Fix: In fire/parser.py's _LiteralEval, the AST walk replaces bare ast.Name... - #694
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M001N wants to merge 1 commit into
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Fix: In fire/parser.py's _LiteralEval, the AST walk replaces bare ast.Name...#694M001N wants to merge 1 commit into
M001N wants to merge 1 commit into
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DefaultParseValue('[a,-b,c]') previously fell back to treating the
whole value as a plain string, because the bareword-replacement AST
walk in _LiteralEval replaced the inner Name node of
UnaryOp(USub, Name('b')) with a string Constant, leaving an invalid
UnaryOp(USub, Constant('b')) that ast.literal_eval rejects.
Now the walk detects a UnaryOp(USub, Name) -- i.e. a unary minus
applied to a bare identifier -- and replaces the whole UnaryOp node
with a single string Constant '-' + name, so it parses as the string
'-b' instead. Numeric negation (UnaryOp(USub, Constant(2))) is
untouched and still evaluates to the int -2.
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Summary
Added a helper _IsNegativeBareword(node) that detects ast.UnaryOp(USub, Name) where the Name isn't True/False/None. In the existing bareword-replacement walk (both the list-field branch and the single-field branch), when a child matches this pattern, the ENTIRE UnaryOp node is replaced with a string Constant of '-' + the identifier name (e.g. '-b'), instead of only replacing the inner Name. Genuine numeric negation (UnaryOp(USub, Constant(2))) doesn't match the pattern (operand is Constant, not Name) and is left untouched, so ast.literal_eval still evaluates it as int -2.
Problem
google/python-fire issue reference: #229
Root Cause
In fire/parser.py's _LiteralEval, the AST walk replaces bare ast.Name nodes with string ast.Constant nodes to support YAML-like unquoted-string syntax. For the token '-b', the parser produces ast.UnaryOp(op=USub, operand=ast.Name('b')). The walk replaced only the inner Name('b') with Constant('b'), leaving UnaryOp(USub, Constant('b')) -- an invalid 'negative string' expression that ast.literal_eval rejects with ValueError. DefaultParseValue's outer except then discarded all list structure and returned the raw input string.
Testing
PASS for parser_test.py (21/21 passed, including new test covering '[a,-b,c]' -> ['a','-b','c'], '[1,-2,3]' -> [1,-2,3] with -2 as int, and standalone '-b' -> '-b'). Full suite: 260 passed, 2 failed, but both failures (main_test.py::MainModuleTest::testArgPassing, main_test.py::MainModuleFileTest::testFileNameFire) are pre-existing, unrelated Windows-environment issues (regex pattern error and a PermissionError writing to a Windows temp file during module import) with no connection to parser.py.
Related Issue
#229