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ast.Sub

operators

The subtraction operator - in the op field of BinOp and AugAssign nodes.

Syntax

ast.Sub()

Sub is only the binary minus: -x parses as UnaryOp(USub). Subtraction is left-associative, so a - b - c is a BinOp with the nested BinOp on the left and just c on the right. The parser reuses one Sub object for every occurrence, so compare with isinstance(node.op, ast.Sub), not node.op == ast.Sub().

Examples

import ast
n = ast.parse('a - b - c', mode='eval').body
print(type(n.op).__name__, type(n.left).__name__, n.right.id)  # → Sub BinOp c
print(type(ast.parse('-x', mode='eval').body.op).__name__)  # → USub

import ast
a = ast.parse('x - y', mode='eval').body.op
b = ast.parse('p - q', mode='eval').body.op
print(a is b, a == ast.Sub(), isinstance(a, ast.Sub))  # → True False True

See also

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