Count occurrences of letters in string.

compress.py

"""
hhhhh     aaaaa => h5 5a5
"""

def compress_sentence(sentence):
    prev_letter = sentence[0]
    frequency = 1
    output = ''

    for letter in sentence[1:]:
        if prev_letter == letter:
            frequency += 1
        else:
            output += '%s%s' % (prev_letter, frequency)
            frequency = 1
            prev_letter = letter

    output += '%s%s' % (letter, frequency)

    if len(output) < len(sentence):
        return output

    return sentence


sentence = raw_input("")
print compress_sentence(sentence)