fuzz findings [python]: undeclared disagreements (2026-08-23)

[zmaril]

Fuzzing derived programs the grammar and the reference parser disagree on.

• findings: 115 (108 undeclared)
• iterations: 5000
• we_accepted: 1178
• we_rejected: 2696
• agreed: 337
• widenings: 841
• grammar coverage: 97.5% of alternatives

Undeclared programs the reference parser accepts but our grammar splits differently (108 distinct):

( ) : XX

[ ] : XX

* XX : XX

XX , : XX

yield pass

---

Filed automatically by piecework.
lang: python · kind: fuzz · grammar: 7d157a1 · corpus depth: 1915 packages
ticket: fuzz-python-403399968 (exit 0)

job log tail

ning: invalid escape sequence '\ '
  del " s " " " " { a } \ " ( ) [ : : ] ,
/tmp/treebank-fuzz-2492857/probe0.py:2: SyntaxWarning: invalid escape sequence '\ '
/tmp/treebank-fuzz-2492857/probe1.py:2: SyntaxWarning: invalid escape sequence '\ '
  if " { a if a else a = } " " s \ " " { yield = : } " if XX | XX else XX : XX
/tmp/treebank-fuzz-2492857/probe0.py:1: SyntaxWarning: invalid escape sequence '\ '
  del " s " " " " { a } \ " ( ) [ : : ] ,
/tmp/treebank-fuzz-2492857/probe0.py:2: SyntaxWarning: invalid escape sequence '\ '
/tmp/treebank-fuzz-2492857/probe0.py:2: SyntaxWarning: invalid escape sequence '\ '
/tmp/treebank-fuzz-2492857/probe2.py:2: SyntaxWarning: invalid escape sequence '\ '
  
/tmp/treebank-fuzz-2492857/probe0.py:1: SyntaxWarning: invalid escape sequence '\ '
  del " s " " " " { a } \ " ( ) [ : : ] ,
/tmp/treebank-fuzz-2492857/probe0.py:1: SyntaxWarning: invalid escape sequence '\ '
  del " s " " " " { a } \ " ( ) [ : : ] ,
fuzz: 1178 accepted by us (2696 discarded as unfaithful), 337 agreed, 841 widening(s) in 115 distinct program(s) — 108 undeclared, 7 declared
  (7 declared by fuzz_policy.toml)
fuzz: coverage — 635/651 grammar alternatives (97.5%), 163 tape(s) kept
  unreached   10  in _params_slash_nodefault_rest
  unreached    4  in _lambda_params_slash_nodefault_rest
  unreached    1  in _case_sequence
  unreached    1  in _params_keyword_rest
    1x  ( ) : XX ⏎ 
    1x  [ ] : XX ⏎ 
    1x  * XX : XX ⏎ 
    7x  XX , : XX ⏎ 
    1x  yield pass ⏎ 
    1x  * * XX = XX ⏎ 
    1x  XX := XX ⏎ XX ⏎ 
    2x  return pass ⏎ 
    1x  del [ * XX ] ⏎ 
    4x  return yield ⏎ 
    1x  XX += XX = XX ⏎ 
    1x  del XX , break ⏎ 
    1x  del ` XX ` . XX ⏎ 
    1x  pass ; ⏎ print XX ⏎ 
    1x  return yield ⏎ XX ⏎ 
    2x  XX += XX = XX ⏎ XX ⏎ 
    1x  del XX ; ⏎ exec XX ⏎ 
    1x  0x0_0l . XX += XX ⏎ 
    1x  ` XX ` . XX += XX ⏎ 
    1x  del { yield } . XX ⏎ 
fuzz: report at corpus/python/reports/fuzz.json