Static typing

Aahz aahz at pythoncraft.com
Sat Jul 26 00:41:15 CEST 2003


In article <mailman.1059169958.20638.python-list at python.org>,
Shane Hathaway  <shane at zope.com> wrote:
>
>Well, here's a pattern I've been trying out for this purpose: use assert 
>statements at the top of the function.
>
>def foo(bar, baz):
>     assert isinstance(bar, int)
>     assert isinstance(baz, str)
>
>I'm quite happy with the pattern, although there are a couple of 
>negative points that I can think of:
>
>- It's a bit verbose, although that verbosity enables you to perform 
>bounds checking and operate with other type systems like Zope's interfaces.
>
>- You can't specify the type of the return values this way.

You skipped the crucial negative: it breaks Python's name-based
polymorphism.  If someone creates a class that works just like a string
but doesn't derive from the str class, your program breaks for no good
reason.
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

This is Python.  We don't care much about theory, except where it intersects 
with useful practice.  --Aahz




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