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TYP: annotate functions that always error with NoReturn #48002

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Merged
merged 1 commit into from
Aug 8, 2022
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TYP: annotate functions that always error with NoReturn #48002

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3 changes: 2 additions & 1 deletion pandas/core/groupby/ops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
Generic,
Hashable,
Iterator,
NoReturn,
Sequence,
final,
)
Expand Down Expand Up @@ -1243,7 +1244,7 @@ def groupings(self) -> list[grouper.Grouping]:
ping = grouper.Grouping(lev, lev, in_axis=False, level=None)
return [ping]

def _aggregate_series_fast(self, obj: Series, func: Callable) -> np.ndarray:
def _aggregate_series_fast(self, obj: Series, func: Callable) -> NoReturn:
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When we have NotImplementedError, does the NoReturn not create issues with subtypes? (in general, no checked this particular case)

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Yes it would create issues with sub-types that actually implement these functions. Parent methods should probably be abstract with a signature that the child will implement.

It should be safe adding NoReturn to final methods as no child class is meant to implement them. Based on the doc-string of _aggregate_series_fast I assume this method is basically deprecated and is not implemented in sub-classes.

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Thanks. yes it does appear that the exception is not for public consumption.

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NoReturn is useful in cases like this to narrow the type:

def error() -> NoReturn: ...

def test(x: int | str) -> str:
    # x: int | str
    if isinstance(x, int):
        error()
    # x: str
    return x + "some_string"

I don't there are many places where NoReturn can be used in pandas, in most cases we should make classes abstract.

Is there a historic reason to avoid inheriting from ABC and using abstractmethod? Happy to make PRs to make more methods abstract.

# -> np.ndarray[object]
raise NotImplementedError(
"This should not be reached; use _aggregate_series_pure_python"
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3 changes: 2 additions & 1 deletion pandas/core/indexes/base.py
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Expand Up @@ -12,6 +12,7 @@
Hashable,
Iterable,
Literal,
NoReturn,
Sequence,
TypeVar,
cast,
Expand Down Expand Up @@ -3166,7 +3167,7 @@ def __xor__(self, other):
return self.symmetric_difference(other)

@final
def __nonzero__(self):
def __nonzero__(self) -> NoReturn:
raise ValueError(
f"The truth value of a {type(self).__name__} is ambiguous. "
"Use a.empty, a.bool(), a.item(), a.any() or a.all()."
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7 changes: 5 additions & 2 deletions pandas/core/indexes/frozen.py
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Expand Up @@ -8,7 +8,10 @@
"""
from __future__ import annotations

from typing import Any
from typing import (
Any,
NoReturn,
)

from pandas.core.base import PandasObject

Expand Down Expand Up @@ -93,7 +96,7 @@ def __reduce__(self):
def __hash__(self) -> int: # type: ignore[override]
return hash(tuple(self))

def _disabled(self, *args, **kwargs):
def _disabled(self, *args, **kwargs) -> NoReturn:
"""
This method will not function because object is immutable.
"""
Expand Down