带有可变数学运算符的Python if语句 [英] Python if-statement with variable mathematical operator

问题描述

我试图在if语句中插入一个变量数学运算符，这是我试图解析用户提供的数学表达式的一个示例:

I'm trying to insert a variable mathematical operator into a if statement, an example of what I'm trying to achieve in parsing user-supplied mathematical expressions:

maths_operator = "=="

if "test" maths_operator "test":
       print "match found"

maths_operator = "!="

if "test" maths_operator "test":
       print "match found"
else:
       print "match not found"

显然，以上操作失败，并显示SyntaxError: invalid syntax.我已经尝试过使用exec和eval了，但是在if语句中都无法使用，我必须采取哪些解决方案?

obviously the above fails with SyntaxError: invalid syntax. I've tried using exec and eval but neither work in an if statement, what options do I have to get around this?

推荐答案

将operator包与字典一起使用，以根据它们的等效文本查找操作符.所有这些都必须是一元运算符或二进制运算符，才能一致地工作.

Use the operator package together with a dictionary to look up the operators according to their text equivalents. All of these must be either unary or binary operators to work consistently.

import operator
ops = {'==' : operator.eq,
       '!=' : operator.ne,
       '<=' : operator.le,
       '>=' : operator.ge,
       '>'  : operator.gt,
       '<'  : operator.lt}

maths_operator = "=="

if ops[maths_operator]("test", "test"):
    print "match found"

maths_operator = "!="

if ops[maths_operator]("test", "test"):
    print "match found"
else:
    print "match not found"

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