Invalid base class on Protocol (typing_extensions) #296

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1. rchen152 commented on Apr 16, 2019

   

   rchen152

   on Apr 16, 2019

   Contributor

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   Thanks for the report! I think there are two things going on here:

   • pytype defines Protocol in typing rather than typing_extensions. Fixing this should be easy enough.
   • We don't yet support defining and using a protocol in the same module. I'll take a look and figure out what we'd need to do to support this.
2. rchen152

   self-assigned this

   on Apr 16, 2019
3. rchen152

   added

   bug

   on Apr 16, 2019
4. autumnjolitz commented on Apr 16, 2019

   

   autumnjolitz

   on Apr 16, 2019

   Author

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   I isolated my Protocol subclasses out to a project specific typing.py file. While calling python -m pytype.tools.analyze_project.main on files that from .typing import ... worked, calling it directly on this typing.py file would throw errors (zero uses of the defined classes).

   This is quite surprising, because it almost works (project level analysis faults, but calling pytype on modules that use the Protocol definitions will work as long as you keep pytype away from the actual files that define the Protocols)

   Example:

   (python) Fateweaver:~/software$ mkdir module
   (python) Fateweaver:~/software$ echo '' > module/__init__.py
   (python) Fateweaver:~/software$ cat > module/typing.py
   import typing
   if typing.TYPE_CHECKING:
       from typing import Protocol
   else:
       try:
           from typing import Protocol
       except ImportError:
           from typing_extensions import Protocol
   
   
   class IReadlineable(Protocol):
       def readline(self) -> bytes:
           ...
   
   (python) Fateweaver:~/software$ cat > module/test.py
   from typing import List
   from .typing import IReadlineable
   
   
   def foo(fh: IReadlineable) -> List[bytes]:
       items = []
       for line in iter(fh.readline, b''):
           items.append(line)
       return items
   
   
   if __name__ == '__main__':
       import io
       test_buffer = io.BytesIO(b'foo\nbar')
       assert foo(test_buffer) == [b'foo\n', b'bar']
   
   (python) Fateweaver:~/software$ python -m module.test
   (python) Fateweaver:~/software$ mypy module
   (python) Fateweaver:~/software$ python -m pytype.tools.analyze_project.main module/test.py
   Computing dependencies
   Analyzing 1 sources with 1 local dependencies
   ninja: Entering directory `/Users/ben/software/.pytype'
   [2/2] check module.test
   Success: no errors found
   (python) Fateweaver:~/software$ python -m pytype.tools.analyze_project.main module
   Computing dependencies
   Analyzing 3 sources with 0 local dependencies
   ninja: Entering directory `/Users/ben/software/.pytype'
   [2/3] check module.typing
   FAILED: /Users/ben/software/.pytype/pyi/module/typing.pyi
   pytype-single --imports_info /Users/ben/software/.pytype/imports/module.typing.imports --module-name module.typing -V 3.7 -o /Users/ben/software/.pytype/pyi/module/typing.pyi --analyze-annotated --nofail --quick /Users/ben/software/module/typing.py
   File "/Users/ben/software/module/typing.py", line 13, in readline: bad option in return type [bad-return-type]
     Expected: bytes
     Actually returned: None
   
   For more details, see https://google.github.io/pytype/errors.html#bad-return-type.
   ninja: build stopped: subcommand failed.
   (python) Fateweaver:~/software$
   
5. rchen152 commented on Apr 17, 2019

   

   rchen152

   on Apr 17, 2019

   Contributor

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   The bad-return-type error is because pytype is trying to check the empty method body against the declared return type :(

   I've mailed out fixes for all of these issues; they'll be exported to GitHub sometime today and should be in this Friday's release assuming nothing breaks.
6. rchen152

   added 4 commits that reference this issue on Apr 17, 2019

   Support importing Protocol from typing_extensions.

   ...

   a9cf786

   Support custom protocols in pyi files.

   ...

   2b3f738

   Support using a protocol in the same module that defines it.

   ...

   25b6a06

   Be more careful about type-checking protocol method bodies.

   ...

   e55dd55
7. rchen152

   closed this as completedin e55dd55on Apr 17, 2019