tweet checker

import math

# Maximum number of characters in a valid tweet.
MAX_TWEET_LENGTH = 50

# The first character in a hashtag.
HASHTAG_SYMBOL = '#'

# The first character in a mention.
MENTION_SYMBOL = '@'

# Underscore is the only non-alphanumeric character that can be part
# of a word (or username) in a tweet.
UNDERSCORE = '_'

SPACE = ' '


def is_valid_tweet(text: str) -> bool:
    ''' Return True IFF the potential tweet contains between 1 and
    MAX_TWEET_LENGTH characters, inclusive.

    >>> is_valid_tweet('Hello Twitter!')
    True
    >>> is_valid_tweet('')
    False
    >>> is_valid_tweet(2 * 'ABCDEFGHIJKLMNOPQRSTUVWXYZ')
    False
    '''
    return (len(text) <= MAX_TWEET_LENGTH) and (len(text) >= 1)


def compare_tweet_lengths(tweet1: str, tweet2: str) -> int:
    '''Return one of three integers to indicate the difference
    between the length of the two tweets;
    1: if the first tweet is longer than the second.
    -1: if the second tweet is longer than the first.
    0: if the tweets have the same length.
    >>> compare_tweet_lengths('Im very tired right now', 'True')
    1
    >>> compare_tweet_lengths('AbC', 'abcDEF')
    -1
    >>> compare_tweet_lengths('ABC', 'abc')
    0
    '''
    if len(tweet1) > len(tweet2):
        return 1
    if len(tweet1) < len(tweet2):
        return -1
    if len(tweet1) == len(tweet2):
        return 0


def add_hashtag(orig_tweet: str, tweet_word: str) -> str:
    '''Return a potential tweet if the tweet is still valid after appending a
    space, hash symbol, and tweet_word to the end of the orig_tweet.
    Otherwise return the original tweet.
    >>> add_hashtag('I like', 'csc108')
    'I like #csc108'
    >>> add_hashtag('I like', 20 * 'csc108')
    'I like'
    '''
    new_tweet = orig_tweet + SPACE + HASHTAG_SYMBOL + tweet_word
    if len(new_tweet) <= MAX_TWEET_LENGTH:
        return new_tweet
    else:
        return orig_tweet


def helper_function(orig_tweet: str, tweet_word: str, constant: str) -> bool:
    clean_tweet = clean(orig_tweet)
    split_tweet = clean_tweet.split()
    maybe_tweet_word = ''
    for i in split_tweet:
        if i[0] == constant:
            maybe_tweet_word = i
        if len(maybe_tweet_word) == len(constant + tweet_word):
            return True

    return False


def contains_hashtag(orig_tweet: str, tweet_word: str) -> bool:
    '''Return True if tweet_word appears within orig_tweet and
    is appended at the end of a hashtag (made up of the hash symbol).
    >>> contains_hashtag('I like #csc108', 'csc108')
    True
    >>> contains_hashtag('I like #csc108', 'csc')
    False
    >>> contains_hashtag('this hashtag has #An_Underscore', 'An_Underscore')
    True
    >>> contains_hashtag('#The #hash #symbol not missing.', 'symbol')
    True
    >>> contains_hashtag('not #onlypartial #hashtag word @here #only', 'only')
    True
    '''
    a = helper_function(orig_tweet, tweet_word, HASHTAG_SYMBOL)
    return a


def is_mentioned(orig_tweet: str, tweet_word: str) -> bool:
    '''Return True IFF the the orig_tweet contains a mention
    made up of the mention symbol and the exact tweet_word.
    >>> is_mentioned('Go @Raptors', 'Raptors')
    True
    >>> is_mentioned('Go @Raptors', 'Raps')
    False
    >>> is_mentioned('this mention has @An_Underscore', 'An_Underscore')
    True
    >>> is_mentioned('@the @at @symbol is present', 'symbol')
    True
    >>> is_mentioned('not @onlypartial @mention word #here @only', 'only')
    True
    '''
    b = helper_function(orig_tweet, tweet_word, MENTION_SYMBOL)
    return b


def add_mention_exclusive(orig_tweet: str, tweet_word: str) -> str:
    '''Return the potential tweet IFF the orig_tweet doesn't already mention
    the tweetWord and the potential tweet is still valid after a space, mention symbol,
    tweet_word are appended to the end of the orig_tweet.
    Otherwise,return the orig_tweet.
    >>> add_mention_exclusive('Go Raptors!', 'Raptors')
    'Go Raptors! @Raptors'
    >>> add_mention_exclusive('Go @Raptors!', 'Raptors')
    'Go @Raptors!'
    >>> add_mention_exclusive('#does @not? contain, mention; word!', 'foobar')
    '#does @not? contain, mention; word! @foobar'
    >>> add_mention_exclusive('Non_mention w, #contained at @start', 'Non_mention')
    'Non_mention w, #contained at @start @Non_mention'
    '''
    if is_mentioned(orig_tweet, tweet_word):
        return orig_tweet
    else:
        return orig_tweet + SPACE + MENTION_SYMBOL + tweet_word


def num_tweets_required(message: str) -> int:
    '''Return the minimum number of tweets that would be required to communicate the entire message.
    >>> num_tweets_required('First dad joke: My boss told me to have a good day... so i went home.')
    2
    >>> num_tweets_required('I proposed to my ex-wife. But she said no. She believes I’m just after my money.')
    2
    '''
    number_of_tweets = math.ceil(len(message) / MAX_TWEET_LENGTH)
    return number_of_tweets


def get_nth_tweet(message: str, n: int) -> str:
    '''Return the nth valid tweet in the sequence of tweets within a message.
    >>> get_nth_tweet('This message is fifty characters long, this fifty.', 0)
    'This message is fifty characters long, this fifty.'
    >>> get_nth_tweet('This message is fifty characters long. This message is fifty characters long. ', 0)
    'This message is fifty characters long. This messag'
    >>> get_nth_tweet('This message is fifty characters long, this fifty.', 1)
    ''
    >>> get_nth_tweet('This message is fifty characters long. This message is fifty characters long. ', 1)
    'e is fifty characters long. '
    '''
    if n > num_tweets_required(message):
        return ''

    num_tweets_skipped = n
    index = num_tweets_skipped * MAX_TWEET_LENGTH
    return message[index: index + (MAX_TWEET_LENGTH)]


def clean(text: str) -> str:
    '''Return text with every non-alphanumeric character, except for
    HASHTAG_SYMBOL, MENTION_SYMBOL, and UNDERSCORE, replaced with a
    SPACE, and each HASHTAG_SYMBOL replaced with a SPACE followed by
    the HASHTAG_SYMBOL, and each MENTION_SYMBOL replaced with a SPACE
    followed by a MENTION_SYMBOL.

    >>> clean('A! lot,of punctuation?!!')
    'A  lot of punctuation   '
    >>> clean('With#hash#tags? and@mentions?in#twe_et #end')
    'With #hash #tags  and @mentions in #twe_et  #end'
    '''
    clean_str = ''
    for char in text:
        if char.isalnum() or char == UNDERSCORE:
            clean_str = clean_str + char
        elif char == HASHTAG_SYMBOL or char == MENTION_SYMBOL:
            clean_str = clean_str + SPACE + char
        else:
            clean_str = clean_str + SPACE
    return clean_str