focal_length.py

#!/usr/bin/env python
# Author: Justin Lintz
# usage: ./focal_length dir
# Requiresments: dcraw http://www.cybercom.net/~dcoffin/dcraw/
import os
import sys
from subprocess import Popen, PIPE
from operator import itemgetter

DCRAW='dcraw' # or /path/to/dcraw

def count(it):
    d={}
    for x in it:
        d[x]=d.get(x,0)+1

    l = d.items()
    l.sort(key=itemgetter(1),reverse=True)
    return l

def get_focal_length(filename):
    p = Popen([DCRAW,'-i','-v',filename],stdout=PIPE)
    for line in p.stdout:
        if line.startswith('Focal'): 
            length = line.split(':')[1].strip()
            focal = length[:-2]
            return focal

def get_raw_files(path):
    file_list = []
    for root,dirs,files in os.walk(path):
        for filename in files:
            if filename.endswith('CR2'):
                file_list.append(os.path.join(root,filename))
    return file_list

def main(path):
    files = get_raw_files(path)
    print 'Total pics to process: %d' % len(files)
    focal_lengths = (get_focal_length(filename) for filename in files)
    focal_counts = count(focal_lengths)
    for length,num in focal_counts:
        print 'Length: %s , Count: %d' % (length,num) 
    return 0
    
if __name__ == "__main__":
    path = sys.argv[1]
    main(path)