gh-145117: fix pprint.isreadable() for non-finite float and complex values

Lib/pprint.py

@@ -34,6 +34,7 @@
 
 """
 
+import cmath as _cmath
 import collections as _collections
 import sys as _sys
 import types as _types
@@ -627,7 +628,10 @@ def _safe_repr(self, object, context, maxlevels, level):
         # Return triple (repr_string, isreadable, isrecursive).
         typ = type(object)
         if typ in _builtin_scalars:
-            return repr(object), True, False
+            rep = repr(object)
+            if (typ is float or typ is complex) and not _cmath.isfinite(object):
+                return rep, False, False
+            return rep, True, False
 
         r = getattr(typ, "__repr__", None)
 

Lib/test/test_pprint.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import cmath
 import collections
 import contextlib
 import dataclasses
@@ -182,6 +183,19 @@ def test_basic(self):
             self.assertTrue(pp.isreadable(safe),
                             "expected isreadable for %r" % (safe,))
 
+    def test_isreadable_float_specials(self):
+        # inf, -inf, nan are not valid Python literals so isreadable should be False
+        # same applies to complex numbers with non-finite components
+        non_finite = (float("inf"), float("-inf"), float("nan"))
+        for v in (*non_finite,
+                  *(complex(x, y) for x in (*non_finite, 0)
+                                  for y in (*non_finite, 0)
+                                  if not cmath.isfinite(complex(x, y)))):
+            self.assertFalse(pprint.isreadable(v),
+                             "expected not isreadable for %r" % (v,))
+            self.assertFalse(pprint.PrettyPrinter().isreadable(v),
+                             "expected not isreadable for %r" % (v,))
+
     def test_stdout_is_None(self):
         with contextlib.redirect_stdout(None):
             # smoke test - there is no output to check

Misc/NEWS.d/next/Library/2026-02-22-00-00-00.gh-issue-145117.pPrint.rst

@@ -0,0 +1,5 @@
+Fix :func:`pprint.isreadable` to return ``False`` for non-finite :class:`float`
+and :class:`complex` values (``inf``, ``-inf``, ``nan`` and complex numbers with
+non-finite components). Their string representations are not valid Python
+expressions and cannot be reconstructed via :func:`eval`, violating the
+documented contract of :func:`~pprint.isreadable`.