remove common words from filenames

#!/usr/bin/python

#import libraries to be used
import sys
import os
import collections
import itertools

#create a list of the files whose names I'd like to change
old_file_names = os.listdir(".")
num_files=len(old_file_names)

#this next threshold value signifies the minimum number of files that a word must appear in to be deleted
repetition_threshold = num_files-4

#start with the list of files, extract the prefix and suffix
#convert different kinds of word breaks such as '_' '-' ',' '.' and convert them all to spaces
#tidy up the file names, removing trailing and extra white spaces
#at the moment no renaming is done.  Simply a list of names has been tidied
file_suffixes=[x[-4:] for x in old_file_names]
new_file_prefixes=[x[:-4] for x in old_file_names]
new_file_prefixes=[x.replace("_"," ") for x in new_file_prefixes]
new_file_prefixes=[x.replace("-"," ") for x in new_file_prefixes]
new_file_prefixes=[x.replace("."," ") for x in new_file_prefixes]
new_file_prefixes=[x.replace("  "," ") for x in new_file_prefixes]
new_file_prefixes=[x.replace("  "," ") for x in new_file_prefixes]
new_file_prefixes=[x.replace("  "," ") for x in new_file_prefixes]
new_file_prefixes=[x.replace("  "," ") for x in new_file_prefixes]
new_file_prefixes=[x.strip() for x in new_file_prefixes]

#Now need to make a list of all the words used in all the files.
#From this we will determine if any words are repeated.  These are the words we will remove.
words_in_file_names = [file_prefix.split() for file_prefix in new_file_prefixes]
#now flatten this list
words_in_file_names = list(itertools.chain.from_iterable(words_in_file_names))
#this next list dict contains all the words which have been repeated a lot.
dict= [x for x, y in collections.Counter(words_in_file_names).items() if y > repetition_threshold]

#if there are common (ie repeated) words, delete them from the list of tidied file names
#if there are no common words, I would still like the tidied names to be applied to the files, so the script continues below
if len(dict)>0:
    for word in dict:
        new_file_prefixes=[x.replace(word,"") for x in new_file_prefixes]

#reconstruct the new file names as prefix + suffix
new_file_names=[new_file_prefixes+file_suffixes for new_file_prefixes,file_suffixes in zip(new_file_prefixes,file_suffixes)]

#finally, perform the renaming
[os.rename(old_file_names[i], new_file_names[i]) for i in range(num_files)]