Python - if语句中if语句在if循环中的中断

Question

这是一个有点令人困惑的问题，但这是我的(简化)代码。

if (r.status_code == 410):
     s_list = ['String A', 'String B', 'String C']
     for x in in s_list:
         if (some condition):
             print(x)
             break

     print('Not Found')

问题是，如果some condition是满意的(即x是打印的)，我不希望“Not”被打印。我怎样才能打破最外面的if语句？

Answer 1

不能脱离if语句；但是，可以使用for循环的else子句有条件地执行print调用。

if (r.status_code == 410):
     s_list = ['String A', 'String B', 'String C']
     for x in in s_list:
         if (some condition):
             print(x)
             break
     else:
         print('Not Found')

只有当for循环在迭代s_list时被StopIteration异常终止时，才会调用s_list，而不是当break语句终止它时。

Answer 2

为什么不直接使用变量呢？

if (r.status_code == 410):
     s_list = ['String A', 'String B', 'String C']
     found = None
     for x in in s_list:
         if (some condition):
             found = x
             print(x)
             break

     if not found:
         print('Not Found')

Answer 3

实际上，语言中有一种常见的机制，用于突破任何块，您抛出一个异常，只需确保捕捉到它并恢复流即可。这完全取决于你所处的环境(编码-标准、性能等)。

在某些语言中，它不像标签那样干净&跳转/转到，但我并不介意。

from builtins import Exception

class JumpingAround(Exception):
    def __init__(self, message=None, data=None, *args, **kwargs):
        super(Exception, self).__init__(message, *args, **kwargs)
        self.data = data

try: #surrounding the IF/BLOCK you want to jump out of
    if (r.status_code == 410):
        s_list = ['String A', 'String B', 'String C']
        for x in s_list:
            if (some condition):
                print(x)
                # break
                raise JumpingAround() # a more complex use case could raise JumpingAround(data=x) when catching in other functions 
        print('Not Found')
except JumpingAround as boing:
  pass