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Comment by montebicyclelo | Hacker News Reader

What's the advantage over the following?:

  for i in range(n):
      if search(i) == val:
          break
      raise KeyError("not found")
  found_index = i

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That version doesn't work. It raises KeyError on the first iteration if the if statement is false.

The point of the for / else is that the else only gets evaluated when the for terminates without a break. So in the example you only get a KeyError if the search() never returns val.

Part of the confusion I guess is that the else: in my example is paired with for, not with if, Python indentation being significant etc.

Aha, thank you. Yes, it's plausible that my brain did pair the `else` with the `if`, even though it knew it was supposed to be paired with the `for`.

Before being introduced to `for`/`else`, I'd have written the example you gave as:

  result = None
  for i in range(n):
      if search(i) == val:
          result = i
  if not result:
      raise KeyError("not found")

I think this snippet would raise a KeyError whenever the index you're searching for is greater than 0.

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