'Normalising constant for kernel (integral from -inf to inf)'

@property
def norm_const(self):

    if (self._normconst is None):
        if (self.domain is None):
            quadres = scipy.integrate.quad(self._shape, (- inf), inf)
        else:
            quadres = scipy.integrate.quad(self._shape, self.domain[0], self.domain[1])
        self._normconst = (1.0 / quadres[0])
    return self._normconst
