Wheels
I know this is an old question, but wheel packages have since been invented! Since a wheel is simply a zip file that gets extracted into the lib/site-packages directory, an examination of the contents of the wheel archive can give you the top level imports.
>>> import zipfile
>>> zf = zipfile.ZipFile('setuptools-35.0.2-py2.py3-none-any.whl')
>>> top_level = set([x.split('/')[0] for x in zf.namelist()])
>>> # filter out the .dist-info directory
>>> top_level = [x for x in top_level if not x.endswith('.dist-info')]
>>> top_level
['setuptools', 'pkg_resources', 'easy_install.py']
So setuptools actually gives you three top level imports!
pip download
pip now has a download command, so you can simply run pip download setuptools
(or whatever package you like) and then examine it.
Reverse look up
Unfortunately I haven't found an easy way to go the other direction yet. That is, given the import name, what is the package name. This can be a problem if you are looking at some example code or maybe if you use Anaconda that comes with a bunch of packages pre-installed and you want to know the actual package name.
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