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Merged
merged 15 commits into from
May 25, 2022
Merged

TYP: Mypy workaround for NoDefault #47045

merged 15 commits into from
May 25, 2022

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twoertwein
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@twoertwein twoertwein commented May 17, 2022 •
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This uses the mypy-workaround from https://github.com/python/typeshed/pull/7127/files for NoDefault (works also for pyright).

no_default is public but NoDefault is luckily not public, so it should be fine to do the following:

  • rename the existing NoDefault to _NoDefault (implementation and typing)
  • define NoDefault as NoDefault = Literal[_NoDefault.no_default] (implementation and typing; isinstance checks need to be re-written to use is no_default but all other type annotations can stay the same)
  • no_default "remains" no_default = _NoDefault.no_default (just replacing NoDefault with _NoDefault)

@simonjayhawkins @jreback @Dr-Irv

edit:

Some context: The following will work without mypy errors afterwards:

def foo(x: NoDefault | int) -> int:
    if x is no_default:
        return -1
    return x + 1

@twoertwein twoertwein mentioned this pull request May 17, 2022
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@simonjayhawkins simonjayhawkins added the Typing type annotations, mypy/pyright type checking label May 18, 2022
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Something similar could also be done for NaT and NaTType

@twoertwein twoertwein marked this pull request as ready for review May 18, 2022 16:33
twoertwein
twoertwein commented May 18, 2022
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pandas/core/indexes/datetimes.py Outdated
@@ -1082,7 +1082,7 @@ def bdate_range(
name: Hashable = None,
weekmask=None,
holidays=None,
closed: lib.NoDefault = lib.no_default,
closed: Literal["left", "right"] | lib.NoDefault | None = lib.no_default,
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all the closed annotations seem unrelated but they are a result of this line

twoertwein
twoertwein commented May 18, 2022
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pandas/_libs/lib.pyx
@@ -2802,7 +2803,8 @@ class NoDefault(Enum):


# Note: no_default is exported to the public API in pandas.api.extensions
no_default = NoDefault.no_default # Sentinel indicating the default value.
no_default = _NoDefault.no_default # Sentinel indicating the default value.
NoDefault = Literal[_NoDefault.no_default]
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Instead of defining NoDefault in lib.pyx and lib.pyi it could be defined in _typing.py (would require changing a lot of import statements)

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its actually better where it is as we avoid circular deps this way

Dr-Irv
Dr-Irv reviewed May 24, 2022
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Two comments:

  1. There is a PEP for sentinel values: https://peps.python.org/pep-0661/ so if that PEP is approved, maybe we should use a pattern here that makes it easy for us to switch to using that feature if it gets approved.
  2. There is a lot of usage of Literal["left", "right"] in this PR, so maybe we should create a type for that in _typing.py and use that instead.

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1. There is a PEP for sentinel values:  https://peps.python.org/pep-0661/ so if that PEP is approved, maybe we should use a pattern here that makes it easy for us to switch to using that feature if it gets approved.

Once we can use this PEP (might take a long time, especially without typing_extensions), we simply need to change the two lines that define NoDefault and no_default on top of this PR (the PEP also encourages is for comparison, not isinstance). Technically, we would then need to change no_default when switching to this PEP which would technically break the API as it is a public symbol.

2. There is a lot of usage of `Literal["left", "right"]` in this PR,  so maybe we should create a type for that in `_typing.py` and use that instead.

Will do

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Dr-Irv commented May 24, 2022

Once we can use this PEP (might take a long time, especially without typing_extensions), we simply need to change the two lines that define NoDefault and no_default on top of this PR (the PEP also encourages is for comparison, not isinstance). Technically, we would then need to change no_default when switching to this PEP which would technically break the API as it is a public symbol.

OK, I see the path forward. However, while no_default is a public symbol, we don't document what it does, so I don't think changing it to be a sentinel will break anything. In any case, that is something that wouldn't need to be done for a few years.

Dr-Irv
Dr-Irv approved these changes May 24, 2022
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I'm fine with this, although I think others should approve as well.

@jreback jreback added this to the 1.5 milestone May 25, 2022
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jreback approved these changes May 25, 2022
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lgtm

@mroeschke mroeschke merged commit 1c82694 into pandas-dev:main May 25, 2022
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Thanks @twoertwein

@twoertwein twoertwein deleted the NoDefault branch May 26, 2022 01:58
yehoshuadimarsky pushed a commit to yehoshuadimarsky/pandas that referenced this pull request Jul 13, 2022
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TYP: Mypy workaround for NoDefault (pandas-dev#47045)
91f5786 
* TYP: NoDefault

* ix mypy issues; re-write isinstance(..., NoDefault)

* remove two more casts

* ENH: DatetimeArray fields support non-nano (pandas-dev#47044)

* DEPR: groupby numeric_only default (pandas-dev#47025)

* DOC: Clarify decay argument validation in ewm when times is provided (pandas-dev#47026)

* DOC: Fix some typos in pandas/. (pandas-dev#47022)

* remove two more casts

* avoid cast-like annotation

* left/right

* cannot use |

Co-authored-by: jbrockmendel <[email protected]>
Co-authored-by: Richard Shadrach <[email protected]>
Co-authored-by: Matthew Roeschke <[email protected]>
Co-authored-by: Shuangchi He <[email protected]>
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@jreback jreback jreback approved these changes

@mroeschke mroeschke mroeschke approved these changes

@Dr-Irv Dr-Irv Dr-Irv approved these changes

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@twoertwein @Dr-Irv @mroeschke @jreback @simonjayhawkins @jbrockmendel @rhshadrach @Yulv-git