Recursive dependencies of imported libraries

When importing certain libraries that include other recursive dependencies, these are not imported.

For example, if my script is:
```

import sklearn

print("Hello")
```

`requirements.txt` will include:
`sklearn = 0.18`

Which is insufficient since, in this case, [numpy and Scipy are also required](http://scikit-learn.org/stable/install.html).

Would be possible to amend these kind of issues?