Python note: a file merger

Problem: I've got two folders, containing images from two Cannon camera. They were taken the same day. Unfortunately, these two cameras gave the same names to their pictures. I wanted to merge these two folders, with more powerful functionalities.

Script: This script takes in two folders, moving files from one folder to the other one. When there are duplicate file names, it compares the files. If the files are really duplicated, it only keeps one copy. If the files are different in content, they are renamed to different names by adding postfixes.

Code: The following python source
#
# merge files - merge two folders with no duplicate files
#
g_sWelcome = """
merge_files - merge files from two directories into one.

The files from the "from" directory will be moved to the "to" directory, while
duplicated files will be removed. If two files are in the same name but are
different in signature (revision time, size), the new one will be renamed.

Author: Yue Zhang, 2006
"""
import sys,os
import filecmp
import shutil
#
# Given a path, filename and extention, return a full path name without collision
#
def fileid_alloc(sPath, sPathFrom, sFileName, sExtension):
...global nDuplicateName, nDuplicateContent
...nIndex = 0
...sNewFileName = os.path.join(sPath, sFileName + sExtension)
...if os.path.exists(sNewFileName):
......nDuplicateName += 1
......if filecmp.cmp(sNewFileName, os.path.join(sPathFrom, sFileName + sExtension)):
.........nDuplicateContent += 1
.........return sNewFileName
...while os.path.exists(sNewFileName):
......nIndex += 1
......sNewFileName = os.path.join(sPath, sFileName + str(nIndex) + sExtension)
...return sNewFileName
#
# Main function
#
def merge_files(folder_from, folder_to):
...for sFullFileName in os.listdir(folder_from):
......sFileName, sExtension = os.path.splitext(sFullFileName)
......sNewFileName = fileid_alloc(folder_to, folder_from, sFileName, sExtension)
......shutil.move(os.path.join(folder_from, sFullFileName), sNewFileName)
#
# Main entry
#
if __name__ == '__main__':
...global nDuplicateName, nDuplicateContent
...nDuplicateName = 0
...nDuplicateContent = 0
...print g_sWelcome
...if len(sys.argv) != 3:
......print "Usage: merge_files.py folder_from folder_to"
......sys.exit(0)
...merge_files(sys.argv[1], sys.argv[2])
...print "In all %d duplicate file names processed, among which %d
............duplicate contents are merged and the rest are allocated new name."
............% (nDuplicateName, nDuplicateContent)

Disclaimer: I give no warranty of responsibilities of use of the code, though I have tested this code with my own photos.