What does a . in an import statement in Python mean?

I'm looking over the code for Python's multiprocessing module, and it contains this line:

from ._multiprocessing import win32, Connection, PipeConnection

instead of

from _multiprocessing import win32, Connection, PipeConnection

the subtle difference being the period before _multiprocessing. What does that mean? Why the period?

That's the new syntax for explicit relative imports. It means import from the current package.

The dot in the module name is used for relative module import (see here and here, section 6.4.2).

You can use more than one dot, referring not to the curent package but its parent(s). This should only be used within packages, in the main module one should always use absolute module names.