python技能实践系列（六）--python内置函数zip源码查看

python内置函数有两种，一种是python实现的，一种是C语言实现的。

• python实现的
  – 1.直接在IDE里面按住ctrl追踪到源码。
  – 2.使用help内置函数，例如：help(os)
• C语言实现的
  不能直接在IDE里面查看
  比如 builtins.py里的zip ,需要去Cpython 源码中查看：
  https://github.com/python/cpython/blob/master/Python/bltinmodule.c

typedef struct {
    PyObject_HEAD
    Py_ssize_t          tuplesize;
    PyObject *ittuple;                  /* tuple of iterators */
    PyObject *result;
} zipobject;

static PyObject *
zip_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    zipobject *lz;
    Py_ssize_t i;
    PyObject *ittuple;  /* tuple of iterators */
    PyObject *result;
    Py_ssize_t tuplesize;

    if (type == &PyZip_Type && !_PyArg_NoKeywords("zip", kwds))
        return NULL;

    /* args must be a tuple */
    assert(PyTuple_Check(args));
    tuplesize = PyTuple_GET_SIZE(args);

    /* obtain iterators */
    ittuple = PyTuple_New(tuplesize);
    if (ittuple == NULL)
        return NULL;
    for (i=0; i < tuplesize; ++i) {
        PyObject *item = PyTuple_GET_ITEM(args, i);
        PyObject *it = PyObject_GetIter(item);
        if (it == NULL) {
            if (PyErr_ExceptionMatches(PyExc_TypeError))
                PyErr_Format(PyExc_TypeError,
                    "zip argument #%zd must support iteration",
                    i+1);
            Py_DECREF(ittuple);
            return NULL;
        }
        PyTuple_SET_ITEM(ittuple, i, it);
    }

    /* create a result holder */
    result = PyTuple_New(tuplesize);
    if (result == NULL) {
        Py_DECREF(ittuple);
        return NULL;
    }
    for (i=0 ; i < tuplesize ; i++) {
        Py_INCREF(Py_None);
        PyTuple_SET_ITEM(result, i, Py_None);
    }

    /* create zipobject structure */
    lz = (zipobject *)type->tp_alloc(type, 0);
    if (lz == NULL) {
        Py_DECREF(ittuple);
        Py_DECREF(result);
        return NULL;
    }
    lz->ittuple = ittuple;
    lz->tuplesize = tuplesize;
    lz->result = result;

    return (PyObject *)lz;
}

static void
zip_dealloc(zipobject *lz)
{
    PyObject_GC_UnTrack(lz);
    Py_XDECREF(lz->ittuple);
    Py_XDECREF(lz->result);
    Py_TYPE(lz)->tp_free(lz);
}

static int
zip_traverse(zipobject *lz, visitproc visit, void *arg)
{
    Py_VISIT(lz->ittuple);
    Py_VISIT(lz->result);
    return 0;
}

static PyObject *
zip_next(zipobject *lz)
{
    Py_ssize_t i;
    Py_ssize_t tuplesize = lz->tuplesize;
    PyObject *result = lz->result;
    PyObject *it;
    PyObject *item;
    PyObject *olditem;

    if (tuplesize == 0)
        return NULL;
    if (Py_REFCNT(result) == 1) {
        Py_INCREF(result);
        for (i=0 ; i < tuplesize ; i++) {
            it = PyTuple_GET_ITEM(lz->ittuple, i);
            item = (*Py_TYPE(it)->tp_iternext)(it);
            if (item == NULL) {
                Py_DECREF(result);
                return NULL;
            }
            olditem = PyTuple_GET_ITEM(result, i);
            PyTuple_SET_ITEM(result, i, item);
            Py_DECREF(olditem);
        }
    } else {
        result = PyTuple_New(tuplesize);
        if (result == NULL)
            return NULL;
        for (i=0 ; i < tuplesize ; i++) {
            it = PyTuple_GET_ITEM(lz->ittuple, i);
            item = (*Py_TYPE(it)->tp_iternext)(it);
            if (item == NULL) {
                Py_DECREF(result);
                return NULL;
            }
            PyTuple_SET_ITEM(result, i, item);
        }
    }
    return result;
}

static PyObject *
zip_reduce(zipobject *lz, PyObject *Py_UNUSED(ignored))
{
    /* Just recreate the zip with the internal iterator tuple */
    return Py_BuildValue("OO", Py_TYPE(lz), lz->ittuple);
}

static PyMethodDef zip_methods[] = {
    {"__reduce__",   (PyCFunction)zip_reduce,   METH_NOARGS, reduce_doc},
    {NULL,           NULL}           /* sentinel */
};

PyDoc_STRVAR(zip_doc,
"zip(iter1 [,iter2 [...]]) --> zip object\n\
\n\
Return a zip object whose .__next__() method returns a tuple where\n\
the i-th element comes from the i-th iterable argument.  The .__next__()\n\
method continues until the shortest iterable in the argument sequence\n\
is exhausted and then it raises StopIteration.");

PyTypeObject PyZip_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "zip",                              /* tp_name */
    sizeof(zipobject),                  /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    (destructor)zip_dealloc,            /* tp_dealloc */
    0,                                  /* tp_print */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_reserved */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE,            /* tp_flags */
    zip_doc,                            /* tp_doc */
    (traverseproc)zip_traverse,    /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    (iternextfunc)zip_next,     /* tp_iternext */
    zip_methods,                        /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    PyType_GenericAlloc,                /* tp_alloc */
    zip_new,                            /* tp_new */
    PyObject_GC_Del,                    /* tp_free */
};