Python function that updates first two characters (should be string integers) of each filename in a directory, starting at a given number.

update_increment.py

import os

def update_increment(start_number, directory=None, direction='increment'):

	if directory is None:
		directory = os.path.abspath('.')

	for file_name in os.listdir(directory):

		# The two characters of the filename are numbers
		file_number = int(file_name[0:2])

		if file_number >= start_number:
			if direction is 'decrement':
				file_number -= 1
			else:
				file_number += 1

			# Pad single-digit numbers with a 0 using string formatting
			new_file_name = '%s\%02d%s' % (directory, file_number, file_name[2:])
			old_file_name = '%s\%s' % (directory, file_name)

			#print(old_file_name + "\n  changed to: \n" + new_file_name + "\n")
			os.rename(old_file_name, new_file_name)


#PATH = os.path.abspath('data')

# Increment all files starting at number 10
#update_increment(10, PATH)

# Decrement all files starting at number 10
#update_increment(10, PATH, 'decrement')