#!/usr/bin/env python

"""A tiny tool used to test the `convert` plugin. It copies a file and appends
a specified text tag.
"""

import sys


def convert(in_file, out_file, tag):
    """Copy `in_file` to `out_file` and append the string `tag`.
    """
    with open(out_file, 'wb') as out_f:
        with open(in_file, 'rb') as in_f:
            out_f.write(in_f.read())
        out_f.write(tag)


if __name__ == '__main__':
    convert(sys.argv[1], sys.argv[2], sys.argv[3])

#!/usr/bin/env python

"""A tiny tool used to test the `convert` plugin. It copies a file and appends
a specified text tag.
"""

import sys


def convert(in_file, out_file, tag):
    """Copy `in_file` to `out_file` and append the string `tag`.
    """
    # On Python 3, encode the tag argument as bytes.
    if not isinstance(tag, bytes):
        tag = tag.encode('utf8')

    with open(out_file, 'wb') as out_f:
        with open(in_file, 'rb') as in_f:
            out_f.write(in_f.read())
        out_f.write(tag)


if __name__ == '__main__':
    convert(sys.argv[1], sys.argv[2], sys.argv[3])

Convert stub: Python 3 compatibility