Interesting issue.

One possible solution is to rename function objects within `RejectionSampler` methods:
```python
class RejectionSampler(object):
    def draw(self):
        q = self.propose_logpdf
        ...
```
But, heck, I was just a few minutes ago advocating **against** introducing new, short names (see `import numpy as np` comments). So I'm really looking forward any discussions about this issue.