# Source code for py_stringmatching.tokenizer.alphabetic_tokenizer

    import re

    from py_stringmatching import utils
    from py_stringmatching.tokenizer.definition_tokenizer import DefinitionTokenizer

    class AlphabeticTokenizer(DefinitionTokenizer):
        """Returns tokens that are maximal sequences of consecutive alphabetical characters.

        Args:
            return_set (boolean): A flag to indicate whether to return a set of tokens instead of a bag of tokens (defaults to False).

        Attributes:
            return_set (boolean): An attribute that stores the value for the flag return_set.
        """

        def __init__(self, return_set=False):
            self.__al_regex = re.compile('[a-zA-Z]+')
            super(AlphabeticTokenizer, self).__init__(return_set)

        def tokenize(self, input_string):
            """Tokenizes input string into alphabetical tokens.

            Args:
                input_string (str): The string to be tokenized.

            Returns:
                A Python list, which represents a set of tokens if the flag return_set is True, and a bag of tokens otherwise.

            Raises:
                TypeError : If the input is not a string.

            Examples:
                >>> al_tok = AlphabeticTokenizer()
                >>> al_tok.tokenize('data99science, data#integration.')
                ['data', 'science', 'data', 'integration']
                >>> al_tok.tokenize('99')
                []
                >>> al_tok = AlphabeticTokenizer(return_set=True)
                >>> al_tok.tokenize('data99science, data#integration.')
                ['data', 'science', 'integration']
            """
            utils.tok_check_for_none(input_string)
            utils.tok_check_for_string_input(input_string)

            token_list = list(filter(None, self.__al_regex.findall(input_string)))

            if self.return_set:
                return utils.convert_bag_to_set(token_list)

            return token_list