class MarkovChain:
    """
    Entity which contains a chunk of text and a Markov chain generated from it.
    """
    def __init__(self, text):
        self.text = text

    def pair_symbols(self, text):
        return [pair for pair in zip(text[0::1], text[1::1])]

class MarkovChain:
    """
    Entity which contains a chunk of text and a Markov chain generated from it.
    """
    def __init__(self, text):
        self.text = text

    def pair_symbols(self, text):
        """
        Takes an string and returns a list of tuples. For example:

            >>> pair_symbols('Arya')
            [('A', 'r'), ('r', 'y'), ('y', 'a')]
        """
        return [pair for pair in zip(text[0::1], text[1::1])]

Add docstring to the `pair_symbols` method