Bare Union, Callable and Tuple should not be classes #133
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This was referenced May 22, 2015
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I've been using Callable like that. What's wrong with doing so? Should I import Callable from |
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Hm, that's a good point. Pretty much anything you can do with collections.abc.X should be possible with typing.X. (This does not apply to things that aren't defined in collection.abc though, so this is not the case for Union, Tuple or List etc.) |
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gvanrossum
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Sep 27, 2016
This PR: - Fixes #136 - Fixes #133 - Partially addresses #203 (fixes the isinstance part, and multiple inheritance, still typing.Something is not a drop-in replacement for collections.abc.Something in terms of implementation). - Also fixes http://bugs.python.org/issue26075, http://bugs.python.org/issue25830, and http://bugs.python.org/issue26477 - Makes almost everything up to 10x faster. - Is aimed to be a minimalistic change. I only removed issubclass tests from test_typing and main changes to typing are __new__ and __getitem__. The idea is to make most things not classes. Now _ForwardRef(), TypeVar(), Union[], Tuple[], Callable[] are not classes (i.e. new class objects are almost never created by typing). Using isinstance() or issubclass() rises TypeError for almost everything. There are exceptions: Unsubscripted generics are still OK, e.g. issubclass({}, typing.Mapping). This is done to (a) not break existing code by addition of type information; (b) to allow using typing classes as a replacement for collections.abc in class and instance checks. Finally, there is an agreement that a generic without parameters assumes Any, and Any means fallback to dynamic typing. isinstance(lambda x: x, typing.Callable) is also OK. Although Callable is not a generic class, when unsubscribed, it could be also used as a replacement for collections.abc.Callable. The first rule for generics makes isinstance([], typing.List) possible, for consistency I also allowed isinstance((), typing.Tuple). Finally, generics should be classes, to allow subclassing, but now the outcome of __getitem__ on classes is cached. I use an extended version of functools.lru_cache that allows fallback to non-cached version for unhashable arguments.
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There is no reason for "bare" Union, Callable or Tuple (i.e. without [...]) to be a class. You shouldn't ever write
isinstance(x, Union)for example, and in their bare form these are not acceptable as annotations either.The text was updated successfully, but these errors were encountered: