pprint.isreadable returns True for non-eval-able float and complex specials

[zetzschest]

Issue

isreadable is documented as returning True if the object's repr is readable by the interpreter — implying eval(pformat(obj)) == obj. For float and complex non-finite values, isreadable returns True, but the roundtrip fails — eval raises NameError since inf and nan aren't valid Python expressions.

Reproducer

import pprint

print(pprint.isreadable(float('inf')))        # True — but eval('inf') raises NameError
print(pprint.isreadable(float('nan')))        # True
print(pprint.isreadable(complex(float('inf'), 0)))  # True

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-145117: Fix pprint.isreadable() returning True for inf/nan #145116
• gh-145117: fix pprint.isreadable() for non-finite float and complex values #145120

[skirpichev]

I would say it's a documentation issue. It affects also complex numbers:

>>> pprint.isreadable(complex('inf'))
True

We also have "broken" eval(repr(x)) == x invariant for x=inf, unless you add missing import from the math module.