CHARS_TO_REMOVE = '.,"\';:!()?[]'

def normalize_word(word):
    '''Return a word lowercase and stripped of punctuation.

    NOTE: you don't need to use this function or anything
    like it for Lab 9. Use the "re.findall" code specified
    in the lab question instead.'''

    for char in CHARS_TO_REMOVE:
        word = word.replace(char, '')
    return word.lower()
    

def count_words(filename):
    '''returns a dictionary mapping words to the number
    of times the word appears in filename'''
    
    word_counts = {} # maps words (strings) to occurrences (ints)
    
    file = open(filename, errors='ignore')
    
    for line in file:
        line = line.strip() # throw away newline
        
        words = line.split() # get all the words in the line
        
        for word in words:
            word = normalize_word(word)
            
            # add the word to the map or increase its count
            word_counts[word] = word_counts.get(word, 0) + 1
            
    file.close()
    
    return word_counts


def top_words(filename, num_words):
    '''Return a list of the num_words most frequently occurring
    words in filename. Each element of the list should be a
    tuple consisting of (word, frequency).'''
    
    word_map = count_words(filename) # construct the word map
    sorted_keys = sorted(word_map, key=word_map.get)
 #   sorted_keys.reverse()
    
    top_list = []
    for i in range(num_words):
        word = sorted_keys[i]
        word_tuple = (word, word_map[word])
        top_list.append(word_tuple)
    
    return top_list


def unique_words(filename, all_filenames):
    '''Return a set of words that appear in the string filename
    but no other files in the list all_filenames'''
    file_unique_words = set(count_words(filename).keys())
    
    for other_filename in all_filenames:
        if other_filename != filename: # don't compare a file with itself
            other_unique_words = set(count_words(other_filename).keys())
            file_unique_words -= other_unique_words
        
    return file_unique_words


def print_reciprocal(number):
    '''Prints the reciprocal of number'''
    recip = 1.0 / number
    print('Reciprocal of {0} is {1}'.format(number, recip))
    
    
def print_reciprocal2(number):
    '''Prints the reciprocal of number'''
    try:
        # code that might throw an exception
        recip = 1.0 / number
    except:
        # run this block if there IS an exception
        print('{0} does not have a reciprocal'.format(number))
    else:
        # run this block if there is NO exception
        print('Reciprocal of {0} is {1}'.format(number, recip)) 
        
        
def print_reciprocal3(number):
    '''Prints the reciprocal of number'''
    try:
        # code that might throw an exception
        recip = 1.0 / number
    except ZeroDivisionError:
        # run this block if a ZeroDivisionError occurs
        print('Can\'t divide by zero')
    except TypeError:
        # run this block if a TypeError occurs
        print('{0} is not a number'.format(number))
    else:
        # run this block if there is NO exception
        print('Reciprocal of {0} is {1}'.format(number, recip))