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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 numberOfProximalSynapses(self, cells=None):
 """ Returns the number of proximal synapses with permanence>0 on these cells. Parameters: @param cells (iterable) Indices of the cells. If None return count for all cells. """

    if cells is None:
      cells = xrange(self.numberOfCells())

    n = 0
    for cell in cells:
      n += self.proximalPermanences.nNonZerosOnRow(cell)
    return n