My function is not returning the expected value

When I run the program, the function percentagefreq returns "none".

What am I doing wrong?

def main():
    file = raw_input("Please enter name of file: ")
    s = readfile(file)
    print
    print "The file contains:"
    print s
    lc = tolowercase(s)
    print "The file in lowercase is:"
    print lc
    print
    compressedTxt = nospaces(lc)
    print "The alphabetic characters alone are:"
    print compressedTxt
    print
    Count = alpha(lc)  
    nonchr = len(s) - Count
    print "The number of alphabetic characters are: ", Count
    print "The number of non-alphabetic charcters are: ", nonchr
    print
    print "Letter\tFrequency\tPercentage"
    countFreq(compressedTxt)
    percent = percentagefreq(Count)
    print percent


def readfile(file):
    text = open(file,"r")
    s = text.read()
    text.close()
    return s

def tolowercase(s):
    lc = ""
    for x in s:
        if "A" <= x <= "Z":
            lc = lc + chr(ord(x) + 32)
        else:
            lc = lc + x
    return lc

def nospaces(lc):
    compressedTxt = ""
    for x in lc:
        if "a" <= x <= "z":
            compressedTxt = compressedTxt + x

    return compressedTxt


def alpha(lc):
    Count = 0
    for x in lc:
    开发者_JAVA百科    if "a" <= x <= "z":
            Count = Count + 1
    return Count


def countFreq(compressedTxt):
    global freq
    freq = ""
    az = ('abcdefghijklmnopqrstuvwxyz')
    for x in az:
        freq = compressedTxt.count(x)
        print x, "\t", freq,"\t"

def percentagefreq(Count):
    for i in range(freq):
        percent = i/Count
        return percent

#I am trying to calculate the percentage of each letter appearing in a file of text

main()

You should check the value of freq. If the value is 0, then the loop will never run and percentagefreq will not return a value.

Looking at the loop,

for x in az:
    freq = compressedTxt.count(x)
    print x, "\t", freq,"\t"

freq will have the last value (count(z)) which is most likely zero.

You're doing pretty much everything wrong, sorry to say. My comments on the other answer explain several of the problems. Here are some other improvements as well:

def main():
    # There is really no reason to pull out a separate function
    # for something as simple as opening and reading a file. It
    # can be done in one line, and the following is a simpler way
    # of handling the file-closing logic:
    filename = raw_input("Please enter name of file: ")
    with open(filename) as f: s = f.read()
    print
    print "The file contains:"
    print s
    # Again, lowercasing is built right in; no reason to write it yourself.
    lc = s.lower()
    print "The file in lowercase is:"
    print lc
    print
    # 'nospaces' is a bad name for your function because you're
    # actually removing everything that's not a letter.
    # Again, there is a trivial one-liner for this:
    compressed = filter(str.isalpha, lc)
    print "The alphabetic characters alone are:"
    print compressed
    print
    # There is a much simpler way to count the alphabetic
    # and non-alphabetic characters: we already have the
    # string of all the alphabetic characters, and strings
    # know how long they are, so:
    Count = len(compressed)
    nonchr = len(s) - Count
    print "The number of alphabetic characters are: ", Count
    print "The number of non-alphabetic charcters are: ", nonchr
    print
    print "Letter\tFrequency\tPercentage"
    # Your logic is entirely messed up here: you can't print all the
    # letters and frequencies, and then magically go back and insert
    # the percentages. You need to calculate the frequencies first, then
    # calculate the percentages from the frequencies, and then you can
    # print everything out.
    # Again, counting the frequencies and actually building a list
    # (as you need) is a one-liner:
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    # By the way, notice how I'm not abbreviating my names?
    frequencies = [compressedTxt.count(letter) for letter in alphabet]
    # that is: stop trying to tell Python how to put together a list of data,
    # and ask it for the data you want. Similarly:
    percentages = [f / float(Count) for f in frequencies]
    # Notice the conversion there: if you just divide through with two integers,
    # you will throw away the remainder (which for your case means you'll get 0
    # for every value).
    # Now we'll output the data, by using the built-in 'zip' function
    # to take pairs of data from the two lists:
    for l, f, p in zip(alphabet, frequencies, percentages):
        print l, '\t', f, '\t', p


main()

Without the comments and diagnostics, we get something as simple as:

def main():
    filename = raw_input("Please enter name of file: ")
    with open(filename) as f: data = filter(str.isalpha, f.read().lower())
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    frequencies = [data.count(letter) for letter in alphabet]
    percentages = [f / float(len(data)) for f in frequencies]
    print "Letter\tFrequency\tPercentage"
    for l, f, p in zip(alphabet, frequencies, percentages):
        print l, '\t', f, '\t', p

Or, even more simply, you could just calculate the values within the loop (the above was mostly to show the techniques necessary to actually pass around data the way you seem to want to):

def main():
    filename = raw_input("Please enter name of file: ")
    with open(filename) as f: data = filter(str.isalpha, f.read().lower())
    print "Letter\tFrequency\tPercentage"
    for letter in 'abcdefghijklmnopqrstuvwxyz':
        frequency = data.count(letter)
        print letter, '\t', frequency, '\t', frequency / float(len(data))