"""
 cipher_functions.py

 Using our earlier crypto example
 as a demonstration of functions and doctests.

 This is my recommended model for simple programming in python.

 Jim M | Oct 2013
"""

def encode_char(character, key):
    """ Given a lowercase character, return it shifted upward by the key.
        >>> encode_char('a', 3)  # three characters after 'a'
        'd'
        >>> encode_char('z', 2)  # wrap around
        'b'
    """
    ascii_value = ord(character)                 # e.g.  97 for 'a'
    zero_to_25 = ascii_value - ord('a')          # e.g.   0 for 'a'
    crypt_0_to_25 = (zero_to_25 + key) % 26      # e.g.   0+3 for key=3
    crypt_ascii = ord('a') + crypt_0_to_25       # e.g. 100
    crypt_char = chr(crypt_ascii)                # e.g. 'd'
    return crypt_char

def encode_word(word, key):
    """ Return the lowercase word shifted upward by the key.
        >>> encode_word("cat", 3)  # c shifts to f, a to d, t to 2
        'fdw'
        >>> encode_word("zoo", 5)
        '?'
    """
    crypt_word = ""
    for char in word:
        crypt_word = crypt_word + encode_char(char, key)
    return crypt_word

def main():
  print "-- cipher ---\n"
  key = int(raw_input("What is the key? (13) "))
  plain_text = raw_input("What is the lowercase word? (cat) ")
  crypt_text = encode_word(plain_text, key)
  print "'{}' encrypted is '{}'".format(plain_text, crypt_text)


if __name__ == "__main__":      # invoked as "python cipher_functions.py" ?
    import doctest
    doctest.testmod()           # Run all the tests. (Do nothing if OK.)
    main()                      # Run the main() program.