Created import and importlib notes (markdown)

import-and-importlib-notes.md

@@ -0,0 +1,116 @@
+```
+class module:
+    __name__        # Full qualified name. Required.
+    __loader__      # Loader object used to load the module. Required. Deprecated.
+    __package__     # If the module is a package, same as __name__.
+                    # Otherwise name of parent package, or empty string for
+                    # top-level module. Optional.
+    __spec__        # ModuleSpec object. Required (except sometimes for __main__).
+    __path__        # Search path for modules inside package. Required iif a package.
+                    # Presence of __path__ indicates a package.
+                    # Iterable type other than list indicates a namespace package (PEP 420)
+    __file__        # Path of the file (if any) the module was loaded from. Optional.
+    __cached__      # Path of cached bytecode (if any) for the module. Optional.
+
+class importlib._bootstrap.BuiltinImporter
+    def is_package(cls, fullname) -> False:
+        "built-in modules are never packages."
+
+
+class importlib.abc.MetaPathFinder:
+    def find_spec(fullname, path, target=None)
+        Should return None if this finder can't handle the module.
+        Raise ModuleNotFoundError to halt any further search for the module.
+    def invalidate_caches()  # Optional
+
+class importlib.abc.Loader:
+    def create_module(spec)
+        Return a created module object, or None if the spec should create it.
+        Raise ImportError if anything prevents creation of the module object.
+    def exec_module(spec)
+        Execute the module. Don't return anything.
+
+class importlib.abc.PathEntryFinder:
+    def find_spec(fullname, target=None)
+    def invalidate_caches()  # Optional
+
+
+importlib.machinery.ModuleSpec:  # Python 3.4+
+    name            # __name__
+    loader          # __loader__
+    origin          # __file__
+    submodule_search_locations
+                    # __path__
+                    # None indicates a non-package.
+                    # List (even empty) indicates a package.
+                    # A custom iterable indicates a namespace package.
+    loader_state
+    cached          # __cached__
+    parent          # __package__
+                    # Same as name, if the module is a package.
+                    # Otherwise name of parent package,
+                    # or empty string if a top-level module.
+    has_location    # True if origin refers to a loadable location
+
+importlib.find_loader(name, path=None)  # Python 3.3-3.11
+
+importlib.util._find_spec(name, path, target=None)
+importlib.util.find_spec(name, package=None)  # Python 3.4+
+importlib.util.spec_from_file_location(nmae, location=None, * loader=None,
+                                       submodule_search_locations=...)
+
+_imp module is implemented in https://github.com/python/cpython/blob/3.11/Python/import.c
+
+
+imp.find_module -> (Optional[fobj], Optional[path], (suffix, mode, type_))  # Python 2.x - 3.11
+```
+
+|            | `import.new_module()` | `types.ModuleType()` |
+|------------|-----------------------|----------------------|
+| Python 2.x |  `bytes` or `unicode` |        `bytes`       |
+| Python 3.x |       `unicode`       |       `unicode`      |
+
+```
+ansible_mitogen.module_finder.Module:
+    name    Unqualified name of the module.
+    path    Filesystem path of the module.
+    kind    One of the constants in `imp`, as returned in `imp.find_module()`
+    parent  `ansible_mitogen.module_finder.Module` of parent package (if any).
+
+pkgutil.ModuleInfo(module_finder, name, ispkg)  # namedtuple, Python 3.6+
+pkgutil.find_loader(full_name)          # Deprecated 3.12, removal 3.14
+pkgutil.get_importer(path_item)
+pkgutil.get_loader(module_or_name)      # Deprecated 3.12, removal 3.14
+
+sys.builtin_module_names: tuple         # Python 2.2+, atleast
+sys.stdlib_module_names: frozenset      # Python 3.10, includes platform specific 
+                                        # even if not correct platform
+https://pypi.org/project/stdlibs/
+
+
+Module name must be a valid Python identifier
+    Python 2: r'[A-Za-z_][A-Za-z0-9_]*'
+    Python 3: https://docs.python.org/3/reference/lexical_analysis.html#identifiers
+
+
+Python 2.7:
+    sys.meta_path == []
+    sys.path_hooks == [<type 'zipimport.zipimporter'>]
+
+Python 3.11:
+    sys.meta_path == [
+        <_distutils_hack.DistutilsMetaFinder object at 0x100874e90>,
+        <class '_frozen_importlib.BuiltinImporter'>,
+        <class '_frozen_importlib.FrozenImporter'>,
+        <class '_frozen_importlib_external.PathFinder'>,
+    ]
+    sys.path_hooks == [
+        <class 'zipimport.zipimporter'>,
+        <function FileFinder.path_hook.<locals>.path_hook_for_FileFinder at 0x1007e8900>.
+    ]
+```
+Sources
+* https://docs.python.org/3/library/importlib.html
+* https://peps.python.org/pep-0273/ Import from Zip Archives
+* https://peps.python.org/pep-0302/ Import hooks (sys.meta_path, sys.path_hooks)
+* https://peps.python.org/pep-0451/ ModuleSpec for import hooks