simple question re list iteration semantics

[Esmail]

Hello all,

I have a simple question regarding semantics.

Given a list 'li', I can always do this to iterate through all items in
order:

for i in range(0, len(li)):
print li

Will this always be equivalent to


for i in li:
print i

I assume it is, and the order will always be the same, or am I mistaken?

Would the 2nd one be considered more Pythonic? (It looks both
clearer and cleaner to me).

Thanks.

Esmail

 

[Steven D'Aprano]

Given a list 'li', I can always do this to iterate through all items in
order:

for i in range(0, len(li)):
print li

Will this always be equivalent to

for i in li:
print i

For lists, yes, that will always be equivalent, and the second one is
considered more Pythonic.

 

[Paul Rubin]

for i in range(0, len(li)):
print li

Will this always be equivalent to


for i in li:
print i

Not the same--after the exit of the first loop, 'i' is the length of
the list. After the exit of the second loop, 'i' is the last element.

Would the 2nd one be considered more Pythonic? (It looks both
clearer and cleaner to me).

Yes. If you want to have the numeric index available in the loop, use:

for i,x in enumerate(li):
...

then i is the index and x is the element.

 

[Esmail]

for i in range(0, len(li)):
print li

Will this always be equivalent to


for i in li:
print i

Not the same--after the exit of the first loop, 'i' is the length of
the list. After the exit of the second loop, 'i' is the last element.

Yes, agreed.

If you want to have the numeric index available in the loop, use:

for i,x in enumerate(li):
...

then i is the index and x is the element.

ah .. very nice, I didn't know this -- thanks!

 

[Esmail]

for i in range(0, len(li)):
print li

Will this always be equivalent to


for i in li:
print i

Not the same--after the exit of the first loop, 'i' is the length of
the list. After the exit of the second loop, 'i' is the last element.

Yes, agreed.

If you want to have the numeric index available in the loop, use:

for i,x in enumerate(li):
...

then i is the index and x is the element.

ah .. very nice, I didn't know this -- thanks!