Asked By – alexis
Many Python programmers are probably unaware that the syntax of
while loops and
for loops includes an optional
for val in iterable: do_something(val) else: clean_up()
The body of the
else clause is a good place for certain kinds of clean-up actions, and is executed on normal termination of the loop: I.e., exiting the loop with
break skips the
else clause; exiting after a
continue executes it. I know this only because I just looked it up (yet again), because I can never remember when the
else clause is executed.
Always? On “failure” of the loop, as the name suggests? On regular termination? Even if the loop is exited with
return? I can never be entirely sure without looking it up.
I blame my persisting uncertainty on the choice of keyword: I find
else incredibly unmnemonic for this semantics. My question is not “why is this keyword used for this purpose” (which I would probably vote to close, though only after reading the answers and comments), but how can I think about the
else keyword so that its semantics make sense, and I can therefore remember it?
I’m sure there was a fair amount of discussion about this, and I can imagine that the choice was made for consistency with the
else: clause (which I also have to look up), and with the goal of not adding to the list of Python’s reserved words. Perhaps the reasons for choosing
else will clarify its function and make it more memorable, but I’m after connecting name to function, not after historical explanation per se.
The answers to this question, which my question was briefly closed as a duplicate of, contain a lot of interesting back story. My question has a different focus (how to connect the specific semantics of
else with the keyword choice), but I feel there should be a link to this question somewhere.
Now we will see solution for issue: How can I make sense of the `else` clause of Python loops?
while statement with an
while condition: suite else: exhausted
is exactly equivalent to
while True: if not condition: exhausted break suite
for statement with an
for item in iterable: suite else: exhausted
is exactly equivalent to
iterator = iter(iterable) try: while True: item = next(iterator) suite except StopIteration: exhausted
It helps understand the effect of a
continue statement in the suite statement.
Note. — For the
for statements without an
else clause, replace the exhausted statement with a
pass statement in the equivalent code.
To memorise the meaning of the
else clause, you can interpret a loop statement as
if loop_breaks: pass else: exhausted
This question is answered By – Maggyero
This answer is collected from stackoverflow and reviewed by FixPython community admins, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0