Since a package, like a module, is both a file system location and a Python construct, the name must be a valid Python name, using just letters, numbers and _'s. Additionally, some file systems are cavalier about maintaining the original case of the filename. The old Mac OS (pre Mac OS X), and many of the old Windows variants would casually alter the case of filenames.

Consequently, package and module names should be all lower case. This way, there is no ambiguity about the intended case of the module name.

Package structures should be relatively flat. The general rule is to keep the package structure relatively flat. Having only one module at the bottom of deeply-nested packages isn't really very informative or helpful. While it may seem like import casino.games.definitions.tablegames.dicegames.craps leaves lots of room for expansion, there just aren't enough casino games to make this immensly deep structure usable.

Packages are generally used for two things:

If all of your modules are more-or-less unique, then a package structure isn't going to help. Similarly, if you don't have alternate implementations of some driver or interface, a package structure isn't useful.