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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_isoelectric_point(seq, granularity=0.1):
 """Calculates the isoelectric point of the sequence for ph 1-13. Parameters seq : str Sequence of amino acids. granularity : float, optional """

    if 'X' in seq:
        warnings.warn(_nc_warning_str, NoncanonicalWarning)
    ph_range, charge_at_ph = charge_series(seq, granularity)
    abs_charge_at_ph = [abs(ch) for ch in charge_at_ph]
    pi_index = min(enumerate(abs_charge_at_ph), key=lambda x: x[1])[0]
    return ph_range[pi_index]