Python - Default Counter Variable in For loop

Question

Is there any default Counter Variable in For loop?

What do you mean by "default"? Why do you need a counter variable? — Karl Knechtel, Dec 28 '10 at 17:33
It's pretty unclear what you're asking, you should type more than a single sentence to a question. — Falmarri, Dec 28 '10 at 22:35

NPE · Accepted Answer · 2010-12-28T22:22:44.067

15

No, you give it a name: for i in range(10): ...

If you want to iterate over elements of a collection in such a way that you get both the element and its index, the Pythonic way to do it is for i,v in enumerate(l): print i,v (where l is a list or any other object implementing the sequence protocol.)

edited Dec 28 '10 at 22:22

answered Dec 28 '10 at 15:51

NPE

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Minor nit - `l` can be anything that implements the sequence protocol, not just a list. – Nick Bastin Dec 28 '10 at 16:29

Kathy Van Stone · Answer 2 · 2010-12-28T17:09:51.200

6

Generally, if you are looping through a list (or any iterator) and want the index as well, you use enumerate:

for i, val in enumerate(l):
   <do something>

edited Dec 28 '10 at 17:09

answered Dec 28 '10 at 15:54

Kathy Van Stone

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There ain't not `enumerate` in your example. – Dec 28 '10 at 15:55
I added the call to enumerate. – Bryan Oakley Dec 28 '10 at 15:59
No enumerate. it should be enumerate(l) – Siva Arunachalam Dec 28 '10 at 16:00

score 5 · Answer 3 · answered Dec 28 '10 at 19:18

5

Simple question, simple answer :

for (i, value) in enumerate(alist):
    print i, value

output :

1 value
2 value
3 value
...

where "value" is the current value of alist (a list or something else).

answered Dec 28 '10 at 19:18

Sandro Munda

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i is zero-indexed, not 1-indexed. To have the output start at 1 use the 'start' keyword argument. – Adam Nelson Apr 15 '11 at 20:35

Python - Default Counter Variable in For loop

3 Answers3