# Sequence Protocol

int `PySequence_Check`(PyObject *o)

  Return `1` if the object provides sequence protocol, and `0` otherwise. Note that it returns `1` for Python classes with a `__getitem__()` method unless they are `dict` subclasses since in general case it is impossible to determine what the type of keys it supports. This function always succeeds.

Py_ssize_t `PySequence_Size`(PyObject *o)
Py_ssize_t `PySequence_Length`(PyObject *o)

  Returns the number of objects in sequence o on success, and `-1` on failure. This is equivalent to the Python expression `len(o)`.

PyObject* `PySequence_Concat`(PyObject *o1, PyObject *o2)
  Return value: New reference.

  Return the concatenation of o1 and o2 on success, and NULL on failure. This is the equivalent of the Python expression `o1 + o2`.

PyObject* `PySequence_Repeat`(PyObject *o, Py_ssize_t count)
  Return value: New reference.

  Return the result of repeating sequence object o count times, or NULL on failure. This is the equivalent of the Python expression `o * count`.

PyObject* `PySequence_InPlaceConcat`(PyObject *o1, PyObject *o2)
  Return value: New reference.

  Return the concatenation of o1 and o2 on success, and NULL on failure. The operation is done in-place when o1 supports it. This is the equivalent of the Python expression `o1 += o2`.

PyObject* `PySequence_InPlaceRepeat`(PyObject *o, Py_ssize_t count)
  Return value: New reference.

  Return the result of repeating sequence object o count times, or NULL on failure. The operation is done in-place when o supports it. This is the equivalent of the Python expression `o *= count`.

PyObject* `PySequence_GetItem`(PyObject *o, Py_ssize_t i)
  Return value: New reference.

  Return the ith element of o, or NULL on failure. This is the equivalent of the Python expression `o[i]`.

PyObject* `PySequence_GetSlice`(PyObject *o, Py_ssize_t i1, Py_ssize_t i2)
  Return value: New reference.

  Return the slice of sequence object o between i1 and i2, or NULL on failure. This is the equivalent of the Python expression `o[i1:i2]`.

int `PySequence_SetItem`(PyObject *o, Py_ssize_t i, PyObject *v)

  Assign object v to the ith element of o. Raise an exception and return `-1` on failure; return `0` on success. This is the equivalent of the Python statement `o[i] = v`. This function does not steal a reference to v.

  If v is NULL, the element is deleted, however this feature is deprecated in favour of using `PySequence_DelItem()`.

int `PySequence_DelItem`(PyObject *o, Py_ssize_t i)

  Delete the ith element of object o. Returns `-1` on failure. This is the equivalent of the Python statement `del o[i]`.

int `PySequence_SetSlice`(PyObject *o, Py_ssize_t i1, Py_ssize_t i2, PyObject *v)

  Assign the sequence object v to the slice in sequence object o from i1 to i2. This is the equivalent of the Python statement `o[i1:i2] = v`.

int `PySequence_DelSlice`(PyObject *o, Py_ssize_t i1, Py_ssize_t i2)

  Delete the slice in sequence object o from i1 to i2. Returns `-1` on failure. This is the equivalent of the Python statement `del o[i1:i2]`.

Py_ssize_t `PySequence_Count`(PyObject *o, PyObject *value)

  Return the number of occurrences of value in o, that is, return the number of keys for which `o[key] == value`. On failure, return `-1`. This is equivalent to the Python expression `o.count(value)`.

int `PySequence_Contains`(PyObject *o, PyObject *value)

  Determine if o contains value. If an item in o is equal to value, return `1`, otherwise return `0`. On error, return `-1`. This is equivalent to the Python expression `value in o`.

Py_ssize_t `PySequence_Index`(PyObject *o, PyObject *value)

  Return the first index i for which `o[i] == value`. On error, return `-1`. This is equivalent to the Python expression `o.index(value)`.

PyObject* `PySequence_List`(PyObject *o)
  Return value: New reference.

  Return a list object with the same contents as the sequence or iterable o, or NULL on failure. The returned list is guaranteed to be new. This is equivalent to the Python expression `list(o)`.

PyObject* `PySequence_Tuple`(PyObject *o)
  Return value: New reference.

  Return a tuple object with the same contents as the sequence or iterable o, or NULL on failure. If o is a tuple, a new reference will be returned, otherwise a tuple will be constructed with the appropriate contents. This is equivalent to the Python expression `tuple(o)`.

PyObject* `PySequence_Fast`(PyObject *o, const char *m)
  Return value: New reference.

  将序列或可迭代对象 o 作为其他 `PySequence_Fast*` 函数家族可用的对象返回。 如果该对象不是序列或可迭代对象，则会引发 `TypeError` 并将 m 作为消息文本。 失败时返回 NULL。

  `PySequence_Fast*` 函数之所以这样命名，是因为它们会假定 o 是一个 `PyTupleObject` 或 `PyListObject` 并直接访问 o 的数据字段。

  作为 CPython 的实现细节，如果 o 已经是一个序列或列表，它将被直接返回。

Py_ssize_t `PySequence_Fast_GET_SIZE`(PyObject *o)

  Returns the length of o, assuming that o was returned by `PySequence_Fast()` and that o is not NULL. The size can also be gotten by calling `PySequence_Size()` on o, but `PySequence_Fast_GET_SIZE()` is faster because it can assume o is a list or tuple.

PyObject* `PySequence_Fast_GET_ITEM`(PyObject *o, Py_ssize_t i)
  Return value: Borrowed reference.

  Return the ith element of o, assuming that o was returned by `PySequence_Fast()`, o is not NULL, and that i is within bounds.

PyObject** `PySequence_Fast_ITEMS`(PyObject *o)

  Return the underlying array of PyObject pointers. Assumes that o was returned by `PySequence_Fast()` and o is not NULL.

  Note, if a list gets resized, the reallocation may relocate the items array. So, only use the underlying array pointer in contexts where the sequence cannot change.

PyObject* `PySequence_ITEM`(PyObject *o, Py_ssize_t i)
  Return value: New reference.

  返回 o 的第 i 个元素或在失败时返回 NULL。 此形式比 `PySequence_GetItem()` 更快，但不会检查 o 的 `PySequence_Check()` 是否为真，也不会对负序号进行调整。