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ast.UnaryOp

expressions

Node for a unary operation: op is UAdd, USub, Not or Invert, operand is the expression it applies to.

Syntax

ast.UnaryOp(op, operand)

A negative number in source is not a Constant: -5 parses as UnaryOp(USub, Constant(5)), so analysis that looks for numbers via Constant loses the sign, even though ast.literal_eval accepts -5. Precedence is another trap: -2 ** 2 is a UnaryOp whose operand is the BinOp 2 ** 2, so the result is -4. Logical not is a UnaryOp too, while and/or are BoolOp.

Examples

import ast
n = ast.parse('-5', mode='eval').body
print(type(n).__name__, type(n.op).__name__, n.operand.value)  # → UnaryOp USub 5
print(ast.literal_eval('-5'))  # → -5

import ast
n = ast.parse('-2 ** 2', mode='eval').body
print(type(n).__name__, type(n.operand).__name__, -2 ** 2)  # → UnaryOp BinOp -4

See also

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