[Python-Dev] PEP 450 adding statistics module

[Oscar Benjamin]

On 8 September 2013 18:32, Guido van Rossum <guido at python.org> wrote:
> Going over the open issues:
>
> - Parallel arrays or arrays of tuples? I think the API should require
> an array of tuples. It is trivial to zip up parallel arrays to the
> required format, while if you have an array of tuples, extracting the
> parallel arrays is slightly more cumbersome. Also for manipulating of
> the raw data, an array of tuples makes it easier to do insertions or
> removals without worrying about losing the correspondence between the
> arrays.

For something like this, where there are multiple obvious formats for
the input data, I think it's reasonable to just request whatever is
convenient for the implementation. Otherwise you're asking at least
some of your users to convert data from one format to another just so
that you can convert it back again. In any real problem you'll likely
have more than two variables, so you'll be writing some code to
prepare the data for the function anyway.

The most obvious alternative that isn't explicitly mentioned in the
PEP is to accept either:

def correlation(x, y=None):
    if y is None:
        xs = []
        ys = []
        for x, y in x:
            xs.append(x)
            ys.append(y)
    else:
        xs = list(x)
        ys = list(y)
        assert len(xs) == len(ys)
    # In reality a helper function does the above.
    # Now compute stuff

This avoids any unnecessary conversions and is as convenient as
possible for all users at the expense of having a slightly more
complicated API.


Oscar