A namespace package built from two folders
There is no __init__.py anywhere, yet import plugins works, and it combines the two plugins folders. Its __file__ is None because no single file defines it. sys.path[:0] = [...] is slice assignment (Topic 4.2): it puts the two folders at the front of the search list.
A package is a folder of modules that you import as one unit. Its __init__.py runs on import and decides what the package shows to the outside, absolute imports name the full path from the top, relative imports use dots, and circular imports are fixed by changing who imports whom.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
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Practice questions
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Create a package zoo: a folder zoo with an empty __init__.py, and a module zoo/cat.py that contains SOUND = "meow". Then write the code that imports cat from zoo and prints cat.SOUND.
Change the __init__.py of your zoo package so that SOUND is available directly. After your change, from zoo import SOUND must work.
Write the relative-import line that zoo/dog.py would use to import SOUND from its sibling cat.py.
Explain it without notes
What is a package, and what does __init__.py do?
What is the difference between absolute and relative imports? When does each fail?
What is __all__ for?
What causes a circular import error, and how do you fix it?
Expected output
has __init__.py: False
namespace parts: ['plugins/one', 'plugins/two']
alpha beta