PyMC: Directly changing an object's name doesn't apply when pulling out traces

Question

Here is a bare bit of code which produces an error:

import pymc
import numpy as np

a = pymc.Normal('a', 1, 1)
b = np.empty(4, dtype=object)

for i in range(4):
    b[i] = 1*a
    b[i].__name__ = 'b_%i'%i

M = pymc.MCMC([a,b])
M.sample(10)
M.trace('b_0')        # Causes a KeyError:'b_0'

I don't understand why I get a KeyError: 'b_0' when I try to extract the trace of b_0 and all the other b's. Are the traces just not being saved? If so, is there a way to directly flick some switch to change that without having to make the object using @deterministic.

Answer 1

I looked through it, apparently the trace wasn't being saved. Also, the "flag variable" for keeping the trace isn't .trace, it's .keep_trace