fix freqstr in BaseOffset being a property

[jkittner]

• Closes #xxxx (Replace xxxx with the Github issue number) [does not apply]
• Tests added: Please use assert_type() to assert the type of any return value

The freqstr is supposed to be a property, not a method returning a str

with this examples

from pandas import DateOffset

offset = DateOffset(minutes=10)
reveal_type(offset.freqstr)

and running mypy on this results in:

tt.py:4: note: Revealed type is "def () -> builtins.str"
Success: no issues found in 1 source file

with this patch it is properly captured as str:

tt.py:4: note: Revealed type is "builtins.str"
Success: no issues found in 1 source file

I ran into to this while doing this:

import pandas

delta = pandas.Timedelta(minutes=10)
offset = pandas.tseries.frequencies.to_offset(delta)

freq = None
if offset is not None:
    freq = offset.freqstr
    full_idx = pandas.date_range('2021', '2022', freq=freq)

tt.py:9: error: Argument "freq" to "date_range" has incompatible type "Callable[[], str]"; expected "Union[str, timedelta, Timedelta, BaseOffset]"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

I'd be happy to add a test for this, but I'm not sure how - maybe you can give me a hint. I tried this, but it passed both times, so does not capture the error where Offset becomes a Callable[[], str].

def test_freqstr() -> None:
    offset = DateOffset(minutes=10)
    check(assert_type(offset.freqstr, str), str)

[Dr-Irv]

I'd be happy to add a test for this, but I'm not sure how - maybe you can give me a hint. I tried this, but it passed both times, so does not capture the error where Offset becomes a Callable[[], str].

def test_freqstr() -> None:
    offset = DateOffset(minutes=10)
    check(assert_type(offset.freqstr, str), str)

The above test should work. If you remove your change, at least pyright picks up that assert_type will fail. mypy should do that as well, although I didn't test that.

Can you add the test, then I'll enable the CI test.

[jkittner]

thanks for looking into this! I added the test, but it passes also on main, so not verifying my fix.

[Dr-Irv]

Can you indicate how you tested it on main?

I did poetry run poe mypy and got this:

tests\test_timefuncs.py:1036: error: Expression is of type "Callable[[], str]", not "str"  [assert-type]

[jkittner]

oh I was just using pytest.

When using poetry run poe mypy I get an error on main but it's passing on freqstr-property so exactly what I want!

But with poetry run poe pytest everything is passing (like when I was just using pytest)
I was not aware how the tests are supposed to be run - sorry.

[Dr-Irv]

oh I was just using pytest.

When using poetry run poe mypy I get an error on main but it's passing on freqstr-property so exactly what I want!

But with poetry run poe pytest everything is passing (like when I was just using pytest) I was not aware how the tests are supposed to be run - sorry.

If you do poetry run poe test, it will run mypy, pyright and pytest. The first two do the type checking, which is what you are fixing. The last one checks that what we expect in the types is what happens at runtime. At runtime, assert_type(x, a) just returns x which is why it worked with pytest on main

[Dr-Irv]

thanks @theendlessriver13