Alter Original Prusa i3 MMU tool changes to stop internal stringing

reram.py

#!/usr/bin/env python

"""Alter Original Prusa i3 MMU tool changes to stop internal stringing.

This changes the filament unload procedure so that right after pulling out,
the extruder pauses (for a little cooling), pushes back in
(to compress the string), and pulls out again (to break the string.)

See: https://github.com/prusa3d/Slic3r/issues/396
"""

import logging
import os.path
import re
import sys

log = logging.getLogger('reram')

unload_comment_re = re.compile(r'; CP TOOLCHANGE UNLOAD')
pull_re = re.compile(r'^G1 E-15\.0000(\s+F\d{4,})?$')


def main():
    logging.basicConfig(level=logging.INFO, file=sys.stderr)

    if len(sys.argv) >= 2:
        # Read from the filename specified in the first arg.
        infn = sys.argv[1]
        infile = open(infn, 'rt')
        outfn = infn + '.tmp'
        outfile = open(outfn, 'wt')
    else:
        # Read from stdin and write to stdout.
        infile = sys.stdin
        infn = None
        outfile = sys.stdout
        outfn = None

    unload_line_no = None
    line_no = 0
    change_count = 0

    write = outfile.write

    for line in infile:
        line_no += 1

        if unload_comment_re.match(line):
            unload_line_no = line_no

        match = pull_re.match(line)
        if match is not None and unload_line_no is not None:
            speed_arg = match.group(1) or ''
            # Pull out.
            write('G1 E-12.0000%s\n' % speed_arg)
            # Pause for a short time for cooling.
            write('G4 P400\n')
            # Ram back in to compress the string.
            write('G1 E12.0000%s\n' % speed_arg)
            # Pull out again, hopefully breaking the string.
            write('G1 E-15.0000%s\n' % speed_arg)
            change_count += 1
            # Don't match again until we see the toolchange unload comment.
            unload_line_no = None

        else:
            write(line)

    infile.close()
    outfile.close()

    # Edit the file in place so this script can be used as a Slic3r
    # post-processing script. See:
    # http://manual.slic3r.org/advanced/post-processing
    if infn and outfn:
        os.rename(outfn, infn)

    log.info('%s changes made', change_count)


if __name__ == '__main__':
    main()

reram.sh

#!/bin/sh
unset PYTHONHOME
unset PYTHONPATH
exec /usr/bin/python "$(dirname $0)/reram.py" "$1"

The script can now be used as a Slic3r post-processing script. I also added the reram.sh wrapper; it's required on Linux because the Prusa Slic3r appimage creates a broken environment for running Python code.