Best way to have a for-loop index?

[andrewfelch]

I write a lot of code that looks like this:

for myElement, elementIndex in zip( elementList,
range(len(eleme ntList))):
print "myElement ", myElement, " at index: ",elementIn dex
My question is, is there a better, cleaner, or easier way to get at the
element in a list AND the index of a loop than this?

TIA,
Andrew

[Scott David Daniels]

an*********@gma il.com wrote:

I write a lot of code that looks like this:

for myElement, elementIndex in zip( elementList,
range(len(eleme ntList))):
print "myElement ", myElement, " at index: ",elementIn dex
My question is, is there a better, cleaner, or easier way to get at the
element in a list AND the index of a loop than this?

for elementIndex, myElement in enumerate(eleme ntList):
print "myElement ", myElement, " at index: ",elementIn dex
--Scott David Daniels
sc***********@a cm.org

[Michael Spencer]

an*********@gma il.com wrote:

I write a lot of code that looks like this:

for myElement, elementIndex in zip( elementList,
range(len(eleme ntList))):
print "myElement ", myElement, " at index: ",elementIn dex
My question is, is there a better, cleaner, or easier way to get at the
element in a list AND the index of a loop than this?

TIA,
Andrew

enumerate(itera ble)

Return an enumerate object. iterable must be a sequence, an iterator, or some
other object which supports iteration. The next() method of the iterator
returned by enumerate() returns a tuple containing a count (from zero) and the
corresponding value obtained from iterating over iterable. enumerate() is useful
for obtaining an indexed series: (0, seq[0]), (1, seq[1]), (2, seq[2]), .... New
in version 2.3

Michael

[Roy Smith]

In article <11************ ********@j33g20 00cwa.googlegro ups.com>,
an*********@gma il.com wrote:

I write a lot of code that looks like this:

for myElement, elementIndex in zip( elementList,
range(len(eleme ntList))):
print "myElement ", myElement, " at index: ",elementIn dex
My question is, is there a better, cleaner, or easier way to get at the
element in a list AND the index of a loop than this?

TIA,
Andrew

The real question is *why* do you want the index?

If you're trying to iterate through list indicies, you're probably trying
to write C, C++, Fortran, Java, etc in Python.

Can you describe exactly what it is that you're trying to do?

[Terry Hancock]

On 9 Mar 2006 16:32:24 -0800
an*********@gma il.com wrote:

I write a lot of code that looks like this:

for myElement, elementIndex in zip( elementList,
range(len(eleme ntList))):
print "myElement ", myElement, " at index:
",elementIn dex

My question is, is there a better, cleaner, or easier way
to get at the element in a list AND the index of a loop
than this?

In fact it is so common a need, there is a built-in
function called "enumerate" that does the 'zip' for
you:

for elementIndex, myElement in enumerate(eleme ntList):
print "myElement ", myElement, " at index: ",elementIn dex

--
Terry Hancock (ha*****@Anansi Spaceworks.com)
Anansi Spaceworks http://www.AnansiSpaceworks.com

[Steven D'Aprano]

On Thu, 09 Mar 2006 20:22:34 -0500, Roy Smith wrote:

My question is, is there a better, cleaner, or easier way to get at the
element in a list AND the index of a loop than this?

TIA,
Andrew

The real question is *why* do you want the index?

If you're trying to iterate through list indicies, you're probably trying
to write C, C++, Fortran, Java, etc in Python.

That's a bit harsh, surely? Well-meaning, but still harsh, and untrue.
Wanting to walk through a list replacing or modifying some or all items in
place is not unpythonic. Sure, you could simply create a new list:

L = [1, 2, 3, 4]
newL = []
for item in L:
if item % 3 == 0:
newL.append(ite m)
else:
newL.append(ite m**2)

but that's wasteful if the list is big, or if the items are expensive to
copy.

Isn't this more elegant, and Pythonic?

L = [1, 2, 3, 4]
for index, item in enumerate(L):
if item % 3 != 0:
L[index] = item**2

--
Steven.

[andrewfelch]

Sometimes C++ is the right tool/style for the job, but I don't need the
speed or efficiency of C++.

[nikie]

Roy Smith wrote:

In article <11************ ********@j33g20 00cwa.googlegro ups.com>,
an*********@gma il.com wrote:

I write a lot of code that looks like this:

for myElement, elementIndex in zip( elementList,
range(len(eleme ntList))):
print "myElement ", myElement, " at index: ",elementIn dex
My question is, is there a better, cleaner, or easier way to get at the
element in a list AND the index of a loop than this?

TIA,
Andrew

The real question is *why* do you want the index?

If you're trying to iterate through list indicies, you're probably trying
to write C, C++, Fortran, Java, etc in Python.

Interesting. I just wrote some tools today that parse through a bunch
of logfiles and print out something like: "unmatched memory allocation
in line XXX", or something like that. All of them have a main loop like
this:
for lineNumber, line in enumerate(file( "some.log") ): ...
I don't think there's anything wrong with that, is there a better way
to do it?
Personally, I don't think "enumerate" would be there if it always
encouraged an "unpythonic " programming style. But then again, I'm not
dutch, so I couldn't tell... ;-)

[Klaas]

roy spewed:

The real question is *why* do you want the index?

If you're trying to iterate through list indicies, you're probably trying
to write C, C++, Fortran, Java, etc in Python.

Could we stop the stupid continual beratement of people validly asking
about enumerate()? Yes, we want to discourage:

for i in xrange(len(seq) ):
seq[i]

but in this case, and many other cases, that is clearly not the
question being posed.

enumerate is one of the most useful built-ins and a love the way it
reads in code. Stop the index-hate.

-Mike