"with" keyword in list comprehension?

Question

I came across this syntax for reading the lines in a file.

with open(...) as f:
    for line in f:
        <do something with line>

Say I wanted the <do something with line> line to append each line to a list. Is there any way to accomplish this, using the with keyword, in a list comprehension? Or, is there at least some way of doing what I want in a single statement?

you could do `[something(line) for line in open("foo.txt")]` but that wouldn't be using `with` — Jean-François Fabre, Apr 25 '17 at 19:19
oneline: `with open("foo.txt") as f: result = [something(line) for line in open("foo.txt")]` — Jean-François Fabre, Apr 25 '17 at 19:21
Just make sure you understand exactly [why `with` is used](http://stackoverflow.com/questions/1369526/what-is-the-python-keyword-with-used-for). — blacksite, Apr 25 '17 at 19:21

fafl · Answer 1 · 2020-03-15T09:13:10.217

You can write something like

with open(...) as f:
    l = [int(line) for line in f]

but you can't put the with into the list comprehension.

It might be possible to write something like

l = [int(line) for line in open(...).read().split("\n")]

but you would need to call f.close() later manually and this way gives you no variable f. It might happen that the filhandle is closed automatically when going out of scope, but I would not rely on it.

score 1 · Answer 2 · answered Apr 25 '17 at 19:21

1

with uses a function as a context manager, so no. f has no value until inside the block. The best you could do is a 2 line implementation.

answered Apr 25 '17 at 19:21

Casey Kinsey

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nope 1 line implementation works. But not one statement, I agree. – Jean-François Fabre Apr 25 '17 at 19:21
Fair enough--you're correct that I was referring to statements rather than lines. – Casey Kinsey Apr 25 '17 at 19:43

"with" keyword in list comprehension?

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