I understand how this construct works:
for i in range(10):
print(i)
if i == 9:
print("Too big - I'm giving up!")
break
else:
print("Completed successfully")
But I don't understand why else
is used as the keyword here, since it suggests the code in question only runs if the for
block does not complete, which is the opposite of what it does! No matter how I think about it, my brain can't progress seamlessly from the for
statement to the else
block. To me, continue
or continuewith
would make more sense (and I'm trying to train myself to read it as such).
I'm wondering how Python coders read this construct in their head (or aloud, if you like). Perhaps I'm missing something that would make such code blocks more easily decipherable?
This question is about the underlying design decision, i.e. why it is useful to be able to write this code. See also Else clause on Python while statement for the specific question about what the syntax means.
Best Answer
A common construct is to run a loop until something is found and then to break out of the loop. The problem is that if I break out of the loop or the loop ends I need to determine which case happened. One method is to create a flag or store variable that will let me do a second test to see how the loop was exited.
For example assume that I need to search through a list and process each item until a flag item is found and then stop processing. If the flag item is missing then an exception needs to be raised.
Using the Python
for
...else
construct you haveCompare this to a method that does not use this syntactic sugar:
In the first case the
raise
is bound tightly to the for loop it works with. In the second the binding is not as strong and errors may be introduced during maintenance.