I'm a beginner to python, but I can't find anything on the internet to help me with this problem:
I want to append different values to 2 different lists at once (the actual problem is more complex than this but I just need to know the right syntax so I'm simplifying it)
test1= []
test2= []
[test1.append(1) and test2.append(2) for i in range (10)]
this doesn't append to both lists, how do I make that happen?
Firstly I don't get why you need it in 1 line, there seems to be no good reason for this, anyway I guess you could do this:
test1, test2 = [], []
for _ in range(10): test1.append(1); test2.append(2)
If your specific example is what you want, use argument unpacking to assign multiple values at once:
test1, test2 = [1] * 10, [2] * 10
You can also use the zip(*x) idiom to transpose a 2-column list:
test1, test2, map(list, zip(*[[1, 2]] * 10))
If you're OK with having tuples instead of lists, you can omit the map(list, ...) wrapper.
The best way I know of having a comprehension with side-effects is using collections.deque with a size of zero, so it runs the iterator but does not store any results:
from collections import deque
test1, test2 = [], []
deque(((test1.append(1), test2.append(2)) for _ in range(10)), maxlen=0)
The generator creates tuples (None, None) every time (since list.append returns None), which the deque promptly discards.