# Sequence Protocol

int PySequence_Check(PyObject *o)
  Part of the Stable ABI.

  Return `1` if the object provides the 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 it is impossible to determine what type of keys the class supports. This function always succeeds.

Py_ssize_t PySequence_Size(PyObject *o)
Py_ssize_t PySequence_Length(PyObject *o)
  Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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, but this feature is deprecated in favour of using `PySequence_DelItem()`.

int PySequence_DelItem(PyObject *o, Py_ssize_t i)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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`.

int PySequence_In(PyObject *o, PyObject *value)
  Part of the Stable ABI.

  Alias for `PySequence_Contains()`.

  Soft deprecated since version 3.14: The function should no longer be used to write new code.

Py_ssize_t PySequence_Index(PyObject *o, PyObject *value)
  Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  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. Part of the Stable ABI.

  Return the sequence or iterable o as an object usable by the other `PySequence_Fast*` family of functions. If the object is not a sequence or iterable, raises `TypeError` with m as the message text. Returns `NULL` on failure.

  The `PySequence_Fast*` functions are thus named because they assume o is a `PyTupleObject` or a `PyListObject` and access the data fields of o directly.

  As a CPython implementation detail, if o is already a sequence or list, it will be returned.

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 retrieved 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.

  Return the ith element of o or `NULL` on failure. Faster form of `PySequence_GetItem()` but without checking that `PySequence_Check()` on o is true and without adjustment for negative indices.