gh-130959: Reject whitespace in fractions, in pure Python fromisoformat() (#130962)

* gh-130959: Reject whitespace in fractions, in pure Python `fromisoformat()`

Fix the pure Python implementation of `fromisoformat()` to reject any
non-digit characters, including whitespace, in the fractional part
of time specification.  This makes the behavior consistent with the C
implementation, and prevents incorrect parsing of these fractions
(e.g. `.400 ` would be misinterpreted as `.04`).

* Add the news entry

* Use a different example to fix Sphinx lint

* Apply suggestions from code review

Co-authored-by: Peter Bierma <[email protected]>
Co-authored-by: Paul Ganssle <[email protected]>

* Try fixing `:func:` ref.

---------

Co-authored-by: Peter Bierma <[email protected]>
Co-authored-by: Paul Ganssle <[email protected]>

Author: 3 people

Lib/_pydatetime.py

@@ -436,6 +436,8 @@ def _parse_hh_mm_ss_ff(tstr):
             raise ValueError("Invalid microsecond separator")
         else:
             pos += 1
+            if not all(map(_is_ascii_digit, tstr[pos:])):
+                raise ValueError("Non-digit values in fraction")
 
             len_remainder = len_str - pos
 
@@ -447,9 +449,6 @@ def _parse_hh_mm_ss_ff(tstr):
             time_comps[3] = int(tstr[pos:(pos+to_parse)])
             if to_parse < 6:
                 time_comps[3] *= _FRACTION_CORRECTION[to_parse-1]
-            if (len_remainder > to_parse
-                    and not all(map(_is_ascii_digit, tstr[(pos+to_parse):]))):
-                raise ValueError("Non-digit values in unparsed fraction")
 
     return time_comps
 

Lib/test/datetimetester.py

@@ -3556,6 +3556,9 @@ def test_fromisoformat_fails_datetime(self):
             '9999-12-31T24:00:00.000000',  # Year is invalid after wrapping due to 24:00
             '2009-04-19T12:30Z12:00',      # Extra time zone info after Z
             '2009-04-19T12:30:45:334034',  # Invalid microsecond separator
+            '2009-04-19T12:30:45.400 +02:30',  # Space between ms and timezone (gh-130959)
+            '2009-04-19T12:30:45.400 ',        # Trailing space (gh-130959)
+            '2009-04-19T12:30:45. 400',        # Space before fraction (gh-130959)
         ]
 
         for bad_str in bad_strs:
@@ -4773,6 +4776,9 @@ def test_fromisoformat_fails(self):
             '12:30,5',                  # Decimal mark at end of minute
             '12:30:45.123456Z12:00',    # Extra time zone info after Z
             '12:30:45:334034',          # Invalid microsecond separator
+            '12:30:45.400 +02:30',      # Space between ms and timezone (gh-130959)
+            '12:30:45.400 ',            # Trailing space (gh-130959)
+            '12:30:45. 400',            # Space before fraction (gh-130959)
         ]
 
         for bad_str in bad_strs:

Misc/NEWS.d/next/Library/2025-03-07-19-24-27.gh-issue-130959.xO8vVS.rst

@@ -0,0 +1,3 @@
+Fix pure-Python implementation of :func:`datetime.time.fromisoformat` to reject
+times with spaces in fractional part (for example, ``12:34:56.400 +02:00``),
+matching the C implementation. Patch by Michał Gorny.