tail

[Dan Stromberg]

I believe I'd do something like:

#!/usr/local/cpython-3.10/bin/python3

"""
Output the last 10 lines of a potentially-huge file.


O(n).  But technically so is scanning backward from the EOF.



It'd be faster to use a dict, but this has the advantage of working for
huge num_lines.
"""



import dbm

import os

import sys





tempfile = f'/tmp/{os.path.basename(sys.argv[0])}.{os.getpid()}'



db = dbm.open(tempfile, 'n')



num_lines = 10



for cur_lineno, line in enumerate(sys.stdin):

    db[str(cur_lineno)] = line.encode('utf-8')

    max_lineno = cur_lineno

    str_age_out_lineno = str(cur_lineno - num_lines - 1)

    if str_age_out_lineno in db:

        del db[str_age_out_lineno]



for lineno in range(max_lineno, max_lineno - num_lines, -1):

    str_lineno = str(lineno)

    if str_lineno not in db:

        break

    print(db[str(lineno)].decode('utf-8'), end='')



db.close()

os.unlink(tempfile)


On Sat, Apr 23, 2022 at 11:36 AM Marco Sulla <Marco.Sulla.Python at gmail.com>
wrote:

> What about introducing a method for text streams that reads the lines
> from the bottom? Java has also a ReversedLinesFileReader with Apache
> Commons IO.
> --
> https://mail.python.org/mailman/listinfo/python-list
>