[Python-ideas] Consider adding clip or clamp function to math

[Neil Girdhar]

It's common to want to clip (or clamp) a number to a range.  This feature 
is commonly needed for both floating point numbers and integers:

http://stackoverflow.com/questions/9775731/clamping-floating-numbers-in-python
http://stackoverflow.com/questions/4092528/how-to-clamp-an-integer-to-some-range-in-python

There are a few approaches: 

* use a couple ternary operators 
(e.g. https://github.com/scipy/scipy/pull/5944/files  line 98, which 
generated a lot of discussion)
* use a min/max construction,
* call sorted on a list of the three numbers and pick out the first, or
* use numpy.clip. 

Am I right that there is no *obvious* way to do this?  If so, I suggest 
adding math.clip (or math.clamp) to the standard library that has the 
meaning:

def clip(number, lower, upper):
    return lower if number < lower else upper if number > upper else number

This would work for non-numeric types so long as the non-numeric types 
support comparison.  It might also be worth adding

assert lower < upper

to catch some bugs.

Best,

Neil
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