NoLash gcode backlash compensator (standalone version)

# NoLash ported from java (https://github.com/Lenbok/NoLash) by yclee126
# Standalone version


class NoLash:
    class Axis:
        def __init__(self, name, lash):
            self.name = name
            self.lash = lash
            self.dir = 1
            self.pos = 0

        def reset(self):
            self.dir = 1
            self.pos = 0

    def __init__(self, x, y):
        # forward and backward, thus divided by 2
        self.x_lash = x/2
        self.y_lash = y/2

    def compensate(self, in_file, out_file):
        x = NoLash.Axis('X', self.x_lash)
        y = NoLash.Axis('Y', self.y_lash)

        for line in in_file:
            line = line.strip()

            # get gcode command
            command = line.split(' ', 1)[0]

            # update commands if needed
            if command == 'G0' or command == 'G1':
                line = self.repair_command(x, y, line, out_file)
            elif command == 'G28':
                x.reset()
                y.reset()

            # write (modified) gcode
            out_file.write(line + '\n')

    def repair_command(self, x, y, line, out_file):
        self.countermeasure = ''

        # recalc each axis
        line = self.repair_axis(x, line)
        line = self.repair_axis(y, line)

        # write counterpeasure to file before writing modded line
        if self.countermeasure != '':
            out_file.write(self.countermeasure + '\n')

        return line

    def repair_axis(self, axis, line):
        # check if backlash is present
        if axis.lash <= 0:
            return line

        # remove comments (possibly containing X or Y characters inside)
        line_comments = ''
        parts = line.split(';', 1)
        if len(parts) > 1:
            line, line_comments = parts
            line_comments = ';' + line_comments

        # check if this axis move
        parts = line.split(axis.name, 1)
        if len(parts) == 1:
            return line + line_comments

        # parse value
        line_front, axis_value = parts
        parts = axis_value.split(' ', 1)
        line_back = ''
        if len(parts) > 1:
            axis_value, line_back = parts
            line_back = ' ' + line_back

        new_pos = float(axis_value)

        # compare to curr pos, generate necessary countermeasure
        if not self.is_same_direction(axis, new_pos):
            axis.dir = -axis.dir
            calc = axis.pos + axis.lash * axis.dir # countermeasure pos

            # init countermeasure string
            if self.countermeasure == '':
                self.countermeasure = 'G0'
            self.countermeasure += ' ' + axis.name + str(calc)
        axis.pos = new_pos

        # compensated value
        recalc = new_pos + axis.lash * axis.dir

        # return updated command
        return line_front + axis.name + str(recalc) + line_back

    def is_same_direction(self, axis, new_pos):
        new_dir = 0
        if axis.pos < new_pos:
            new_dir = 1
        elif axis.pos > new_pos:
            new_dir = -1
        else:
            return True
        return new_dir == axis.dir


if __name__ == '__main__':
    # basic CUI interface
    import sys

    # check arg count
    if len(sys.argv) != 5:
        print('Usage: NoLash.py X_LASH Y_LASH IN_FILE.gcode OUT_FILE.gcode')
        exit()

    # parse args
    __name = sys.argv[0]
    x_lash = float(sys.argv[1])
    y_lash = float(sys.argv[2])
    in_file = open(sys.argv[3], 'r', encoding='utf-8')
    out_file = open(sys.argv[4], 'w', encoding='utf-8')

    # process gcode
    no_lash = NoLash(x_lash, y_lash)
    no_lash.compensate(in_file, out_file)

    # close files
    in_file.close()
    out_file.close()