不了解for循环中的if / else行为

Question

So I have a object with a method that is supposed to iterate over a list which is defined in the class.

When I use a simple if statement, I get the expected result, however, when I add an else statement I get strange results.

Class SomeClass(object):
     def __init__(self):
          self.config = ['something', 'this exists', 'some more stuff']

     def check_this(self):
          for line in self.config:
               if "this exists" in line:
                    return True

The above code returns True as soon as I get to the 2nd element in the list.

If I change the code to the following. The method returns False.

Class SomeClass(object):
     def __init__(self):
          self.config = ['something', 'this exists', 'some more stuff']

     def check_this(self):
          for line in self.config:
               if "this exists" in line:
                    return True
               else:
                    return False

I have to be missing something here. Python 2.7.6 on MAC OS X

Answer 1

In your latter case you never hit the 2nd element, because the 1st returns False . A function can only return one time.

In your first method, the only time it will return is if it get into your if block and will return True . If it never gets into the if block, it will return None .

In your second method, in the very first iteration, 'this exists' is not in line so it returns False and stops iterating.

If I understand the intention of that function, it could simply be

def check_this(self):
    return "this exists" in self.config

Answer 2

I think this is what you want:

 Class SomeClass(object):
      def __init__(self):
           self.config = ['something', 'this exists', 'some more stuff']

      def check_this(self):
          if "this exists" in self.config:
              return True
          else:
              return False