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

• gh-107155: Fix help(lambda_func) when lambda_func has `__annotati… #107401
• [3.12] gh-107155: Fix help() for lambda function with return annotati… #115612
• [3.11] gh-107155: Fix help() for lambda function with return annotati… #115613