wriitng optparse help

gistfile1.txt

#!/usr/bin/python

#
# 
#
# This script watches a TeX file for changes and then runs the
# latex compiler rubber is the file has changed. It then pop open
# the mac pdf viewer Preview.
#
#


#import pickle
import time
import hashlib
import subprocess
import sys
import os
from optparse import OptionParser


def main():
	try:
		l = []
		db = dict(l)
		

		parser = OptionParser(usage="%prog -t TEXFILE -p PDFFILE",version = "%prog 0.1")

		parser.add_option("-t", "--tex-file", dest="texfile",
											help="the TeX file to watch", metavar="TEXFILE")
		parser.add_option("-p","--pdf-file",dest="pdffile",
											help="the PDF file to display", metavar="PDFFILE")
		(options, args) = parser.parse_args()

		if not options.texfile:
			parser.print_help()
			parser.error("You must spcify a TeX file with -t or --tex-file")
		if not options.pdffile:
			parser.print_help()
			parser.error("You must specify a PDF file with -p or --pdf-file")
		if not os.path.exists(options.texfile):
			parser.print_help()
			parse.error("The file: " + options.texfile + "does not exist.")
			
		
		# run rubber and wait for the results
		subprocess.Popen([r"rubber", "--pdf", options.texfile]).wait()
		# open the first time with the filename
		subprocess.Popen([r"open","-a","Preview", options.pdffile])

		# We have to check this after we try running rubber for the first time
		# in case someone has cleaned their PDF file.
		if not os.path.exists(options.pdffile):
			parser.print_help()
			parse.error("The file: " + options.pdffile + "does not exist.")

		# set the access times to be the same since we don't have to go through 
		# the loop before imdiately since we have just run rubber above.
		last_access_time = 0
		latest_access_time = 0
		path = options.texfile

		while True:
			latest_access_time = os.path.getatime(path);
			
			#if the file has been recently accessed 
			if latest_access_time > last_access_time:

				checksum = hashlib.md5(open(path).read()).hexdigest()
				# now check if the hash has changed. Maybe the file was touched or
				# restored from backup but not actually different.
				if db.get(path, None) != checksum:
					print checksum
					print "file changed running rubber"
					subprocess.Popen([r"rubber", "--pdf", options.texfile]).wait()

					# do the preview without the filename. This way preview opens
					# to the right page.
					subprocess.Popen([r"open","-a","Preview"])
					db[path] = checksum
				last_access_time = latest_access_time
			time.sleep(2)
	#catch the control-c keyboard interupt.
 	except (KeyboardInterrupt):
		print options.texfile + " no longer watched"
		sys.exit()
	except (SystemExit):
		sys.exit()
	
main()
#pickle.dump(db.items(), open("db", "w"))