The general solution is import typing if typing.TYPE_CHECKING: <whatever> The hack of starting with TYPE_CHECKING = False happens to work but is not endorsed by PEP 484 so is not guaranteed for the future. Note that 3rd party code is rarely in such a critical part for script startup that the cost of `import typing` is too much. But the stdlib often *is* in the critical path for script startup, and some consider the time spent in that import too much (startup time should be in the order of tens of msec so every msec counts -- but once you start importing 3rd party code you basically can't make it that fast regardless). Anyway, the stdlib should almost never be used as an example for non-stdlib code -- there are many reasons for this that I don't want to have to repeat here. On Tue, Apr 23, 2019 at 12:33 PM Ilya Kamenshchikov < ikamenshchikov@gmail.com> wrote:
How would we answer the same question if it was not a part of stdlib? I am not sure it is fair to expect of Pycharm to parse / execute the __getattr__ on modules, as more elaborate implementation could even contain different types per some condition at the runtime or anything at all. The code:
TYPE_CHECKING = False if TYPE_CHECKING: from .process import ProcessPoolExecutor from .thread import ThreadPoolExecutor
works for type checking in PyCharm and is fast.
This is how stdlib can be an example to how side libraries can be implemented. If we can agree that this is the only clear, performant and sufficient code - then perhaps modifying mypy is a reasonable price to pay.
Perhaps this particular case can be just patched locally by PyCharm /JetBrains, but what is a general solution to this class of problems?
Best Regards, -- Ilya Kamenshchikov
On Tue, Apr 23, 2019 at 7:05 PM Guido van Rossum <guido@python.org> wrote:
In any case I think this should be filed (by the OP) as an issue against JetBrains' PyCharm issue tracker. Who knows they may be able to special-case this in a jiffy. I don't think we should add any clever hacks to the stdlib for this.
On Tue, Apr 23, 2019 at 9:59 AM Nathaniel Smith <njs@pobox.com> wrote:
On Tue, Apr 23, 2019, 05:09 Andrew Svetlov <andrew.svetlov@gmail.com> wrote:
I agree that `from typing import TYPE_CHECKING` is not desirable from the import time reduction perspective.
From my understanding code completion *can* be based on type hinting to avoid actual code execution. That's why I've mentioned that typeshed already has the correct type information.
if TYPE_CHECKING: import ...
requires mypy modification.
if False: import ...
Works right now for stdlib (mypy ignores stdlib code but uses typeshed anyway) but looks a little cryptic. Requires a comprehensive comment at least.
Last time I looked at this, I'm pretty sure `if False` broke at least one popular static analysis tool (ie it was clever enough to ignore everything inside `if False`) – I think either pylint or jedi?
I'd suggest checking any clever hacks against at least: mypy, pylint/astroid, jedi, pyflakes, and pycharm. They all have their own static analysis engines, and each one has its own idiosyncratic quirks.
We've struggled with this a *lot* in trio, and eventually ended up giving up on all forms of dynamic export cleverness; we've even banned the use of __all__ entirely. Static analysis has gotten good enough that users won't accept it not working, but it hasn't gotten good enough to handle anything but the simplest static exports in a reliable way: https://github.com/python-trio/trio/pull/316 https://github.com/python-trio/trio/issues/542
The stdlib has more leeway because when tools don't work on the stdlib then they tend to eventually add workarounds. I'm just saying, think twice before diving into clever hacks to workaround static analysis limits, and if you're going to do it then be careful to be thorough. You're basically relying on undocumented bugs, and it gets really messy really quickly.
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-- --Guido van Rossum (python.org/~guido) *Pronouns: he/him/his **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
-- --Guido van Rossum (python.org/~guido) *Pronouns: he/him/his **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>