[Python-ideas] Pre-PEP: adding a statistics module to Python

[Steven D'Aprano]

On 04/08/13 11:51, Steven D'Aprano wrote:

> I don't know enough C to volunteer to do that. If the built-in sum() is improved to the point it passes my unit tests, I would consider using it in the future.

Actually, on further thought, I don't think I would. A statistic sum should be restricted to only operate on numbers, not on arbitrary non-numeric values that happen to support the + operator (e.g. lists). As far as I know, the *only* stats function that is defined to work with non-numeric data is mode() (which my code supports). So even if the built-in was improved, I'd still need to wrap it with something vaguely like this:

def sum(data, start=0):
     if not isinstance(start, numbers.Number):
         raise ...
     result = builtins.sum(data, sum)
     if not isinstance(result, numbers.Number):
         raise ...
     return result


(In hindsight, the decision to allow built-in sum to support non-numbers seems more and more unfortunate to me.)

Being able to add numbers, and get a nice error if a non-numeric type slips into your data, is part of the API for statistics libraries. Built-in sum() doesn't meet that requirement. That they happen to have the same name is neither here nor there. That's why we don't force everything into one giant flat namespace.



-- 
Steven