Relative Import Beyond Top-Level Package

When attempting relative imports within a multi-level Python package, running the module from the package directory can result in the "ValueError: attempted relative import beyond top-level package" error. Understanding the reason behind this error is crucial for effective package management.

The error occurs because Python does not maintain a record of where packages are loaded from. Executing a module as "python -m test_A.test" essentially informs Python that test_A.test is not located within a package (despite it residing in package/test_A). Consequently, attempting "from ..A import foo" becomes invalid as Python lacks knowledge of test_A being part of a larger package.

In contrast, using "python -m package.test_A.test" preserves the hierarchical structure and allows "from ..A import foo" to resolve successfully. It accurately reflects the fact that test_A is a child directory within the loaded package "package."

The underlying reason why Python does not consider the current working directory to be a package is unknown. However, this limitation can be alleviated by explicitly declaring directories as packages using the "__init__.py" file and adhering to Python's package lookup mechanism when importing modules.