三元运算符的语法错误

问题描述

我是Python的新手，我正在尝试使用具有这种格式的三元运算符（我想是这样）

I'm new to Python and I'm trying to use ternary opertor which has this format (I think so)

value_true if <test> else value_false

下面是一段代码：

expanded = set()

while not someExpression:

    continue if currentState in expanded else expanded.push(currentState)

    # some code here

但是Python不喜欢它并说：

But Python doesn't like it and says:

SyntaxError: invalid syntax (pointed to if)

如何修复它？

推荐答案

Python中用于的三元运算表达式，而不是声明。表达式是有价值的东西。

Ternary operation in python using for expression, not statements. Expression is something that has value.

示例：

result = foo() if condition else (2 + 4)
#        ^^^^^                   ^^^^^^^
#      expression               expression

对于语句（如 continue ， for 之类的代码块） ，等等）使用 if ：

For statements (code blocks such as continue, for, etc) use if:

if condition:
     ...do something...
else:
     ...do something else...

您想做什么：

expanded = set()

while not someExpression:
    if currentState not in expanded: # you use set, so this condition is not really need
         expanded.add(currentState)
         # some code here

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