What is the default binding to the `__import__` at

问题:

From Python in a Nutshell

Custom Importers

An advanced, rarely needed functionality that Python offers is the ability to change the semantics of some or all import and from statements.

Rebinding __import__

You can rebind the __import__ attribute of the module builtin to your own custom importer function—for example, one using the generic built-in-wrapping technique shown in “Python built-ins” on page 174.

1. In "You can rebind the __import__ attribute of the module builtin", should "the module builtin" be "the module builtins" instead?

2. Is "the __import__ attribute of the module builtin" bound to importlib.__import__function by default? Or does "the module builtin" provide the default implementation bound to its __import__ attribute?

回答1:

1. Yes, that's a typo in the book. In Python 2 the same module is named __builtin__ (no s), in Python 3 it is named builtins.

2. builtins.__import__ is a distinct function from importlib.__import__. If you are going to rebind builtins.__import__, save a reference.

   • builtins.__import__ is implemented in C, and essentially calls the C-API PyImport_ImportModuleLevelObject function.

   • importlib.__import__ is a pure-Python function. The goal of importlib is to provide a pure-python implementation of the import machinery so it can be hacked on more easily, and this function is no exception.