Ignoring types works differently in Python 3.8.13 than Python 3.9.13

[nbro10]

Bug Report

I'm trying to use # type: ignore to ignore certain false positives (errors) produced by mypy. In our project, I use multiple python versions, and, in particular, 3.8.13 and 3.9.13. I've noticed that mypy produces a different output for these 2 different versions of Python.

To Reproduce

Create the file main.py with the following contents

from pandas import DataFrame

data = DataFrame([[1, 2, 3], [3, 4, 5]], columns=["a", "b", "a"])
dup_columns_flags = data.columns.duplicated()

if dup_columns_flags.any():
    raise ValueError(
        f'data contains duplicated columns\n'  # type: ignore
        f'Columns: {data.columns.to_list()}\n'
        f'Duplicated columns: '
        f'{data.columns[dup_columns_flags].unique().to_list()}'
    )

Run mypy main.py with Python 3.8.13 and 3.9.13 and see that, in 3.9.13, the #type: ignore is not applicable to the whole fstring, but just the first line, while in 3.8.13 it seems to be applicable to the whole string. Of course, if I don't split the fstring into multiple lines, this doesn't happen.

In order to make mypy not report any error in 3.9.13, I need to do the following

from pandas import DataFrame

data = DataFrame([[1, 2, 3], [3, 4, 5]], columns=["a", "b", "a"])
dup_columns_flags = data.columns.duplicated()

if dup_columns_flags.any():
    raise ValueError(
        f'data contains duplicated columns\n'  
        f'Columns: {data.columns.to_list()}\n'  # type: ignore  
        f'Duplicated columns: '
        f'{data.columns[dup_columns_flags].unique().to_list()}'   # type: ignore  
    )

However, this does not work in Python 3.8.13. I would need also to place # type: ignore in front of the first line (like in the example above). So, in order to make this run in both versions, I need 3 comments, apparently

Expected Behavior

Mypy behaves in the same way in different python versions, if I am using the same dependencies

Actual Behavior

the opposite

Your Environment

• Mypy version used: 0.950
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files):

...
# Configs in the pyproject.toml
[tool.mypy]
python_version = 3.8
warn_return_any = true
warn_unused_configs = true
...

The behaviour above doesn't change if I use python_version = 3.9

• Python version used: 3.8.13 and 3.9.13

[erictraut]

I'm guessing that this is due to changes in the AST between Python 3.8 and 3.9.

In any case, I'm not able to repro the original problem even with older versions of mypy and Python 3.8 or Python 3.9. I'm not sure why a # type: ignore would be necessary here.

[hauntsaninja]

If Python AST has changed location information, this is a won't fix for mypy.

A common issue in cases like this is use of the --warn-unused-ignore setting, in which case you can use #8823 (comment)