Can't use _ in typeshed

[Dreamsorcerer]

As has been recommended as a workaround, I've tried using a custom typeshed directory to modify the builtins that Mypy sees, so that it recognises the _() function.

When adding to builtins.pyi:

from gettext import gettext
_ = gettext

I get:

error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.790
Traceback (most recent call last):
  File "mypy/semanal.py", line 4700, in accept
  File "mypy/nodes.py", line 1141, in accept
  File "mypy/semanal.py", line 3186, in visit_return_stmt
  File "mypy/nodes.py", line 1545, in accept
  File "mypy/semanal.py", line 3537, in visit_call_expr
  File "mypy/nodes.py", line 1545, in accept
  File "mypy/semanal.py", line 3454, in visit_call_expr
  File "mypy/nodes.py", line 1477, in accept
  File "mypy/semanal.py", line 3382, in visit_name_expr
  File "mypy/semanal.py", line 3895, in lookup
IndexError: string index out of range

Also, when I try:

from gettext import gettext as _

I don't get a crash, but Mypy still doesn't recognise it as a global function. Still producing dozens of:
error: Name '_' is not defined [name-defined]

[gvanrossum]

The problem is likely due to circular references -- clearly gettext.pyi depends on builtins.pyi (since every module does), so adding a dependency on gettext.pyi to builtins.pyi causes problems.

I'm sure you have already considered and rejected putting the import at the top of your own source files. I recommend reconsidering that, at least if you want static type checking to work for your code.

[Dreamsorcerer]

Actually, it works if I change it to:

from gettext import gettext
underscore = gettext

Still doesn't do anything with from gettext import gettext as underscore though.

So, seems that there may be several parts here:

• _ alone causes a crash
• names prefixed with _ don't appear (maybe Mypy sees them as private variables and doesn't export them even in builtins?).
• import as doesn't seem to work in builtins.

I could reconsider importing the function, I was just following what seemed to be recommended in the docs, e.g.:

For convenience, you want the _() function to be installed in Python’s builtins namespace, so it is easily accessible in all modules of your application.

https://docs.python.org/3/library/gettext.html#gettext.install
https://docs.python.org/3/library/gettext.html#localizing-your-application

[gvanrossum]

We should probably do something about those official recommendations of monkey-patching; we don't go around recommending from typing import * either. :-)