Re: isPrime works but UnBoundLocalError when mapping on list

[Terry Reedy]

Andreas Tawn wrote:

Terry Reedy wrote:

>For loop variables continue after the loop exits. This is
intentional.

I never knew that and I can't find reference to it in the docs. Can you
help me with the reasons for it?

1. Python's reluctance to multiply scopes without necessity (as other
respondents have discussed).

2. This way, a for loop abbreviates an equivalent while loop (which does
have an explicit assignment). Something like:

for item in iterable:
suite

it = iter(iterable)
while True
item = next(it) # 3.0, 2.6?
suite

Of course, one could add 'del item' after the loop, but...

3. For search loops, the final value bound may be wanted after the loop.

for item in iterable:
if pred(item): break
else:
item = default
# item is now first item in iterable with property pred
# or fallback default.
f(item)

tjr