One module per class, bad idea?

[Matias Jansson]

I come from a background of Java and C# where it is common practise to have 
one class per file in the file/project structure. As I have understood it, 
it is more common practice to have many classes in a Python module/file. 
What is the motivation behind it, would it be a bad idea to have a guideline 
in your project that promotes a one class per file structure (assuming most 
of the programmers a background similar to mine)?