A mean docstring?

Fernando Perez fperez.net at gmail.com
Tue Oct 10 14:33:36 CDT 2006

Hi all,

I was updating some old Numeric code to be more 'numpythonic' (it
works, but uses a lot of Numeric-style cruft), and read the a.mean()
docstring that says:

    If axis is None, this equals:
        a.sum(axis, dtype) * 1.0 / product(a.shape,axis=0)

Is this convoluted form of the denominator really needed?  Isn't it
equivalent to a.size?  A few quick tests (and my understanding of
numpy's new attributes) seem to indicate so:

In [78]: a=rand(1,2,3,4); product(a.shape,axis=0)==a.size
Out[78]: True

In [79]: a=rand(2,3,4,2); product(a.shape,axis=0)==a.size
Out[79]: True

In [80]: a=rand(2); product(a.shape,axis=0)==a.size
Out[80]: True

In [81]: a=rand(2,4,4); product(a.shape,axis=0)==a.size
Out[81]: True

So my question is two-fold (assuming the above is correct in all cases):

1. Should the docstring be changed to simply say

    If axis is None, this equals:
        a.sum(axis, dtype) * 1.0 / a.size

This is clearer to readers, and promotes the use of .size as a quick
and correct way of getting an array's size.

2. Does the implementation actually used the more complicated
product() approach, or does it just read .size?  I'm wondering about



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