Code Objects

Code objects are a low-level detail of the CPython implementation. Each one represents a chunk of executable code that hasn’t yet been bound into a function.

type PyCodeObject

The C structure of the objects used to describe code objects. The fields of this type are subject to change at any time.

PyTypeObject PyCode_Type

This is an instance of PyTypeObject representing the Python code object.

int PyCode_Check(PyObject *co)

Return true if co is a code object. This function always succeeds.

Py_ssize_t PyCode_GetNumFree(PyCodeObject *co)

Return the number of free (closure) variables in a code object.

int PyUnstable_Code_GetFirstFree(PyCodeObject *co)

This is Unstable API. It may change without warning in minor releases.

Return the position of the first free (closure) variable in a code object.

Changed in version 3.13: Renamed from PyCode_GetFirstFree as part of Unstable C API. The old name is deprecated, but will remain available until the signature changes again.

PyCodeObject *PyUnstable_Code_New(int argcount, int kwonlyargcount, int nlocals, int stacksize, int flags, PyObject *code, PyObject *consts, PyObject *names, PyObject *varnames, PyObject *freevars, PyObject *cellvars, PyObject *filename, PyObject *name, PyObject *qualname, int firstlineno, PyObject *linetable, PyObject *exceptiontable)

This is Unstable API. It may change without warning in minor releases.

Return a new code object. If you need a dummy code object to create a frame, use PyCode_NewEmpty() instead.

Since the definition of the bytecode changes often, calling PyUnstable_Code_New() directly can bind you to a precise Python version.

The many arguments of this function are inter-dependent in complex ways, meaning that subtle changes to values are likely to result in incorrect execution or VM crashes. Use this function only with extreme care.

Changed in version 3.11: Added qualname and exceptiontable parameters.

Changed in version 3.12: Renamed from PyCode_New as part of Unstable C API. The old name is deprecated, but will remain available until the signature changes again.

PyCodeObject *PyUnstable_Code_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount, int nlocals, int stacksize, int flags, PyObject *code, PyObject *consts, PyObject *names, PyObject *varnames, PyObject *freevars, PyObject *cellvars, PyObject *filename, PyObject *name, PyObject *qualname, int firstlineno, PyObject *linetable, PyObject *exceptiontable)

This is Unstable API. It may change without warning in minor releases.

Similar to PyUnstable_Code_New(), but with an extra “posonlyargcount” for positional-only arguments. The same caveats that apply to PyUnstable_Code_New also apply to this function.

Added in version 3.8: as PyCode_NewWithPosOnlyArgs

Changed in version 3.11: Added qualname and exceptiontable parameters.

Changed in version 3.12: Renamed to PyUnstable_Code_NewWithPosOnlyArgs. The old name is deprecated, but will remain available until the signature changes again.

PyCodeObject *PyCode_NewEmpty(const char *filename, const char *funcname, int firstlineno)

Return value: New reference.

Return a new empty code object with the specified filename, function name, and first line number. The resulting code object will raise an Exception if executed.

int PyCode_Addr2Line(PyCodeObject *co, int byte_offset)

Return the line number of the instruction that occurs on or before byte_offset and ends after it. If you just need the line number of a frame, use PyFrame_GetLineNumber() instead.

For efficiently iterating over the line numbers in a code object, use the API described in PEP 626.

int PyCode_Addr2Location(PyObject *co, int byte_offset, int *start_line, int *start_column, int *end_line, int *end_column)

Sets the passed int pointers to the source code line and column numbers for the instruction at byte_offset. Sets the value to 0 when information is not available for any particular element.

Returns 1 if the function succeeds and 0 otherwise.

Added in version 3.11.

PyObject *PyCode_GetCode(PyCodeObject *co)

Equivalent to the Python code getattr(co, 'co_code'). Returns a strong reference to a PyBytesObject representing the bytecode in a code object. On error, NULL is returned and an exception is raised.

This PyBytesObject may be created on-demand by the interpreter and does not necessarily represent the bytecode actually executed by CPython. The primary use case for this function is debuggers and profilers.

Added in version 3.11.

PyObject *PyCode_GetVarnames(PyCodeObject *co)

Equivalent to the Python code getattr(co, 'co_varnames'). Returns a new reference to a PyTupleObject containing the names of the local variables. On error, NULL is returned and an exception is raised.

Added in version 3.11.

PyObject *PyCode_GetCellvars(PyCodeObject *co)

Equivalent to the Python code getattr(co, 'co_cellvars'). Returns a new reference to a PyTupleObject containing the names of the local variables that are referenced by nested functions. On error, NULL is returned and an exception is raised.

Added in version 3.11.

PyObject *PyCode_GetFreevars(PyCodeObject *co)

Equivalent to the Python code getattr(co, 'co_freevars'). Returns a new reference to a PyTupleObject containing the names of the free (closure) variables. On error, NULL is returned and an exception is raised.

Added in version 3.11.

int PyCode_AddWatcher(PyCode_WatchCallback callback)

Register callback as a code object watcher for the current interpreter. Return an ID which may be passed to PyCode_ClearWatcher(). In case of error (e.g. no more watcher IDs available), return -1 and set an exception.

Added in version 3.12.

int PyCode_ClearWatcher(int watcher_id)

Clear watcher identified by watcher_id previously returned from PyCode_AddWatcher() for the current interpreter. Return 0 on success, or -1 and set an exception on error (e.g. if the given watcher_id was never registered.)

Added in version 3.12.

type PyCodeEvent

Enumeration of possible code object watcher events: - PY_CODE_EVENT_CREATE - PY_CODE_EVENT_DESTROY

Added in version 3.12.

typedef int (*PyCode_WatchCallback)(PyCodeEvent event, PyCodeObject *co)

Type of a code object watcher callback function.

If event is PY_CODE_EVENT_CREATE, then the callback is invoked after co has been fully initialized. Otherwise, the callback is invoked before the destruction of co takes place, so the prior state of co can be inspected.

If event is PY_CODE_EVENT_DESTROY, taking a reference in the callback to the about-to-be-destroyed code object will resurrect it and prevent it from being freed at this time. When the resurrected object is destroyed later, any watcher callbacks active at that time will be called again.

Users of this API should not rely on internal runtime implementation details. Such details may include, but are not limited to, the exact order and timing of creation and destruction of code objects. While changes in these details may result in differences observable by watchers (including whether a callback is invoked or not), it does not change the semantics of the Python code being executed.

If the callback sets an exception, it must return -1; this exception will be printed as an unraisable exception using PyErr_WriteUnraisable(). Otherwise it should return 0.

There may already be a pending exception set on entry to the callback. In this case, the callback should return 0 with the same exception still set. This means the callback may not call any other API that can set an exception unless it saves and clears the exception state first, and restores it before returning.

Added in version 3.12.

Extra information

To support low-level extensions to frame evaluation, such as external just-in-time compilers, it is possible to attach arbitrary extra data to code objects.

These functions are part of the unstable C API tier: this functionality is a CPython implementation detail, and the API may change without deprecation warnings.

Py_ssize_t PyUnstable_Eval_RequestCodeExtraIndex(freefunc free)

This is Unstable API. It may change without warning in minor releases.

Return a new an opaque index value used to adding data to code objects.

You generally call this function once (per interpreter) and use the result with PyCode_GetExtra and PyCode_SetExtra to manipulate data on individual code objects.

If free is not NULL: when a code object is deallocated, free will be called on non-NULL data stored under the new index. Use Py_DecRef() when storing PyObject.

Added in version 3.6: as _PyEval_RequestCodeExtraIndex

Changed in version 3.12: Renamed to PyUnstable_Eval_RequestCodeExtraIndex. The old private name is deprecated, but will be available until the API changes.

int PyUnstable_Code_GetExtra(PyObject *code, Py_ssize_t index, void **extra)

This is Unstable API. It may change without warning in minor releases.

Set extra to the extra data stored under the given index. Return 0 on success. Set an exception and return -1 on failure.

If no data was set under the index, set extra to NULL and return 0 without setting an exception.

Added in version 3.6: as _PyCode_GetExtra

Changed in version 3.12: Renamed to PyUnstable_Code_GetExtra. The old private name is deprecated, but will be available until the API changes.

int PyUnstable_Code_SetExtra(PyObject *code, Py_ssize_t index, void *extra)

This is Unstable API. It may change without warning in minor releases.

Set the extra data stored under the given index to extra. Return 0 on success. Set an exception and return -1 on failure.

Added in version 3.6: as _PyCode_SetExtra

Changed in version 3.12: Renamed to PyUnstable_Code_SetExtra. The old private name is deprecated, but will be available until the API changes.