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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def calculate_base_sequence(base_offsets):
 """ Return a sequence of characters corresponding to the specified base. Example:: '0123456789ABCDEF' @param base_offsets: a list of character offsets in the form of tuples ``(x, y)`` where ``x`` corresponds to the first character of a sequence and ``y`` to the last character of this sequence. @return a sequence of characters, i.e., a string, corresponding to the specified base. """

    return ''.join([ chr(c) for c in list(itertools.chain.from_iterable(
                      [ range(ord(x), ord(y) + 1) for (x, y) in base_offsets ])) ])