How do I use 2 variables in a Python for loop in the recommended Pythonic way?

Question

I have the following for loop in C that I want to mimic in Python:

for (index = 0; index < n; ++index)
{
    for (i = 0, j = index; j < n; ++i, ++j)
    {
         'do something'
    }
}

Is there a more elegant/Pythonic way to do this, or do I have to declare a variable outside of the loop like so:

for index in range(m):
    i = 0
    for j in range(index, m):
        'do something'
        i += 1

It really depends on what you're doing in that loop. For instance, the loop you describe could be outright replaced by a list comprehension instead. — Makoto
– Makoto, Commented Jan 4, 2016 at 21:12
Probably, but it depends what you're doing in your loop. You rarely want to iterate on a range if you mean to use the value as an index. — Vincent Savard
– Vincent Savard, Commented Jan 4, 2016 at 21:12
index is just going be used as the bounds of my loop and i and j are going to be the indices to a nested list that I want to populate. — Addie
– Addie, Commented Jan 4, 2016 at 21:15
What does the nested list that you want to populate look like? Could you add this information to your question? — Makoto
– Makoto, Commented Jan 4, 2016 at 21:17

Chad S. · Accepted Answer · 2016-01-04 21:15:05Z

1

It's hard to say without knowing more about what is going in the second loop, but as it's written I would say:

for index in range(n):
    for i,j in enumerate(range(index,n)):
        'do something'

would be the way you'd do that.

answered Jan 4, 2016 at 21:15

Chad S.

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2 Comments

That appears to be what I was looking for. I didn't realize you can call enumerate() on a range to populate i and j. Thank you.

You can call enumerate on any iterable.