C API and ABI Stability¶
Unless documented otherwise, Python's C API is covered by the Backwards Compatibility Policy, PEP 387. Most changes to it are source-compatible (typically by only adding new API). Changing existing API or removing API is only done after a deprecation period or to fix serious issues.
CPython's Application Binary Interface (ABI) is forward- and backwards-compatible across a minor release (if these are compiled the same way; see Pertimbangan Platform below). So, code compiled for Python 3.10.0 will work on 3.10.8 and vice versa, but will need to be compiled separately for 3.9.x and 3.11.x.
There are two tiers of C API with different stability expectations:
Unstable API, may change in minor versions without a deprecation period. It is marked by the
PyUnstable
prefix in names.Limited API, is compatible across several minor releases. When
Py_LIMITED_API
is defined, only this subset is exposed fromPython.h
.
Hal ini dibahas secara lebih rinci di bawah ini.
Names prefixed by an underscore, such as _Py_InternalState
,
are private API that can change without notice even in patch releases.
If you need to use this API, consider reaching out to
CPython developers
to discuss adding public API for your use case.
API C yang tidak stabil¶
Any API named with the PyUnstable
prefix exposes CPython implementation
details, and may change in every minor release (e.g. from 3.9 to 3.10) without
any deprecation warnings.
However, it will not change in a bugfix release (e.g. from 3.10.0 to 3.10.1).
It is generally intended for specialized, low-level tools like debuggers.
Projects that use this API are expected to follow CPython development and spend extra effort adjusting to changes.
Stable Application Binary Interface¶
For simplicity, this document talks about extensions, but the Limited API and Stable ABI work the same way for all uses of the API – for example, embedding Python.
API C terbatas¶
Python 3.2 introduced the Limited API, a subset of Python's C API. Extensions that only use the Limited API can be compiled once and be loaded on multiple versions of Python. Contents of the Limited API are listed below.
-
Py_LIMITED_API¶
Define this macro before including
Python.h
to opt in to only use the Limited API, and to select the Limited API version.Define
Py_LIMITED_API
to the value ofPY_VERSION_HEX
corresponding to the lowest Python version your extension supports. The extension will be ABI-compatible with all Python 3 releases from the specified one onward, and can use Limited API introduced up to that version.Rather than using the
PY_VERSION_HEX
macro directly, hardcode a minimum minor version (e.g.0x030A0000
for Python 3.10) for stability when compiling with future Python versions.You can also define
Py_LIMITED_API
to3
. This works the same as0x03020000
(Python 3.2, the version that introduced Limited API).
Stable ABI¶
To enable this, Python provides a Stable ABI: a set of symbols that will remain ABI-compatible across Python 3.x versions.
Catatan
The Stable ABI prevents ABI issues, like linker errors due to missing symbols or data corruption due to changes in structure layouts or function signatures. However, other changes in Python can change the behavior of extensions. See Python's Backwards Compatibility Policy (PEP 387) for details.
The Stable ABI contains symbols exposed in the Limited API, but also other ones – for example, functions necessary to support older versions of the Limited API.
On Windows, extensions that use the Stable ABI should be linked against
python3.dll
rather than a version-specific library such as
python39.dll
.
On some platforms, Python will look for and load shared library files named
with the abi3
tag (e.g. mymodule.abi3.so
).
It does not check if such extensions conform to a Stable ABI.
The user (or their packaging tools) need to ensure that, for example,
extensions built with the 3.10+ Limited API are not installed for lower
versions of Python.
All functions in the Stable ABI are present as functions in Python's shared library, not solely as macros. This makes them usable from languages that don't use the C preprocessor.
Cakupan dan Kinerja API Terbatas¶
The goal for the Limited API is to allow everything that is possible with the full C API, but possibly with a performance penalty.
For example, while PyList_GetItem()
is available, its “unsafe” macro
variant PyList_GET_ITEM()
is not.
The macro can be faster because it can rely on version-specific implementation
details of the list object.
Without Py_LIMITED_API
defined, some C API functions are inlined or
replaced by macros.
Defining Py_LIMITED_API
disables this inlining, allowing stability as
Python's data structures are improved, but possibly reducing performance.
By leaving out the Py_LIMITED_API
definition, it is possible to compile
a Limited API extension with a version-specific ABI. This can improve
performance for that Python version, but will limit compatibility.
Compiling with Py_LIMITED_API
will then yield an extension that can be
distributed where a version-specific one is not available – for example,
for prereleases of an upcoming Python version.
Peringatan API Terbatas¶
Note that compiling with Py_LIMITED_API
is not a complete guarantee that
code conforms to the Limited API or the Stable ABI. Py_LIMITED_API
only covers definitions, but an API also
includes other issues, such as expected semantics.
One issue that Py_LIMITED_API
does not guard against is calling a function
with arguments that are invalid in a lower Python version.
For example, consider a function that starts accepting NULL
for an
argument. In Python 3.9, NULL
now selects a default behavior, but in
Python 3.8, the argument will be used directly, causing a NULL
dereference
and crash. A similar argument works for fields of structs.
Another issue is that some struct fields are currently not hidden when
Py_LIMITED_API
is defined, even though they're part of the Limited API.
For these reasons, we recommend testing an extension with all minor Python versions it supports, and preferably to build with the lowest such version.
We also recommend reviewing documentation of all used API to check
if it is explicitly part of the Limited API. Even with Py_LIMITED_API
defined, a few private declarations are exposed for technical reasons (or
even unintentionally, as bugs).
Also note that the Limited API is not necessarily stable: compiling with
Py_LIMITED_API
with Python 3.8 means that the extension will
run with Python 3.12, but it will not necessarily compile with Python 3.12.
In particular, parts of the Limited API may be deprecated and removed,
provided that the Stable ABI stays stable.
Pertimbangan Platform¶
ABI stability depends not only on Python, but also on the compiler used, lower-level libraries and compiler options. For the purposes of the Stable ABI, these details define a “platform”. They usually depend on the OS type and processor architecture
It is the responsibility of each particular distributor of Python
to ensure that all Python versions on a particular platform are built
in a way that does not break the Stable ABI.
This is the case with Windows and macOS releases from python.org
and many
third-party distributors.
ABI Checking¶
Added in version 3.15.0a0 (unreleased).
Python includes a rudimentary check for ABI compatibility.
This check is not comprehensive. It only guards against common cases of incompatible modules being installed for the wrong interpreter. It also does not take platform incompatibilities into account. It can only be done after an extension is successfully loaded.
Despite these limitations, it is recommended that extension modules use this mechanism, so that detectable incompatibilities raise exceptions rather than crash.
Most modules can use this check via the Py_mod_abi
slot and the PyABIInfo_VAR
macro, for example like this:
PyABIInfo_VAR(abi_info);
static PyModuleDef_Slot mymodule_slots[] = {
{Py_mod_abi, &abi_info},
...
};
The full API is described below for advanced use cases.
-
int PyABIInfo_Check(PyABIInfo *info, const char *module_name)¶
- Part of the Stable ABI since version 3.15.
Verify that the given info is compatible with the currently running interpreter.
Return 0 on success. On failure, raise an exception and return -1.
If the ABI is incompatible, the raised exception will be
ImportError
.The module_name argument can be
NULL
, or point to a NUL-terminated UTF-8-encoded string used for error messages.Note that if info describes the ABI that the current code uses (as defined by
PyABIInfo_VAR
, for example), using any other Python C API may lead to crashes. In particular, it is not safe to examine the raised exception.Added in version 3.15.0a0 (unreleased).
-
PyABIInfo_VAR(NAME)¶
- Part of the Stable ABI since version 3.15.
Define a static
PyABIInfo
variable with the given NAME that describes the ABI that the current code will use. This macro expands to:static PyABIInfo NAME = { 1, 0, PyABIInfo_DEFAULT_FLAGS, PY_VERSION_HEX, PyABIInfo_DEFAULT_ABI_VERSION }
Added in version 3.15.0a0 (unreleased).
-
type PyABIInfo¶
- Part of the Stable ABI (including all members) since version 3.15.
-
uint8_t abiinfo_major_version¶
The major version of
PyABIInfo
. Can be set to:0
to skip all checking, or1
to specify this version ofPyABIInfo
.
-
uint8_t abiinfo_minor_version¶
The major version of
PyABIInfo
. Must be set to0
; larger values are reserved for backwards-compatible future versions ofPyABIInfo
.
-
uint16_t flags¶
This field is usually set to the following macro:
-
PyABIInfo_DEFAULT_FLAGS¶
Default flags, based on current values of macros such as
Py_LIMITED_API
andPy_GIL_DISABLED
.
Alternately, the field can be set to to the following flags, combined by bitwise OR. Unused bits must be set to zero.
ABI variant -- one of:
Free-threading compatibility -- one of:
-
PyABIInfo_FREETHREADED¶
Specifies ABI compatible with free-threading builds of CPython. (That is, ones compiled with
--disable-gil
; witht
insys.abiflags
)
-
PyABIInfo_GIL¶
Specifies ABI compatible with non-free-threading builds of CPython (ones compiled without
--disable-gil
).
-
PyABIInfo_DEFAULT_FLAGS¶
-
uint32_t build_version¶
The version of the Python headers used to build the code, in the format used by
PY_VERSION_HEX
.This can be set to
0
to skip any checks related to this field. This option is meant mainly for projects that do not use the CPython headers directly, and do not emulate a specific version of them.
-
uint32_t abi_version¶
The ABI version.
For the Stable ABI, this field should be the value of
Py_LIMITED_API
(except ifPy_LIMITED_API
is3
; use Py_PACK_VERSION(3, 2) in that case).Otherwise, it should be set to
PY_VERSION_HEX
.It can also be set to
0
to skip any checks related to this field.-
PyABIInfo_DEFAULT_ABI_VERSION¶
The value that should be used for this field, based on current values of macros such as
Py_LIMITED_API
,PY_VERSION_HEX
andPy_GIL_DISABLED
.
-
PyABIInfo_DEFAULT_ABI_VERSION¶
Added in version 3.15.0a0 (unreleased).
-
uint8_t abiinfo_major_version¶
Konten dari API Terbatas¶
Currently, the Limited API includes the following items:
PyByteArrayIter_Type
PyBytesIter_Type
PyBytes_DecodeEscape()
PyBytes_Repr()
PyCFunction_GetFlags()
PyCFunction_GetFunction()
PyCFunction_GetSelf()
PyCFunction_Type
PyCapsule_Type
PyClassMethodDescr_Type
PyDictItems_Type
PyDictIterItem_Type
PyDictIterKey_Type
PyDictIterValue_Type
PyDictKeys_Type
PyDictProxy_Type
PyDictRevIterItem_Type
PyDictRevIterKey_Type
PyDictRevIterValue_Type
PyDictValues_Type
PyEnum_Type
PyErr_Display()
PyErr_ProgramText()
PyFilter_Type
PyGILState_STATE
PyGetSetDescr_Type
PyListIter_Type
PyListRevIter_Type
PyLongRangeIter_Type
PyMap_Type
PyMemberDescr_Type
PyMemoryView_Type
PyMethodDescr_Type
PyModuleDef_Base
PyModuleDef_Type
PyOS_InterruptOccurred()
PyOS_mystricmp()
PyOS_mystrnicmp()
PyRangeIter_Type
PyRange_Type
PyReversed_Type
PySetIter_Type
PySuper_Type
PyThread_GetInfo()
PyThread_acquire_lock()
PyThread_acquire_lock_timed()
PyThread_allocate_lock()
PyThread_exit_thread()
PyThread_free_lock()
PyThread_get_stacksize()
PyThread_get_thread_ident()
PyThread_get_thread_native_id()
PyThread_init_thread()
PyThread_release_lock()
PyThread_set_stacksize()
PyThread_start_new_thread()
PyTraceBack_Here()
PyTraceBack_Print()
PyTraceBack_Type
PyTupleIter_Type
PyVarObject.ob_base
PyWeakReference
PyWrapperDescr_Type
PyZip_Type
Py_FileSystemDefaultEncodeErrors
Py_FileSystemDefaultEncoding
Py_GetRecursionLimit()
Py_HasFileSystemDefaultEncoding
Py_MakePendingCalls()
Py_SetRecursionLimit()
Py_UTF8Mode
Py_intptr_t
Py_uintptr_t
ssizessizeargfunc
ssizessizeobjargproc
symtable