Question

Is it possible to have something like:

list1 = ...  currentValue = 0 list2 = [currentValue += i, i for i in list1] 

I tried that but didn’t work? What’s the proper syntax to write those?

EDIT: the print statement was an example. Actually I am incrementing a value outside the loop.

Answer 1

Statements cannot go inside of expressions in Python; it was a complication that was deliberately designed out of the language. For this problem, try using a complication that did make it into the language: generators. Watch:

def total_and_item(sequence):     total = 0     for i in sequence:         total += i         yield (total, i)  list2 = list(total_and_item(list1)) 

The generator keeps a running tally of the items seen so far, and prefixes it to each item, just like it looks like you example tries to do. Of course, a straightforward loop might be even simpler, that creates an empty list at the top and just calls append() a lot! 🙂