Combining multiple files of uncommon filetype into one

Question

I've created a utility program for combining multiple .vec files into one. The program's main application is in training haar cascade classifiers in openCV (details). This is my first open source contribution that other people may find useful and I would like to improve it if possible.

I'm mainly interested in feedback on the coding style, but any comments would be appreciated.

""" 
 To use the function:
 (1) Place all .vec files to be merged in a single directory (vec_directory).
 (2) Go to the bottom of this file and enter the vec_directory along with an output filename.
 (3) Navigate to this file in your CLI (terminal or cmd) and type "python mergevec.py".
 To test the output of the function:
 (1) Install openCV.
 (2) Navigate to the output file in your CLI (terminal or cmd).
 (2) Type "opencv_createsample -w img_width -h img_height -vec output_filename". 
 This should show the .vec files in sequence.
"""
import sys
import glob
import struct
import traceback
def exception_response(e):
 exc_type, exc_value, exc_traceback = sys.exc_info()
 lines = traceback.format_exception(exc_type, exc_value, exc_traceback)
 for line in lines:
 print(line)
def merge_vec_files(vec_directory, output_vec_file):
 """
 Iterates throught the .vec files in a directory and combines them. 
 (1) Iterates through files getting a count of the total images in the .vec files
 (2) checks that the image sizes in all files are the same
 The format of a .vec file is:
 4 bytes denoting number of total images (int)
 4 bytes denoting size of images (int)
 2 bytes denoting min value (short)
 2 bytes denoting max value (short)
 ex: 6400 0000 4605 0000 0000 0000
 hex 6400 0000 4605 0000 0000 0000
 # images size of h * w min max
 dec 100 1350 0 0
 :type vec_directory: string
 :param vec_directory: Name of the directory containing .vec files to be combined. 
 Do not end with slash. Ex: '/Users/username/Documents/vec_files'
 :type output_vec_file: string
 :param output_vec_file: Name of aggregate .vec file for output. 
 Ex: '/Users/username/Documents/aggregate_vec_file.vec'
 """
 # Check that the .vec directory does not end in '/' and if it does, remove it.
 if vec_directory.endswith('/'):
 vec_directory = vec_directory[:-1]
 # Get .vec files
 files = glob.glob('{0}/*.vec'.format(vec_directory))
 # Check to make sure there are .vec files in the directory
 if len(files) <= 0:
 print('Vec files to be mereged could not be found from directory: {0}'.format(vec_directory))
 sys.exit(1)
 # Check to make sure there are more than one .vec files
 if len(files) == 1:
 print('Only 1 vec file was found in directory: {0}. Cannot merge a single file.'.format(vec_directory))
 sys.exit(1)
 # Get the value for the first image size
 prev_image_size = 0
 try:
 with open(files[0], 'rb') as vecfile:
 content = ''.join(vecfile.readlines())
 val = struct.unpack('<iihh', content[:12])
 prev_image_size = val[1]
 except IOError as e:
 print('An IO error occured while processing the file: {0}'.format(f))
 exception_response(e)
 # Get the total number of images
 total_num_images = 0
 for f in files:
 try:
 with open(f, 'rb') as vecfile: 
 content = ''.join(vecfile.readlines())
 val = struct.unpack('<iihh', content[:12])
 num_images = val[0]
 image_size = val[1]
 if image_size != prev_image_size:
 print('The image sizes in the .vec files differ. These values must be the same.')
 print('The image size of file {0}: {1}'.format(f, image_size))
 print('The image size of previous files: {0}'.format(prev_image_size))
 sys.exit(1)
 total_num_images += num_images
 except IOError as e:
 print('An IO error occured while processing the file: {0}'.format(f))
 exception_response(e)
 # Iterate through the .vec files, writing their data (not the header) to the output file
 # '<iihh' means 'little endian, int, int, short, short'
 header = struct.pack('<iihh', total_num_images, image_size, 0, 0)
 try:
 with open(output_vec_file, 'wb') as outputfile:
 outputfile.write(header)
 for f in files:
 with open(f, 'rb') as vecfile:
 content = ''.join(vecfile.readlines())
 data = content[12:]
 outputfile.write(data)
 except Exception as e:
 exception_response(e)
if __name__ == '__main__':
 # fill in the directory name and the output filename below
 vec_directory = # ex: '/Users/user_name/vec'
 output_filename = # ex: '/Users/user_name/aggregate_vec.vec'
 merge_vec_files(vec_directory, output_filename)

Answer 1

I'm not an expert in Python, but I think you can improve it in some ways:

• Instead of making the user write down the names at the end of the file, you could make the script take them from the console using (after checking they exist)

  vec_directory = sys.argv[1]
  output_filename = sys.argv[2]
  

• Maybe instead of using prints and then exiting with a 1, you can use

  system.exit("Error message")