3 ms·
> No need to read the lines all into memory first. It looks like that code does read the whole file: (with a foo.csv that is 350955 bytes long:) % python -
by philsnow 3y ago
> No need to read the lines all into memory first.
It looks like that code does read the whole file:
(with a foo.csv that is 350955 bytes long:)
% python -V
Python 3.11.4
% python
>>> f = open("foo.csv")
>>> f.tell()
0
>>> header, *records = [row.strip().split(',') for row in f]
>>> f.tell()
350955
I thought that using a list comprehension to bind header and records was eagerly consuming the file, so I changed it to a generator comprehension with
>>> f.close()
>>> f.open("foo.csv")
>>> header, *records = (row.strip().split(',') for row in f)
>>> f.tell()
350955
nope, I guess the destructuring bind does it?
>>> f.close()
>>> f.open("foo.csv")
>>> headers, records = f.readline().strip().split(','), (row.strip().split(',') for row in f)
>>> f.tell()
125
not as neat, though. Is there a golf-ier way to do it?*
- me-vs-cat 3y agoThe 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)