Character Distribution (Level II)

The purpose of this challenge is to gain proficiency with looping, decision making and lists.

Write and submit a Python program distribution.py that computes and displays the distribution of characters in a given sample of text.

Output of your program should look like this:

Please enter a string of text (the bigger the better): The rain in Spain stays mainly in the plain.
The distribution of characters in "The rain in Spain stays mainly in the plain." is:
iiiiii
nnnnnn
aaaaa
sss
ttt
ee
hh
ll
pp
yy
m
r

Notice about this example:

• The text: The rain ... plain is provided by the user as input to your program.
• Uppercase characters are converted to lowercase
• Spaces and punctuation marks are ignored completely.
• Characters that are more common appear first in the list.
• Where the same number of characters occur, the lines are ordered alphabetically. For example, in the printout above, the letters e, h, l, p and y both occur twice in the text and they are listed in the output in alphabetical order.
• Letters that do not occur in the text are not listed in the output at all.

There are a few techniques or tricks that you may find handy when working on this challenge. If you see something here that sounds useful, feel free to learn more about it!

• The code: 'a string has several characters'.count('a') will return 5, which is the number of times the character 'a' appears in the string.
• The code: zip([1,4,2],['a','z','q']) will return an iterator for generating a list of tuples (another type of list) like this: [(1, 'a'), (4, 'z'), (2, 'q')].
• If mylist is a list like [435, 2, 45, 2] then mylist.sort() will change it to: [2, 2, 45, 435].
• If mylist is a list like [435, 2, 45, 2] then mylist.append(99) will change it to: [435, 2, 45, 2, 99].
• If mylist is a list like [435, 2, 45, 2] then mylist[-1] will return 2, the last element in the list.
• You can get the length of a string, or number of elements in a list using the builtin len() function. For example: len([435, 2, 45, 2]) will return 4.
• If you import string then use string.ascii_lowercase to get a string with the letters a-z in it.

If you find that Python's built-in sort does not work well for you, there are techniques for for customizing it. You can also use your own sorting code. I have included here a sample function that you may borrow to sort lists in a custom way:

def compare(a, b):
    """
    compare - generic comparison function for testing two elements.
    """
    return b > a


def bsort(seq, cmp):
    """
    bsort - simple sorting algorithm that uses any comparison function
    seq - a list to be sorted
    cmp - a function for comparing two elements of seq
    """
    sorted = False  # assume the seq is not sorted to start with
    while not sorted:
        sorted = True   # assume it's already sorted correctly
        for index, value in enumerate(seq): # for every element in seq
            if index > 0:                   # past the first..
                if not cmp(seq[index-1], value):  # if this element is out of order
                    sorted = False          # then the list is not sorted yet
                    seq[index-1], seq[index] = seq[index], seq[index-1] # and swap it

    
tosort = [4, 10, 3, -1000, 30]
bsort(tosort, compare)
print(tosort)