What steps will reproduce the problem?
1. $  cd aima-python
2. $ python
3.  >>> import agents
4.  >>> v = VacuumEnvironment()
5. >>> e = EnvGUI(v)

What is the expected output?

Some Tkinkter window with the Environment

 What do you see instead?

An empty Tkinkter window and an error message at the repl:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/rickard/devel/ArtificialIntelligence/aima/aima-python/agents.py", line 617, in 
__init__
    canvas = EnvCanvas(self, env, cellwidth, n)
NameError: global name 'EnvCanvas' is not defined

What version of the product are you using? On what operating system?

Svn revision 29 from Google Code on Mac OS X 10.4.11

Please provide any additional information below.

The commentary at the top of the agents.py file mentions the EnvCanvas class 
but the file 
doesn't contain a definition of it. Perhaps it is left as an excercise for the 
reader.. :-)