Multiple statements in list compherensions in Python?

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 wor

Answer 1

Print is a weird thing to call in a list comprehension. It'd help if you showed us what output you want, not just the code that doesn't work.

Here are two guesses for you. Either way, the important point is that the value statement in a list comprehension has to be a single value. You can't insert multiple items all at once. (If that's what you're trying to do, skip to the 2nd example.)

list1 = [1, 2, 3]
list2 = [(i, i*2, i) for i in list1]
# list2 = [(1, 2, 1), (2, 4, 2), (3, 6, 3)]

To get a flat list:

list1 = [1, 2, 3]
tmp = [(i, i*2) for i in list1]
list2 = []
map(list2.extend, tmp)
# list2 = [1, 2, 1, 2, 4, 2, 3, 6, 3]

Edit: Incrementing a value in the middle of the list comprehension is still weird. If you really need to do it, you're better off just writing a regular for loop, and appending values as you go. In Python, cleverness like that is almost always branded as "unpythonic." Do it if you must, but you will get no end of flak in forums like this. ;)