Python fastest way to read a large text file (several GB)

Question

I have a large text file (~7 GB). I am looking if exist the fastest way to read large text file. I have been reading about using several approach as read chunk-by-chunk in order to speed the process.

at example effbot suggest

# File: readline-example-3.py

file = open("sample.txt")

while 1:

    lines = file.readlines(100000)

    if not lines:

        break

    for line in lines:

        pass # do something**strong text**

in order to process 96,900 lines of text per second. Other authors suggest to use islice()

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

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

Answer 1

Just open the file in a with block to avoid having to close it. Then, iterate over each line in the file object in a for loop and process those lines. e.g.:

with open("file.txt") as f:

    for line in f:

        process_lines(line)

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