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pythonlist-comprehensionvariable-assignment

How would I modify an outside variable within a list comprehension?

Python code:

i: int = 1
table: list = [[i, bit, None, None] for bit in h]

Expected behaviour: i needs to be incremented by 1 per iteration.

Pseudocode:

i: int = 1
table: list = [[i++, bit, None, None] for bit in h]
Solution

  • List comprehensions shouldn't be used for outside side-effects. In this case, use enumerate instead of an outside variable:

    h = '10010010'  # Undefined in OP example.  Just something to enumerate.
table = [[i, bit, None, None ] for i, bit in enumerate(h, start=1)]
for row in table:
    print(row)

    Output:

    [1, '1', None, None]
[2, '0', None, None]
[3, '0', None, None]
[4, '1', None, None]
[5, '0', None, None]
[6, '0', None, None]
[7, '1', None, None]
[8, '0', None, None]