How to do it...

1. When making a package, follow the normal filesystem hierarchy in terms of directory structure; that is, modules that relate to each other should be placed in their own directory.
2. A possible package for a video file handler is shown in package_tree.py:

      video/                  # Top-level package
          __init__.py         # Top-level initialization
          formats/            # Sub-package for file formats
              __init__.py     # Package-level initialization
              avi_in.py
              avi_out.py
              mpg2_in.py
              mpg2_out.py
              webm_in.py
              webm_out.py
          effects/             # Sub-package for video effects
              specialFX/       # Sub-package for special effects
                  __init__.py
                  sepia.py
                  mosaic.py
                  old_movie.py
                  glass.py
                  pencil.py
                  tv.py
              transform/        # Sub-package for transform effects
                  __init__.py
                  flip.py
                  skew.py
                  rotate.py
                  mirror.py
                  wave.py
                  broken_glass.py
              draw/              # Sub-package for draw effects
                  __init__.py
                  rectangle.py
                  ellipse.py
                  border.py
                  line.py
                  polygon.py

1. But, what happens if you were already in the specialFX/ directory and wanted to import from another package? Use relative paths to walk the directory and import using dots, just like changing directories on the command-line:

      from . import mosaic
      from .. import transform
      from .. draw import rectangle