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[killerrex]

In that form is just to create a list, as the [x for x in xxx] is a syntactic sugar for list(x for x in xxx).
In particular the part of "x for x in xxx" produces a generator, that you can pass it to any place in python that accepts a generator as input (behaves as the command "range")

The other 2 "pretty" syntax similar to that one is to create a set or a dictionary:

# Imagine fd contains 1, 2, 555, 44
# You only want the different numbers, no matter the repetitions => Create set of numbers
>>> {int(s.strip()) for s in fd}
{1, 2, 555, 44}

# You want to create a dictionary initialising the entry to something
>>> {int(s.strip()): 'xxx' for s in fd}
{1: 'xxx', 2: 'xxx', 44: 'xxx', 555: 'xxx'}

# If you want to create a tuple you can do it with:
>>> tuple(int(s.strip()) for s in fd)
(1, 2, 44, 555)