# Bytes Objects

These functions raise `TypeError` when expecting a bytes parameter and are called with a non-bytes parameter.

`PyBytesObject`

  This subtype of `PyObject` represents a Python bytes object.

PyTypeObject `PyBytes_Type`

  This instance of `PyTypeObject` represents the Python bytes type; it is the same object as `bytes` in the Python layer.

int `PyBytes_Check`(PyObject *o)

  Return true if the object o is a bytes object or an instance of a subtype of the bytes type.

int `PyBytes_CheckExact`(PyObject *o)

  Return true if the object o is a bytes object, but not an instance of a subtype of the bytes type.

PyObject* `PyBytes_FromString`(const char *v)
  Return value: New reference.

  Return a new bytes object with a copy of the string v as value on success, and NULL on failure. The parameter v must not be NULL; it will not be checked.

PyObject* `PyBytes_FromStringAndSize`(const char *v, Py_ssize_t len)
  Return value: New reference.

  Return a new bytes object with a copy of the string v as value and length len on success, and NULL on failure. If v is NULL, the contents of the bytes object are uninitialized.

PyObject* `PyBytes_FromFormat`(const char *format, ...)
  Return value: New reference.

  Take a C `printf()`-style format string and a variable number of arguments, calculate the size of the resulting Python bytes object and return a bytes object with the values formatted into it. The variable arguments must be C types and must correspond exactly to the format characters in the format string. The following format characters are allowed:

  Format Characters | Type | Comment
  --- | --- | ---
  `%%` | n/a | The literal % character.
  `%c` | int | A single byte, represented as a C int.
  `%d` | int | Equivalent to `printf("%d")`. [1]
  `%u` | unsigned int | Equivalent to `printf("%u")`. [1]
  `%ld` | long | Equivalent to `printf("%ld")`. [1]
  `%lu` | unsigned long | Equivalent to `printf("%lu")`. [1]
  `%zd` | Py_ssize_t | Equivalent to `printf("%zd")`. [1]
  `%zu` | size_t | Equivalent to `printf("%zu")`. [1]
  `%i` | int | Equivalent to `printf("%i")`. [1]
  `%x` | int | Equivalent to `printf("%x")`. [1]
  `%s` | const char* | A null-terminated C character array.
  `%p` | const void* | The hex representation of a C pointer. Mostly equivalent to `printf("%p")` except that it is guaranteed to start with the literal `0x` regardless of what the platform’s `printf` yields.

  An unrecognized format character causes all the rest of the format string to be copied as-is to the result object, and any extra arguments discarded.

  [1] | (1, 2, 3, 4, 5, 6, 7, 8) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the 0-conversion flag has effect even when a precision is given.

PyObject* `PyBytes_FromFormatV`(const char *format, va_list vargs)
  Return value: New reference.

  Identical to `PyBytes_FromFormat()` except that it takes exactly two arguments.

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

  Return the bytes representation of object o that implements the buffer protocol.

Py_ssize_t `PyBytes_Size`(PyObject *o)

  Return the length of the bytes in bytes object o.

Py_ssize_t `PyBytes_GET_SIZE`(PyObject *o)

  Macro form of `PyBytes_Size()` but without error checking.

char* `PyBytes_AsString`(PyObject *o)

  Return a pointer to the contents of o. The pointer refers to the internal buffer of o, which consists of `len(o) + 1` bytes. The last byte in the buffer is always null, regardless of whether there are any other null bytes. The data must not be modified in any way, unless the object was just created using `PyBytes_FromStringAndSize(NULL, size)`. It must not be deallocated. If o is not a bytes object at all, `PyBytes_AsString()` returns NULL and raises `TypeError`.

char* `PyBytes_AS_STRING`(PyObject *string)

  Macro form of `PyBytes_AsString()` but without error checking.

int `PyBytes_AsStringAndSize`(PyObject *obj, char **buffer, Py_ssize_t *length)

  Return the null-terminated contents of the object obj through the output variables buffer and length.

  If length is NULL, the bytes object may not contain embedded null bytes; if it does, the function returns `-1` and a `ValueError` is raised.

  The buffer refers to an internal buffer of obj, which includes an additional null byte at the end (not counted in length). The data must not be modified in any way, unless the object was just created using `PyBytes_FromStringAndSize(NULL, size)`. It must not be deallocated. If obj is not a bytes object at all, `PyBytes_AsStringAndSize()` returns `-1` and raises `TypeError`.

  Changed in version 3.5: Previously, `TypeError` was raised when embedded null bytes were encountered in the bytes object.

void `PyBytes_Concat`(PyObject **bytes, PyObject *newpart)

  Create a new bytes object in *bytes containing the contents of newpart appended to bytes; the caller will own the new reference. The reference to the old value of bytes will be stolen. If the new object cannot be created, the old reference to bytes will still be discarded and the value of *bytes will be set to NULL; the appropriate exception will be set.

void `PyBytes_ConcatAndDel`(PyObject **bytes, PyObject *newpart)

  Create a new bytes object in *bytes containing the contents of newpart appended to bytes. This version decrements the reference count of newpart.

int `_PyBytes_Resize`(PyObject **bytes, Py_ssize_t newsize)

  A way to resize a bytes object even though it is “immutable”. Only use this to build up a brand new bytes object; don’t use this if the bytes may already be known in other parts of the code. It is an error to call this function if the refcount on the input bytes object is not one. Pass the address of an existing bytes object as an lvalue (it may be written into), and the new size desired. On success, *bytes holds the resized bytes object and `0` is returned; the address in *bytes may differ from its input value. If the reallocation fails, the original bytes object at *bytes is deallocated, *bytes is set to NULL, `MemoryError` is set, and `-1` is returned.