The parent poster was pointing out that this requires having two in-memory complete copies of the file:

    [... for row in open(filename).readlines()]

The readlines return value is one copy, and the list comprehension is another copy. However, that first copy can be avoided with:

    [... for row in open(filename)]

The entire file must still be read to evaluate the list comprehension.

Additionally, this doesn't do what you think it does:

    >>> header, *records = (row.strip().split(',') for row in f)

Compare to this, using a variable for clarity:

    >>> gen = (row.strip().split(',') for row in f)
    >>> header, *records = next(gen)