find out whether a module exists (without importing it)

[Miki Tebeka]

> imp.find_module(), but
> it didn't find any module name containing a '.'
The docs (http://docs.python.org/library/imp.html#imp.find_module) clearly say:

"This function does not handle hierarchical module names (names containing dots). In order to find P.M, that is, submodule M of package P, use find_module() and load_module() to find and load package P, and then use find_module() with the path argument set to P.__path__. When P itself has a dotted name, apply this recipe recursively."

See https://gist.github.com/3278829 for possible implementation.