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Dutcho opened this issue Jul 23, 2023 · 4 comments
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help() output of lambda with manually set __annotations__ is one char off #107155

Dutcho opened this issue Jul 23, 2023 · 4 comments
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3.11 only security fixes 3.12 only security fixes 3.13 bugs and security fixes stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@Dutcho
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Dutcho commented Jul 23, 2023 •
edited by bedevere-app bot
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Bug report

help() output of lambda with manually set __annotations__ is slightly scrambled.

f = lambda a, b, c: 0              # lambdas cannot have annotations
f.__annotations__['return'] = int  # but you can set them manually

help(f)                            # superfluous ")" and missed last char
# <lambda> lambda a, b, c) -> in

import inspect
print(inspect.signature(f))        # correctly displays
# (a, b, c) -> int

Note

This is a minor glitch for an atypical (perhaps even unsupported) use of annotations.

Hypothesis

Perhaps help() uses (the same logic as) inspect.signature() and (to reflect lambda syntax) wants to drop the brackets "(...)", but then has a one-off error for its text slice (picking ") -> in" instead of " -> int")

Environment

  • CPython versions tested on: 3.6.8 - 3.11.4, 3.12.0b4
  • Operating system and architecture: Windows 11

Linked PRs
@Dutcho Dutcho added the type-bug An unexpected behavior, bug, or error label Jul 23, 2023
@AlexWaygood AlexWaygood added the stdlib Python modules in the Lib dir label Jul 23, 2023
@Eclips4
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Eclips4 commented Jul 25, 2023

Looks like a known issue :)

cpython/Lib/pydoc.py

Lines 1503 to 1506 in f443b54

# XXX lambda's won't usually have func_annotations['return']
# since the syntax doesn't support but it is possible.
# So removing parentheses isn't truly safe.
argspec = argspec[1:-1] # remove parentheses

@Eclips4
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Eclips4 commented Jul 25, 2023 •
edited
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Probably, we can just replace boundaries, argspec.replace("(", "").replace(")", ""). Can there be any parenthesis in signature of lambda?

Eclips4 added a commit to Eclips4/cpython that referenced this issue Jul 28, 2023
@Eclips4
pythongh-107155: Fix help(lambda_func) when lambda_func has `__an…
d0d69c2 
…notations__` with `return` key.
@bedevere-bot bedevere-bot mentioned this issue Jul 28, 2023
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@AA-Turner
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f = lambda a, b: (a, b)
f.__annotations__['return'] = (int, int)
help(f)
# Help on function <lambda> in module __main__:
#
# <lambda> lambda a, b) -> (<class 'int'>, <class 'int'>

This isn't currently a legal type annotation, but using tuple literals was proposed in PEP-677 and something similar could come up again -- a cleaner fix could be to handle the string conversion manually. I've suggested something on the PR.

A

@AA-Turner AA-Turner added 3.13 bugs and security fixes 3.11 only security fixes 3.12 only security fixes labels Jul 30, 2023
@serhiy-storchaka
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The parentheses were removed because lambda (a, b, c) is not a valid Python syntax. But neither lambda a, b, c -> int is. So why simply not keep parentheses if there are annotations? lambda (a, b, c) -> int. It will also be less ambiguous if parameters are annotated: lambda (a: int, b: int, c: int) -> int.

serhiy-storchaka pushed a commit that referenced this issue Feb 17, 2024
@Eclips4
gh-107155: Fix help() for lambda function with return annotation (GH-…
b9a9e3d 
…107401)
@bedevere-app bedevere-app bot mentioned this issue Feb 17, 2024
Merged
Eclips4 added a commit to Eclips4/cpython that referenced this issue Feb 17, 2024
@Eclips4
[3.12] pythongh-107155: Fix help() for lambda function with return an…
eec85e8 
…notation (pythonGH-107401)

(cherry picked from commit b9a9e3d)

Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>
@bedevere-app bedevere-app bot mentioned this issue Feb 17, 2024
Merged
serhiy-storchaka pushed a commit that referenced this issue Feb 17, 2024
@Eclips4
[3.12] gh-107155: Fix help() for lambda function with return annotati…
e32cde5 
…on (GH-115612)

(cherry picked from commit b9a9e3d)
serhiy-storchaka pushed a commit that referenced this issue Feb 17, 2024
@Eclips4
[3.11] gh-107155: Fix help() for lambda function with return annotati…
ee3d8dc 
…on (GH-115613)

(cherry picked from commit b9a9e3d)
woodruffw pushed a commit to woodruffw-forks/cpython that referenced this issue Mar 4, 2024
@Eclips4 @woodruffw
pythongh-107155: Fix help() for lambda function with return annotation (
cdd5ee9 
pythonGH-107401)
diegorusso pushed a commit to diegorusso/cpython that referenced this issue Apr 17, 2024
@Eclips4 @diegorusso
pythongh-107155: Fix help() for lambda function with return annotation (
4561a2c 
pythonGH-107401)
LukasWoodtli pushed a commit to LukasWoodtli/cpython that referenced this issue Jan 22, 2025
@Eclips4 @LukasWoodtli
pythongh-107155: Fix help() for lambda function with return annotation (
cc7b57e 
pythonGH-107401)
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@serhiy-storchaka @Dutcho @AA-Turner @AlexWaygood @Eclips4