[Python-Dev] Remove typing from the stdlib (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Sun Nov 5 21🔞24 EST 2017

On 4 November 2017 at 02:46, Eric V. Smith <eric at trueblade.com> wrote:

On 11/3/2017 12:15 PM, Victor Stinner wrote:

Hi, 2017-11-03 15:36 GMT+01:00 Guido van Rossum <guido at python.org>:

Maybe we should remove typing from the stdlib? https://github.com/python/typing/issues/495 The typing module is not used yet in the stdlib, so there is no technically reason to keep typing part of the stdlib. IMHO it's perfectly fine to keep typing and annotations out of the stdlib, since the venv & pip tooling is now rock solid ;-) I'm planning on using it for PEP 557: https://www.python.org/dev/peps/pep-0557/#class-variables The way the code currently checks for this should still work if typing is not in the stdlib, although of course it's assuming that the name "typing" really is the "official" typing library. # If typing has not been imported, then it's impossible for # any annotation to be a ClassVar. So, only look for ClassVar # if typing has been imported. typing = sys.modules.get('typing') if typing is not None: # This test uses a typing internal class, but it's the best # way to test if this is a ClassVar. if type(atype) is typing.ClassVar: # This field is a ClassVar. Ignore it. continue See also https://github.com/ericvsmith/dataclasses/issues/14

That particular dependency could also be avoided by defining an "is_class_var(annotation)" generic function and a "ClassVar" helper object in the dataclasses module. For example:

class _ClassVar:
    def __init__(self, annotation):
        self.annotation = annotation

class _MakeClassVar:
    def __getitem__(self, key):
        return _ClassVar(key)

ClassVar = _MakeClassVar()

@functools.singledispatch
def is_class_var(annotation):
    return isinstance(annotation, _ClassVar)

It would put the burden on static analysers and the typing module to understand that dataclasses.ClassVar meant the same thing conceptually as typing.ClassVar, but I think that's OK.

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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