add file with next number

new_invoice.py

import os, sys, re

def die(s):
	print s
	sys.exit ( 1 )

invoice_name = "invoice_"
	
got_files = []
cwd = os.getcwd()	
for root, dirs, files in os.walk(cwd):
    for name in files:
		m = re.match("invoice_(\d*).*", name)
		if m and len(m.group(1)):
			n = os.path.splitext(name)[0] 
			got_files.append((name, int(m.group(1))))

if len(got_files)==0:
	last_file = ('empty', 0)
else:
	last_file = max(got_files, key=lambda x: x[1])
	
print("last file: %s" % last_file[0])
name = "%s%s.txt" % (invoice_name, last_file[1]+1)
print("file: %s" % (name))
fp = open(name, "w")
fp.write("Hi ,\n")
fp.close()