sys.path is a list of directory names that Python searches when locating an importable module or package. Python checks the directories in order and stops at the first matching file. section 9.1
Inspecting the import search path
Use sys.path to see the directories Python will search: `import sys` followed by `print(sys.path)`. If two directories contain modules with the same name, the module in the first matching directory wins; later matches are ignored. section 9.1
Keep these import behaviors in mind when diagnosing missing modules or unexpected definitions:
- Import the module name, not its filename: use `import os`, rather than `import os.py`. section 9.1
- Place a package directory somewhere on sys.path before importing modules such as `mypackage.first`. section 9.9
- Change the search path through PYTHONPATH or `.pth` files in the installation’s site-packages directory. section 9.5
- Separate search from loading: Python consults sys.modules to avoid loading an already loaded module again. section 9.5
