'Add other to self pointwise.
Requires that both self and other are of the same length, and contain
identical timestamps. Typically this means that Normalize has been called
on both with identical time parameters.
Args:
other: The sequence to add to self.
Raises:
RuntimeError: other does not contain the same timestamps as self.'

def Add(self, other):

    if (len(self.data) != len(other.data)):
        raise RuntimeError('Can    only    add    series    of    identical    lengths.')
    for i in range(len(self.data)):
        if (self.data[i][1] != other.data[i][1]):
            raise RuntimeError('Timestamp    mismatch.')
        if ((self.data[i][0] is None) and (other.data[i][0] is None)):
            continue
        self.data[i][0] = ((self.data[i][0] or 0) + (other.data[i][0] or 0))
