Module Lookup Rules Summary

With packages and relative imports, the module search story in Python 3.0 in its entirety can be summarized as follows:

 

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  • Simple module names (e.g., A) are looked up by searching each directory on the sys.path list, from left to right. This list is constructed from both system defaults and user-configurable settings.
  • Packages are simply directories of Python modules with a special __init__.py file, which enables A.B.C directory path syntax in imports. In an import of A.B.C, for example, the directory named A is located relative to the normal module import search of sys.path, B is another package subdirectory within A, and C is a module or other importable item within B.
  • Within a package’s files, normal import statements use the same sys.path search rule as imports elsewhere. Imports in packages using from statements and leading dots, however, are relative to the package; that is, only the package directory is checked, and the normal sys.path lookup is not used. In from . import A, for example, the module search is restricted to the directory containing the file in which this statement appears.