Simple script to act as a sed with python regex

pysed

#! /usr/bin/env python
# credit for the function to https://stackoverflow.com/a/40843600
# Commandline-ification by Robin A. Dorstijn

import re
import shutil
from tempfile import mkstemp
import click

@click.command()
@click.argument("pattern")
@click.argument("replace")
@click.argument("source", type=click.Path(exists=True))
@click.option("--dest", type=click.Path(exists=True))
@click.option("--count", type=click.INT, default=0)
def sed(pattern, replace, source, dest=None, count=0):
    """Reads a source file and writes the destination file.

    In each line, replaces pattern with replace.

    Args:
        pattern (str): pattern to match (can be re.pattern)
        replace (str): replacement str
        source  (str): input filename
        count (int): number of occurrences to replace
        dest (str):   destination filename, if not given, source will be over written.
    """

    fin = open(source, 'r')
    num_replaced = count

    if dest:
        fout = open(dest, 'w')
    else:
        fd, name = mkstemp()
        fout = open(name, 'w')

    for line in fin:
        out = re.sub(pattern, replace, line)
        fout.write(out)

        if out != line:
            num_replaced += 1
        if count and num_replaced > count:
            break
    try:
        fout.writelines(fin.readlines())
    except Exception as E:
        raise E

    fin.close()
    fout.close()

    if not dest:
        shutil.move(name, source)

if __name__=="__main__":
    sed()