[Python-Dev] Type hints -- a mediocre programmer's reaction (original) (raw)

Chris Angelico rosuav at gmail.com
Tue Apr 21 16:31:48 CEST 2015

On Tue, Apr 21, 2015 at 7:56 PM, Arnaud Delobelle <arnodel at gmail.com> wrote:

If people constantly get told by their editor / IDE that they are calling function with the wrong argument types, what are they going to do? They may start adopting the same approach as in Java / C++ etc... where interfaces must be explicitly defined and the practice of duck typing may become forgotten because discouraged by the tools programmers use.

Style guides should generally be recommending the use of concrete types for return values, but abstract types for parameters - you might well have a function that returns a list, but most functions that accept lists are really accepting sequences. Granted, there are some vague areas - how many functions take a "file-like object", and are they all the same? - but between MyPy types and the abstract base types that already exist, there are plenty of ways to formalize duck typing. And frankly, even with the uncertainties, I'd still rather have a function declared as taking a "file-like object" than "an object with a .read() method that takes an integer and returns up to that many bytes of data, and a .seek() method that blah blah blah blah". Sometimes, the precision is completely useless. What an editor would do with the hint that a function takes a file-like object I'm not sure, but if it issues a complaint because I'm passing it something that doesn't have a writelines() method, it's the fault of the editor, not the type hint.

ChrisA

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