python - 为什么 python 不支持 : while( s = f. readline())？

Question

更多示例如下:

 if (a = xyz() ) > abc: 

真的很想知道为什么，是不是有点难闻？

注意:我知道语法，但我想问为什么 Python 不支持这种语法，而许多其他语言(例如，c、java...)支持

Answer 1

来自python design FAQ :

The reason for not allowing assignment in Python expressions is a common, hard-to-find bug in those other languages, caused by this construct:

    if (x = 0) {
        // error handling
    }
    else {
        // code that only works for nonzero x
    }

The error is a simple typo: x = 0, which assigns 0 to the variable x, was written while the comparison x == 0 is certainly what was intended.

如常见问题解答中所述，大多数在表达式中使用赋值的“用例”都可以通过使用迭代器来解决。