Re: baffling error-handling problem

Chris Fonnesbeck wrote: 
I thought I knew how to do error handling in python, but apparently I
dont. I have a bunch of code to calculate statistical likelihoods, and
use error handling to catch invalid parameters. For example, for the
bernoulli distribution, I have:

    def bernoulli_like(self, x, p, name='bernoulli'):
        ... if sum(p>=1 or p<=0): raise LikelihoodError ...

where LikelihoodError is simply a subclass of ValueError that I created:

    class LikelihoodError(ValueError):
        "Log-likelihood is invalid or negative infinite"

I catch these errors with the following:

        try: like = self.calculate_likelihood()
        except LikelihoodError:
            return 0

> ... [when using] ... 
     like=self.bernoulli_like(x,p)

I get the following when an invalid parameter is passed:

Traceback (most recent call last):
  File "...\model_000.py", line 381, in ?
    model.sample(iterations=iter, burn=burn,plot=False)
  File "...\PyMC\MCMC.py", line 1691, in sample
    self._like = self.calculate_likelihood()
  File "...\model_000.py", line 194, in calculate_likelihood
    like+=self.bernoulli_like(x,p)
  File "...\MCMC.py", line 868, in bernoulli_like
    if sum(p>=1 or p<=0): raise LikelihoodError
LikelihoodError

I have no idea how this can happen, given how I have coded this. 

Might you be referring to a different LikelihoodError in the
  try: ... except ... part of your code than in the ... raise ... part?
Similarly defined classes are not the same class.  If you didn't
get LikelihoodError in mode4l_000.py with the moral equivalent of
     from MCMC import LikelihoodError
then this is what is going wrong.
By the way, if it were I, I'd:    raise LikelihoodError(p)  just so I
could discover a bit of what went wrong.

--Scott David Daniels
Scott.Daniels@xxxxxxx
.