Extracting embedded Microsoft Office files from an Excel spreadsheet

#!/usr/bin/python

# Name: extract_embedded.py
# Version: 0.1
# Created: 2018-02-14
# Last modified: 2018-02-14
# Description: Accepts the name of an Excel spreadsheet file, such as a
# .xlsx or .xlsm file, that are Office Open XML (OOXML) files as a command
# line argument or, if one is not provided on the command line, will prompt
# for the input fil ename. OOXML is a zipped, XML-based file format developed 
# by Microsoft for representing spreadsheets, charts, presentations and word 
# processing documents. 
#
# The contents of the xl/embeddings subdirectory within the OOXML file will
# be exracted to a directory named "embedded" beneath the current working
# directory. That directory will be created, if it doesn't already exist.
# After the files are extracted, any .bin files that are PowerPoint files
# will be renamed to have a .ppt extension. The olefile module is used to
# determine if a .bin file is a PowerPoint file.

import os, sys

def extractdir(infile):

# Extract all of the embedded files from an Excel .xlsx or .xlsm workbook

   import zipfile

   dirToExtract = "xl/embeddings/"
   destinationDir = "embedded"
   
   if not os.path.exists(destinationDir):
       os.makedirs(destinationDir)
   
   with zipfile.ZipFile(infile) as zip:
       for zip_info in zip.infolist():
           if zip_info.filename.startswith(dirToExtract):
               zip_info.filename = os.path.basename(zip_info.filename)
               zip.extract(zip_info, destinationDir)

def fixExtension(infile):

# If infile is a PowerPoint file with a .bin extension, it will be renamed to
# have a .ppt filename extension.

   import olefile

   # Determine if the first bytes of the file contain the magic number for OLE 
   # files, before opening it. isOleFile returns True if it is an OLE file, 
   # False otherwise 
   if olefile.isOleFile(infile):
      ole = olefile.OleFileIO(infile)
      if ole.exists('PowerPoint Document'):
         path_and_filename, file_extension = os.path.splitext(infile)
         # Replace the .bin extension with a .ppt one
         os.rename(infile, path_and_filename + ".ppt")

# The directory where the embedded files will be stored
path = "embedded"

# Check to see if the file name was entered on the command line.
# If it wasn't prompt for the file name
try:
   sys.argv[1]
except IndexError:
   infile = raw_input("Zip file: ")
else:
   infile = sys.argv[1]

# Extract all embedded files to an "embedded" directory beneath the current
# working directory.
extractdir(infile)
# For all files in the "embedded" directory, if the file is a PowerPoint file
# with a .bin extension, rename the file to have a .ppt extension
for file in os.listdir(path):
    current_file = os.path.join(path, file)
    fixExtension(current_file)