Change track names in GPX files (python)

GpxTrackNameChanger.py

#!/usr/bin/python

# Script for assigning the date of a track in a GPX file as track name.
#
# Usage e.g $ python ChangeGpxTrackName.py source.gpx target.gpx"
#
# Peter Vasil
# Date: 2011-02-05

from optparse import OptionParser
import sys
import os.path
from lxml import etree

def main():
    usage = "usage: %prog 'inputfile' 'outputfile'"
    parser = OptionParser(usage, version="%prog 0.1")
    (options, args) = parser.parse_args()
    if len(args) != 2:
        parser.error("\nplease enter the input and output GPX files")
    
    infile, outfile = args
    
    if not(os.path.isfile(infile)):
        print "input file does not exist"
        exit(1)
    
    # parser = etree.XMLParser(ns_clean=True)
    tree = etree.parse(infile)
    namespace = "http://www.topografix.com/GPX/1/0"
    trks = tree.findall("{%s}trk" % namespace)
    
    trk_num = 0
    for trk in trks:
        name = trk.find("{%s}name" % namespace)
        time = trk.find(".//{%s}time" % namespace)
        trk_num += 1
        print "-----------------------------------------"
        print "Track number: %d" % trk_num
        print "Old name: %s" % name.text
        print "New name: %s" % time.text
        name.text = time.text
    print "-----------------------------------------"

    treestring = etree.tostring(tree, encoding="utf-8", xml_declaration=True)
    file = open(outfile, 'w')
    file.write(treestring)
    file.close()

if __name__ == '__main__':
    sys.exit(main())