Question

I find myself frequently writing code like this:

k = 0
for i in mylist:
    # y[k] = some function of i
    k += 1

Instead, I could do

for k in range(K):
    # y[k] = some function of mylist[k]

but that doesn’t seem “pythonic”. (You know… indexing. Ick!) Is there some syntax that allows me to extract both the index (k) and the element (i) simultaneously using either a loop, list comprehension, or generator? The task is in scientific computing, so there is a lot of stuff in the loop body, making a list comprehension probably not powerful enough on its own, I think.

I welcome tips on related concepts, too, that I might not have even though of. Thank you.

Answer 1

You can use enumerate:

for k,i in enumerate(mylist):
    #do something with index k
    #do something with element i

More information about looping techniques.

Edit:
As pointed out in the comments, using other variable names like

for i, item in enumerate(mylist):

makes it easier to read and understand your code in the long run. Normally you should use i, j, k for numbers and meaningful variable names to describe elements of a list.
I.e. if you have e.g. a list of books and iterate over it, then you should name the variable book.