newbie question: how to run a python file if it is in a package

[neoedmund]

for example:

X.py is in aaa.bbb and it has a line like "import aaa.bbb.Y"
how can I run X.py avoiding it saying such like "ImportError: No
module named aaa.bbb"?

Is all runnable script must be in the default package?

thanks.
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