handling modules in packages

[Tommy Grav]

Hi,

   I am working on a package that contains a number of
different modules:

 > ls pyAstro
__init__.py
constants.py
conversion.py
observation.py
orbit.py
transformation.py

however, I find that several of the modules have the
same import statements:

orbit.py:

import numpy
import constants
import conversion
import observations

observations.py:

import numpy
import constants
import conversions
import transformations

The modules themselves are not overly large, but it bugs
me to have to import numpy twice (or even more as the
number of modules grow). Is there a way to import numpy
once in the package (like in the __init__.py file) such that
it is accessible to all the modules? Or is the multiple imports
just something one has to live with?

Thanks for any help or direction to webpages discussing this
topic.

Cheers
   Tommy