Got unexpected keyword argument - python-2.7

Question

I am trying to practice examples from PyNN website. The code is as follows
import pyNN.brian as p
rng = p.NumpyRNG(seed = 4242)
refractory_period = p.RandomDistribution('uniform', [2.0, 3.0], rng)
ctx_parameters = {'cm': 0.25, 'tau_m': 20.0, 'v_rest': -60, 'v_thresh': -50, 'tau_refrac': refractory_period, 'v_reset': -60, 'v_spike': -50.0, 'a': 1.0, 'b': 0.005, 'tau_w': 600, 'delta_T': 2.5,'tau_syn_E': 5.0, 'e_rev_E': 0.0, 'tau_syn_I': 10.0, 'e_rev_I': -80 }
tc_parameters = ctx_parameters.copy()
tc_parameters.update({'a': 20.0, 'b': 0.0})
thalamocortical_type = p.EIF_cond_exp_isfa_ista(**tc_parameters)
At this point i get an error saying:
Traceback (most recent call last):
File "/home/ruthvik/Desktop/Summer 2017/pynncheck.py", line 7, in <module>
thalamocortical_type = p.EIF_cond_exp_isfa_ista(**tc_parameters)
TypeError: __init__() got an unexpected keyword argument 'tau_refrac'
I actually checked the pyNN github page and i realized that there is in fact a class called EIF_cond_exp_isfa_ista and it also has the parameter 'tau_refrac'. I am not very comfortable with python classes and object orientation. It will be a great help if someone can guide through this.
Edit:
I defined c = p.EIF_cond_exp_isfa_ista. I performed
c.get_parameter_names()
['tau_refrac', 'a', 'tau_m', 'e_rev_E', 'i_offset', 'cm', 'delta_T', 'e_rev_I', 'v_thresh', 'b', 'tau_syn_E', 'v_reset', 'v_spike', 'tau_syn_I', 'tau_w', 'v_rest']
Which gave the above result. I tried to do this
getattr(c,'cm')
Traceback (most recent call last):
File "<pyshell#55>", line 1, in <module>
getattr(c,'cm')
AttributeError: type object 'EIF_cond_exp_isfa_ista' has no attribute 'cm'
I see that there is a parameter called 'cm' but getattr(c,'cm') is throwing an error. I think I'm missing something here.