Preferred way of determining type

Frank Mitchell frankm at bayarea.net
Fri May 18 07:30:44 CEST 2001


Alex Martelli wrote:
> 
> http://aspn.activestate.com/ASPN/Python/Cookbook/Recipe/52291
> suggests a general approach to do without type testing when you
> think you just can't do without it.  Mostly, you don't even need
> that much -- try/except most often suffices!-)
> 

Ick.  I can see the potential for a lot of redundant code to test
whether an argument is sufficiently "list-like" for a particular
purpose, using that article's method.  Yeah, maybe you don't always need
full transactionality, but (for example) testing whether you've been
handled a string or a sequence of strings is kinda annoying.

What *I* really want is a simple predicate to test whether an object is
"sequence-like", "mutable-sequence-like", "mapping-like", "string-like",
etc.  I don't care whether it's a true list, a UserList, or some random
class that implements the correct "magic methods".  Sort of like
post-hoc interface implementation.

-- 
Frank Mitchell (frankm at bayarea.net)
"The trouble with mornings is that they come when you're not awake."
-- from "A Window for Death" by Rex Stout



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