File input frequency sorting - python-3.x

Question

so I have to write a program that:
Takes the filename as an argument.
Reads the file and counts, for each band, how many albums of that band are listed in the file. (http://vlm1.uta.edu/~cconly/teaching/cse1310_spring2015/assignments/assignment7/albums.txt)
Prints on the screen, in descending order of number of albums, a line for each band. Each line should contain the name of the band, followed by a colon and space, and then the number of albums for that band. This would look like this:
band1: number1
band2: number2
band3: number3
so there is my code below, but I keep getting tremendous errors that tells me that things aren't defined when they are, and I'll get this one as well --> TypeError: 'NoneType' object is not iterable, any help would be great!
import fileinput
import os
filename = open("albums.txt", "r") # open album.txt file
def process_line(line):
line = line.lower()
new_line = ""
for letter in line:
if letter in (""",.!"'()"""):
continue
elif letter == '-':
letter = ' '
new_line = new_line + letter
words = new_line.split()
return words
def count_words(filename):
if (os.path.isfile(filename) == False):
print("\nError: file " + filename + " does not exist.\n")
return
#in_file = open(filename, "r")
result = {}
for line in filename:
words = process_line(line)
for word in words:
if (word in result):
result[word] += 1
else:
result[word] = 1
def print_word_frequencies(dictionary):
print()
inverse = inverse_dictionary(dictionary)
frequencies = inverse.keys()
frequencies = list(frequencies) # convert frequencies to a list, so that we can sort it.
frequencies.sort() # sorting the list
frequencies.reverse() # reverse the sorting of the list
for frequency in frequencies: # for words with the same frequency, we want them sorted in
list_of_words = inverse[frequency]
list_of_words.sort() # sorting in alphabetical order
for word in list_of_words:
print(word + ":", frequency)
def inverse_dictionary(in_dictionary):
out_dictionary = {}
for key in in_dictionary:
value = in_dictionary[key]
if (value in out_dictionary):
list_of_keys = out_dictionary[value]
list_of_keys.append(key)
else:
out_dictionary[value] = [key]
return out_dictionary
def main():
filename = "albums.txt"
dictionary = count_words(filename)
print_word_frequencies(dictionary)
main()

Answer 1

Since this is an assignment, I will not give you the full code, but just point out some errors.
First, your indentation is all wrong, and indentation is important in Python! This may just have happened when you pasted your code into the question editor, but maybe not. Particularly, make sure your are not mixing tabs and spaces!
Your count_words method does not return anything, thus dictionary is None and you get TypeError: 'NoneType' object is not iterable in inverse_dictionary
When you do for line in filename, you are iterating the characters in the file name, not the lines in the file, as the global variable filename is shadowed by the filename parameter. Open the file in that method using with open(filename) as the_file:
Your process_line method seems odd. It seems like you remove all the special characters, but then how do you plan to separate band name and album name? You seem to just count words, not albums per band. Try line.split(" - ")[0] to get the band.
All that dictionary-inversing is not needed at all. In print_word_frequencies, just sort the items from the dictionary using some custom key function to sort by the count.
With those hints, you should be able to fix your program. (In case you want to know, I got your program down to about ten lines of code.)