Examples can be found here
or one can use
Sd_gp_len_scale = expected_length_scale_list
GP_len_scale = []
for i in range(len(Sd_gp_len_scale)):
GP_len_scale.append(pm.HalfNormal('GP_len_scale['+str(i)+']',
sigma = Sd_gp_len_scale[i])) #one can substitute their own variable names and distributions