How to clean a module?

It assumes that there is a module A which have two global variables X
and Y. If I run "import A" in the IDLE shell, then I can use A.X and
A.Y correctly. But if I want to change the module A and then delete
the variable Y, I find I can use A.Y just the same as before!
In fact, I have tried all the following methods but can't remove the
A.Y:
execute "import A" again
"reload(A)"
"del A; import A"
Yes, if you use "del A.Y", it works. But it is stupid since there are
probably many names. In my thought, if no one references objects in A,
"del A" will release all memory about A. But it seems that the fact is
not. So I can not refresh the namespace to follow changes of a module
easily and I will worry about the memory if I del a module.
I want to know if there is a way to clear a module entirely.

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