How to read a file in reverse order?

A correct, efficient answer written as a generator.

import osdef reverse_readline(filename, buf_size=8192):    """A generator that returns the lines of a file in reverse order"""    with open(filename) as fh:        segment = None        offset = 0        fh.seek(0, os.SEEK_END)        file_size = remaining_size = fh.tell()        while remaining_size > 0:            offset = min(file_size, offset + buf_size)            fh.seek(file_size - offset)            buffer = fh.read(min(remaining_size, buf_size))            remaining_size -= buf_size            lines = buffer.split('\n')            # The first line of the buffer is probably not a complete line so            # we'll save it and append it to the last line of the next buffer            # we read            if segment is not None:                # If the previous chunk starts right from the beginning of line                # do not concat the segment to the last line of new chunk.                # Instead, yield the segment first                 if buffer[-1] != '\n':                    lines[-1] += segment                else:                    yield segment            segment = lines[0]            for index in range(len(lines) - 1, 0, -1):                if lines[index]:                    yield lines[index]        # Don't yield None if the file was empty        if segment is not None:            yield segment

for line in reversed(open("filename").readlines()):    print line.rstrip()

And in Python 3:

for line in reversed(list(open("filename"))):    print(line.rstrip())

You can also use python module file_read_backwards.

After installing it, via pip install file_read_backwards (v1.2.1), you can read the entire file backwards (line-wise) in a memory efficient manner via:

#!/usr/bin/env python2.7from file_read_backwards import FileReadBackwardswith FileReadBackwards("/path/to/file", encoding="utf-8") as frb:    for l in frb:         print l

It supports "utf-8","latin-1", and "ascii" encodings.

Support is also available for python3. Further documentation can be found at http://file-read-backwards.readthedocs.io/en/latest/readme.html