def nbins(self, axis=0, overflow=False):
        """
        Get the number of bins along an axis
        """
        if axis == 0:
            nbins = self.GetNbinsX()
        elif axis == 1:
            nbins = self.GetNbinsY()
        elif axis == 2:
            nbins = self.GetNbinsZ()
        else:
            raise ValueError("axis must be 0, 1, or 2")
        if overflow:
            nbins += 2
        return nbins
Get the number of bins along an axis