给定这些字符串:
"1 + 2"
"apple,pear"
如何使用 Python 3(.5) 确定第一个字符串包含数学问题并且没有其他的而第二根弦没有?
这是一种方法:
import ast
UNARY_OPS = (ast.UAdd, ast.USub)
BINARY_OPS = (ast.Add, ast.Sub, ast.Mult, ast.Div, ast.Mod)
def is_arithmetic(s):
def _is_arithmetic(node):
if isinstance(node, ast.Num):
return True
elif isinstance(node, ast.Expression):
return _is_arithmetic(node.body)
elif isinstance(node, ast.UnaryOp):
valid_op = isinstance(node.op, UNARY_OPS)
return valid_op and _is_arithmetic(node.operand)
elif isinstance(node, ast.BinOp):
valid_op = isinstance(node.op, BINARY_OPS)
return valid_op and _is_arithmetic(node.left) and _is_arithmetic(node.right)
else:
raise ValueError('Unsupported type {}'.format(node))
try:
return _is_arithmetic(ast.parse(s, mode='eval'))
except (SyntaxError, ValueError):
return False
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