techalchemy commented on a change in pull request #4685: [AIRFLOW-3862] Check
types with mypy.
URL: https://github.com/apache/airflow/pull/4685#discussion_r257390078
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File path: setup.py
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@@ -319,6 +318,7 @@ def do_setup():
'sqlalchemy>=1.1.15, <1.3.0',
'tabulate>=0.7.5, <=0.8.2',
'tenacity==4.12.0',
+ 'typing',
Review comment:
hey, random stranger here -- I found this issue because I was trying to
typecheck my own airflow implementation and found that airflow itself doesn't
have published stubs, so that caused some issues. Just wanted to chime in and
say that type checking actually can be pretty slow, which is why python 3.7
even introduced a `__future__` import to perform lazy typechecking imports.
See [PEP 563](https://www.python.org/dev/peps/pep-0563) for reference.
What's more, you can't put typechecking imports behind a conditional unless
you actually have `typing` installed in the first place to check whether the
typechecker is running. The conventional approach is to just use
`'typing;python_version<"3.5"'` as your constraint.
The alternative approach is to do this (I actually do both personally but in
theory you can pick one):
```python
def is_type_checking():
try:
from typing import TYPE_CHECKING
except ImportError:
return False
return TYPE_CHECKING
MYPY_RUNNING = is_type_checking()
```
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