like you are
>> here. Just state the fact clearly and succinctly as in the
>> random.uniform() docs.
>
> Aw shucks, these docstrings are so dry. (Just kidding.) ;-)
>
> DG
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