exercise10_3.py

"""
Exercise  10.3: Write a program that reads a file and prints the letters in
decreasing order of frequency. Your program should convert all the input to 
lower case and only count the letters a-z. Your program should not count
spaces, digits, puntuaction, or anything other than letters a-z. Find text
samples from several different languages and see how letter frequency varies
between languages. Compare your results with the tables at 
wikipedia.org/wiki/Letter_frequencies

Python for Everybody: Exploring Data Using Python 3
by Charles R. Severance

Solution by Jamison Lahman, June 1, 2017
"""
import string

counts = 0
dictionary_counts = dict()                       #Initializes the dictionary
fname = input('Enter file name: ')
try:
    fhand = open(fname)
except:
    print('File cannot be opened:', fname)
    exit()
    
for line in fhand:
    line = line.translate(str.maketrans('', '', string.digits))
    line = line.translate(str.maketrans('', '', string.punctuation))
    line = line.lower()
#Removes numbers then punctuation, and lower cases the letters
    words = line.split()
    for word in words:
        for letter in word:
            counts += 1          #counts each letter for relative frequencies
            if letter not in dictionary_counts:
                dictionary_counts[letter] = 1
            else:
                dictionary_counts[letter] += 1
                
relative_lst = list()           #Initializes the list
for key, val in list(dictionary_counts.items()):
    relative_lst.append((val/counts,key))    #Computes the relative frequency
    
relative_lst.sort(reverse=True)             #Sorts from highest rel freq

for key, val in relative_lst:                
    print(key,val)