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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 sequence_molar_extinction_280(seq):
 """Returns the molar extinction coefficient of the sequence at 280 nm. Notes ----- Units = M/cm Parameters seq : str Sequence of amino acids. """

    if 'X' in seq:
        warnings.warn(_nc_warning_str, NoncanonicalWarning)
    return sum([residue_ext_280[aa] * n for aa, n in Counter(seq).items()])