"Weird" Indentation? (Or: is there a for...else construct?)

[Andreas Waldenburger]

I've found something in the spirit of the following (in the epydoc
sources, if you care):

if True:
print "outer if"
for t in range(2):
if True:
print "for if"
else:
print "phantom else"

For the life of me I can't place the "else". Which if clause does it
belong to? None, it would seem from running the above snippet:

outer if
For if
For if
Phantom else

It seems that there is a for...else construct. Replacing the inner if
with pass seems to confirm this. The else clause is still executed.

What's broken here: Python or my brain?

/W

 

[Andreas Waldenburger]

outer if
For if
For if
Phantom else

Geez, I'm a moron. This is obviously not the output from the snippet.
But if you fix the capitalization, it is. Sorry for that.

/W

 

[Steven D'Aprano]

It seems that there is a for...else construct. Replacing the inner if
with pass seems to confirm this. The else clause is still executed.

Yes, there is a for...else construct.

The else block runs if the for loop exits *without* a break.

for i in range(20):
if i == 10: break
else:
print "no break here"

for i in range(20):
if i == 100: break
else:
print "no break here"

What's broken here: Python or my brain?

Perhaps we should not answer that question.

 

[Peter Otten]

I've found something in the spirit of the following (in the epydoc
sources, if you care):

if True:
print "outer if"
for t in range(2):
if True:
print "for if"
else:
print "phantom else"

For the life of me I can't place the "else". Which if clause does it
belong to? None, it would seem from running the above snippet:

outer if
For if
For if
Phantom else

It seems that there is a for...else construct. Replacing the inner if
with pass seems to confirm this. The else clause is still executed.

What's broken here: Python or my brain?

Your rtfm sensor?

http://docs.python.org/reference/compound_stmts.html#the-for-statement

In short, the else suite is executed unless the for-loop is left
via 'break':

for i in [1]:

.... break
.... else:
.... print "else"
....

for i in [1]:

.... pass
.... else:
.... print "else"
....
else
Peter

 

[Andreas Waldenburger]

Yes, there is a for...else construct.

That's something. In 6+ years of Python programming I've never seen or
heard of this thing. This might be useful, apparently.

[snip]

What's broken here: Python or my brain?

Perhaps we should not answer that question.

I did phrase that rather provocatively, didn't I?

Well thanks. I'll try to learn less noisily in the future.

/W

 

[MRAB]

That's something. In 6+ years of Python programming I've never seen or
heard of this thing. This might be useful, apparently.

One use case is:

for x in list_of_items:
if x.value == desired_value:
desired_name = x.name
break
else:
print "Couldn't find %s" % x.value

[snip]

What's broken here: Python or my brain?

Perhaps we should not answer that question.

I did phrase that rather provocatively, didn't I?

Well thanks. I'll try to learn less noisily in the future.

 

[Diez B. Roggisch]

Your rtfm sensor?

http://docs.python.org/reference/compound_stmts.html#the-for-statement

In short, the else suite is executed unless the for-loop is left
via 'break':

Or exceptions of course. Might be obvious, but for completeness' sake.

Diez

 

[Tim Rowe]

there's a justification for this awful mess here -
http://mail.python.org/pipermail/python-3000/2006-March/000104.html

i didn't know about this, and even after reading steven's broken (i
assume) example, managed to get it backwards.

What's awful about it? Except in the sense of inspiring awe, of
course. No, Steven's example isn't broken, it works as the epydoc
authors intended.

(it's still in 3).

Good.

 

[birdsong]

That's something. In 6+ years of Python programming I've never seen or
heard of this thing. This might be useful, apparently.

yeah, about 4 years for me and i've never noticed this feature.

[snip]

What's broken here: Python or my brain?

Perhaps we should not answer that question.

I did phrase that rather provocatively, didn't I?

Well thanks. I'll try to learn less noisily in the future.

/W