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mitar opened this issue Aug 14, 2017 · 2 comments
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Cannot copy class inheriting from generic #458

mitar opened this issue Aug 14, 2017 · 2 comments

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@mitar
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mitar commented Aug 14, 2017

Example:

Python 3.6.2 (default, Jul 17 2017, 16:44:32) 
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import typing
>>> class Foo(typing.Sequence):
...   pass
... 
>>> Foo.__copy__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 1189, in __copy__
    self.__extra__, self.__orig_bases__)
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 953, in __new__
    assert origin is not None
AssertionError
>>> typing.Sequence.__copy__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 1189, in __copy__
    self.__extra__, self.__orig_bases__)
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 953, in __new__
    assert origin is not None
AssertionError
>>> typing.Sequence[typing.T_co].__copy__()
typing.Sequence[+T_co]
@mitar
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mitar commented Aug 14, 2017

As you see, also unbound generic cannot be copied.

@ilevkivskyi
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You should never call __copy__ directly, it only exists for backwards compatibility with Python 3.2 (which was removed recently due to Python 3.2 reaching EoL, so that __copy__ could be actually removed at any time).

@izquierdo izquierdo mentioned this issue Nov 4, 2017
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@mitar @ilevkivskyi