为什么模块数学被称为“内建”？

Question

AFAIK，Pythonbuiltins指的是__builtins__中包含的那些异常和函数：

>>> import builtins  # import __builtin__ in Python 2
>>> dir(builtins)  # dir(__builtin__) for Python 2
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException',
'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning',
...many more...
'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed',
'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum',
'super', 'tuple', 'type', 'vars', 'zip']

但是看看下面的代码（Python2和3都给出了相同的结果）：

^{pr2}$

在最后一行，模块math被称为built-in。为什么？模块math和其他模块如threading有什么区别？在

Answer 1

从文档（./Doc/library/stdtypes.rst）中：

Modules

...

Modules built into the interpreter are written like this: <module 'sys' (built-in)>. If loaded from a file, they are written as <module 'os' from '/usr/local/lib/pythonX.Y/os.pyc'>.

相关代码位于模块对象的repr()函数中：

static PyObject *
module_repr(PyModuleObject *m)
{
    char *name;
    char *filename;

    name = PyModule_GetName((PyObject *)m);
    if (name == NULL) {
        PyErr_Clear();
        name = "?";
    }
    filename = PyModule_GetFilename((PyObject *)m);
    if (filename == NULL) {
        PyErr_Clear();
        return PyString_FromFormat("<module '%s' (built-in)>", name);
    }
    return PyString_FromFormat("<module '%s' from '%s'>", name, filename);
}

Answer 2

在您的例子中，math模块在构建库时包含在主Python库本身（libpython2.7.{so,dll,dylib}）中。这是可能的，因为模块是用C编写的，而不是用纯Python编写的。其他类似的模块包括sys和{}。在

Answer 3

Python docs有这样的话：

The bulk of the library, however, consists of a collection of modules. There are many ways to dissect this collection. Some modules are written in C and built in to the Python interpreter; others are written in Python and imported in source form.

math模块是用C语言编写的，它被构建到解释器中，而threading是用Python编写的，并在源代码中导入。在