嵌套的“和/或"如果陈述 [英] nested "and/or" if statements

问题描述

我正在研究创建列表的代码，然后同时应用或"和与"条件来执行进一步的操作:

I am working on code which creates a list and then applies both the "or" and "and" conditions to do further action:

a= ["john", "carlos", "22", "70"]

if (("qjohn" or "carlos") in a) and (("272" or "70") in a):
    print "true"
else:
    print "not true"

输出:

not true

当我这样做时:

a= ["john", "carlos", "22", "70"]

if ("qjohn" or "cdarlos" in a) and ("272" or "d70" in a):
    print "true"
else:
    print "not true"

输出为"true"

我没有得到的是**carlos and 70**应该等于true，但是它打印的是"not true".此错误的原因是什么?谢谢

What I am not getting is **carlos and 70** should be equal to true but it's printing "not true". What is the cause of this error? Thanks

推荐答案

两种方法都不正确.请记住，或是短路运算符，因此它没有按照您的预期做:

Both approaches are incorrect. Keep in mind or is a short-circuit operator so it's not doing what you think it does:

仅在第一个参数为false时才评估第二个参数.

it only evaluates the second argument if the first one is false.

但是，非空字符串始终为True，因此第一种情况仅检查第一个非空字符串的包含，而第二种情况根本不使用in进行容纳检查，因此，它始终为True.

However, non-empty strings are always True, so that the first case only checks for the containment of the first non-empty string while the second never performs the containment check with in at all, therefore, it is always True.

您想要的是:

if ("qjohn" in a or "carlos" in a) and ("272"  in a or "70" in a):
   ...

如果要测试的项目较长，则可以使用any避免重复or，就像or一样，一旦其中一项测试True也会短路:

If the items to test were longer, you could avoid repeating the or by using any which like or also short-circuits once one of the items test True:

if any(x in a for x in case1) and any(x in a for x in case2):
   ...

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