什么是python的_random？

Question

如果你打开random.py它看它是如何工作的,它的类Random子类_random.Random:

import _random

class Random(_random.Random):
    """Random number generator base class used by bound module functions.

    Used to instantiate instances of Random to get generators that don't
    share state.  Especially useful for multi-threaded programs, creating
    a different instance of Random for each thread, and using the jumpahead()
    method to ensure that the generated sequences seen by each thread don't
    overlap.

    Class Random can also be subclassed if you want to use a different basic
    generator of your own devising: in that case, override the following
    methods: random(), seed(), getstate(), setstate() and jumpahead().
    Optionally, implement a getrandbits() method so that randrange() can cover
    arbitrarily large ranges.

    """

我可以random.py通过以下方式轻松找到该文件:

In [1]: import sys
In [2]: print random.__file__
/usr/lib/python2.7/random.pyc

但是_random没有这个变量:

In [3]: _random.__file__
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-295-a62b7df330e2> in <module>()
----> 1 _random.__file__

AttributeError: 'module' object has no attribute '__file__'

那么_random,为什么要将它random子类化,哪里可以找到相应的文件？

Answer 1

通常的做法是使用C中实现的模块的前导下划线.通常使用_mod此C模块的模式以及mod导入此模块的Python模块_mod.您可以在标准库的多个模块中找到它.通常,您应该使用mod而不是_mod.

在Mac OS X上有一个文件:

_random.so

在Python使用的共享库的目录中.

只需在交互式提示符下键入模块名称即可查看路径:

>>> _random
>>> <module '_random' from '/path/to/python/sharedlibs/_random.so'>

顺便说一句,并非所有可导入的模块都有与之关联的文件.有些是Python可执行文件的一部分,内置模块:

>>> import sys
>>> sys.builtin_module_names
('_ast', '_codecs', '_collections', '_functools', '_imp', '_io', '_locale',
 '_operator', '_signal', '_sre', '_stat', '_string', '_symtable', '_thread',
 '_tracemalloc', '_warnings', '_weakref', 'atexit', 'builtins', 'errno', 
 'faulthandler', 'gc', 'itertools', 'marshal', 'posix', 'pwd', 'sys', 
 'time', 'xxsubtype', 'zipimport')

所以,如果你进入你的平台:

>>> _random
_random <module '_random' (built-in)>

而不是_randomPython可执行的一部分.

在C source _randommodule.c中,您可以找到Random可在Python中使用的方法:

static PyMethodDef random_methods[] = {
    {"random",          (PyCFunction)random_random,  METH_NOARGS,
        PyDoc_STR("random() -> x in the interval [0, 1).")},
    {"seed",            (PyCFunction)random_seed,  METH_VARARGS,
        PyDoc_STR("seed([n]) -> None.  Defaults to current time.")},
    {"getstate",        (PyCFunction)random_getstate,  METH_NOARGS,
        PyDoc_STR("getstate() -> tuple containing the current state.")},
    {"setstate",          (PyCFunction)random_setstate,  METH_O,
        PyDoc_STR("setstate(state) -> None.  Restores generator state.")},
    {"getrandbits",     (PyCFunction)random_getrandbits,  METH_VARARGS,
        PyDoc_STR("getrandbits(k) -> x.  Generates an int with "
                  "k random bits.")},
    {NULL,              NULL}           /* sentinel */
};

相比于:

>>> [x for x in dir(_random.Random) if not x.startswith('__')]
['getrandbits', 'getstate', 'jumpahead', 'random', 'seed', 'setstate']