Modules and Packages Flashcards

What is `sys.modules`?

Answer: A dictionary caching all currently imported modules

`sys.modules` is a dict mapping module names to module objects; Python checks it first on every import to avoid re-executing module code.

What does `pkgutil.iter_modules()` return?

Answer: An iterator of `(finder, name, ispkg)` tuples for modules in given paths

`pkgutil.iter_modules(path)` yields named tuples describing each module or subpackage found in the given list of directories.

Which attribute of a module object stores the file path where the module was loaded from?

Answer: __file__

`module.__file__` is the absolute path to the `.py` (or `.pyc`) file that was executed to create the module.

When is `__init__.py` code executed?

Answer: The first time the package or any of its submodules is imported

`__init__.py` runs once on the first import of the package; subsequent imports use the cached module from `sys.modules`.

What is the difference between a regular package and a namespace package?

Answer: A regular package has `__init__.py`; a namespace package does not and can span multiple directories

Regular packages require `__init__.py`; namespace packages (PEP 420) lack it and allow merging directories across multiple locations into one logical package.

What does setting `sys.path.insert(0, '/my/path')` accomplish?

Answer: Makes Python search `/my/path` before all other directories when importing

Inserting at index 0 places the path at the front of `sys.path`, so Python finds modules there before any other location.

Which built-in function returns a list of names defined in a module?

Answer: dir()

`dir(module)` returns a sorted list of names in the module's namespace, including functions, classes, and variables.