I am writing a code to take an enormous textfile (several GB) N lines at a time, process that batch, and move onto the next N lines until I have completed the entire file. (I don't care if the last batch isn't the perfect size).
I have been reading about using itertools islice for this operation. I think I am halfway there:
from itertools import islice
N = 16
infile = open("my_very_large_text_file", "r")
lines_gen = islice(infile, N)
for lines in lines_gen:
...process my lines...
The trouble is that I would like to process the next batch of 16 lines, but I am missing something
islice()
can be used to get the next n
items of an iterator. Thus, list(islice(f, n))
will return a list of the next n
lines of the file f
. Using this inside a loop will give you the file in chunks of n
lines. At the end of the file, the list might be shorter, and finally the call will return an empty list.
from itertools import islice
with open(...) as f:
while True:
next_n_lines = list(islice(f, n))
if not next_n_lines:
break
# process next_n_lines
An alternative is to use the grouper pattern:
with open(...) as f:
for next_n_lines in izip_longest(*[f] * n):
# process next_n_lines