Loops and things

[Tim Chase]

> I was wondering how and if it's possible to write a loop in python
> which updates two or more variables at a time. For instance, something
> like this in C:
> 
> for (i = 0, j = 10; i < 10 && j < 20; i++, j++) {
>     printf("i = %d, j = %d\n", i, j);
> }

Well, yes it can be done, but depending on your use-case, there
might be smarter ways of doing it:

  for (i,j) in map(lambda i: (i, i+10), xrange(10)):
    print "i = %d, j = %d" % (i,j)

or just

  for pair in map(lambda i: (i, i+10), xrange(10)):
    print "i = %d, j = %d" % pair

or even just

  for i in xrange(10):
    print "i = %d, j = %d" % (i,i+10)

If you need varying sources, you can use zip() to do something like

  for (i,j) in zip(xrange(10), myiter(72)):
    print "i = %d, j = %d" % (i,j)

where myiter() produces the random sequence of items for j.

If they produce voluminous output, you can import itertools and
use izip and imap instead.

Or, if you want a more literal mapping:

  i, j = 0, 10
  while i < 10 && j < 20:
    print "i = %d, j = %d" % (i,j)
    i += 1
    j += 1

Pick your poison.

> So that I would get:
> 
> i = 0, j = 0
> i = 1, j = 1
> i = 2, j = 2
> ...
> ...

I'm not sure how, with your code, "j" could be (0,1,2,...)
instead of (10,11,12,...).

-tkc