我想返回KeyError不是None

Question

I want to return KeyError but instead it returns None . I do not understand why.

if index == self.length or self.slots[index]==None:
    raise KeyError

Answer 1

You don't raise a KeyError because you don't enter the if -branch. And you don't enter the if -branch because none of your conditions is true .

You probably need to adjust your condition if the test-case (that you haven't shown!) should really raise the KeyError .

To debug this issue you can insert some print -statements:

print(index, self.length, index==self.length)
print(self.slots[index], self.slots[index]==None)
if index == self.length or self.slots[index]==None:
    raise KeyError

or use a debugger of your choice.

However some comments:

• Normally you want to check if the index is >= to the length (that includes == !).
• You should compare to None using is . None and NotImplemented are guaranteed singletons.
• Use an Exception message in KeyError , for example raise KeyError('index out of bounds or item is None! Try again.')
• Functions that don't have hit an explicit return will return None . That's probably why your code returned None instead!