List comprehensions splitting loop variable

Question

I am trying to find out if there is a way to split the value of each iteration of a list comprehension only once but use it twice in the output.

As an example of th

Answer 1

You could use a list comprehension wrapped around a generator expression:

[(x[1],x[2]) for x in (x.split(";") for x in a.split("\n")) if x[1] != 5]

Answer 2

Starting Python 3.8, and the introduction of assignment expressions (PEP 572) (:= operator), it's possible to use a local variable within a list comprehension in order to avoid calling twice the same expression:

In our case, we can name the evaluation of line.split(';') as a variable parts while using the result of the expression to filter the list if parts[1] is not equal to 5; and thus re-use parts to produce the mapped value:

# text = '1;2;4\n3;4;5'
[(parts[1], parts[2]) for line in text.split('\n') if (parts := line.split(';'))[1] != 5]
# [('2', '4'), ('4', '5')]