Multiple classes in a Python module
It is absolutely proper to do so. A module groups related functionality. If that functionality is implemented in several classes (e.g., Tree, Node, Leaf) then it is appropriate to place them together. 
A module is more closely associated with a Java package than a Java class. You can also implement a module as a folder, named for the module, with an __init__.py file inside (so Python can identify the module as such; the __init__.py may also optionally include initialization code and lists of classes, functions, and sub-packages to export.)
I'm very new to Python (I'm coming from a JAVA background) and I'm wondering if anyone could help me with some of the Python standards. Is it a normal or "proper" practice to put multiple class in a module? I have been working with Django and started with the tutorials and they place their database model classes in the same module. Is this something that is normally done or should I stick with 1 class per module? Is there a reason I would do one over the other?
Hope I'm being clear and not to generic. Thanks to everyone in advance!