:mod:`sys.monitoring` --- Execution event monitoring
====================================================
-.. module:: sys.monitoring
- :synopsis: Access and control event monitoring
+.. module:: sys.monitoring
+ :synopsis: Access and control event monitoring
+
+.. versionadded:: 3.12
-----------------
.. note::
- ``sys.monitoring`` is a namespace within the ``sys`` module,
+ :mod:`sys.monitoring` is a namespace within the :mod:`sys` module,
not an independent module, so there is no need to
``import sys.monitoring``, simply ``import sys`` and then use
``sys.monitoring``.
activate and control event monitoring.
As programs execute, events occur that might be of interest to tools that
-monitor execution. The :mod:`!sys.monitoring` namespace provides means to
+monitor execution. The :mod:`sys.monitoring` namespace provides means to
receive callbacks when events of interest occur.
The monitoring API consists of three components:
-* Tool identifiers
-* Events
-* Callbacks
+* `Tool identifiers`_
+* `Events`_
+* :ref:`Callbacks <callbacks>`
Tool identifiers
----------------
-A tool identifier is an integer and associated name.
+A tool identifier is an integer and the associated name.
Tool identifiers are used to discourage tools from interfering with each
other and to allow multiple tools to operate at the same time.
Currently tools are completely independent and cannot be used to
monitor each other. This restriction may be lifted in the future.
Before registering or activating events, a tool should choose an identifier.
-Identifiers are integers in the range 0 to 5.
+Identifiers are integers in the range 0 to 5 inclusive.
Registering and using tools
'''''''''''''''''''''''''''
.. function:: use_tool_id(id: int, name: str) -> None
- Must be called before ``id`` can be used.
- ``id`` must be in the range 0 to 5 inclusive.
- Raises a ``ValueError`` if ``id`` is in use.
+ Must be called before *id* can be used.
+ *id* must be in the range 0 to 5 inclusive.
+ Raises a :exc:`ValueError` if *id* is in use.
.. function:: free_tool_id(id: int) -> None
- Should be called once a tool no longer requires ``id``.
+ Should be called once a tool no longer requires *id*.
.. function:: get_tool(id: int) -> str | None
- Returns the name of the tool if ``id`` is in use,
+ Returns the name of the tool if *id* is in use,
otherwise it returns ``None``.
- ``id`` must be in the range 0 to 5 inclusive.
+ *id* must be in the range 0 to 5 inclusive.
All IDs are treated the same by the VM with regard to events, but the
following IDs are pre-defined to make co-operation of tools easier::
The following events are supported:
-BRANCH
- A conditional branch is taken (or not).
-CALL
- A call in Python code (event occurs before the call).
-C_RAISE
- Exception raised from any callable, except Python functions (event occurs after the exit).
-C_RETURN
- Return from any callable, except Python functions (event occurs after the return).
-EXCEPTION_HANDLED
- An exception is handled.
-INSTRUCTION
- A VM instruction is about to be executed.
-JUMP
- An unconditional jump in the control flow graph is made.
-LINE
- An instruction is about to be executed that has a different line number from the preceding instruction.
-PY_RESUME
- Resumption of a Python function (for generator and coroutine functions), except for throw() calls.
-PY_RETURN
- Return from a Python function (occurs immediately before the return, the callee's frame will be on the stack).
-PY_START
- Start of a Python function (occurs immediately after the call, the callee's frame will be on the stack)
-PY_THROW
- A Python function is resumed by a throw() call.
-PY_UNWIND
- Exit from a Python function during exception unwinding.
-PY_YIELD
- Yield from a Python function (occurs immediately before the yield, the callee's frame will be on the stack).
-RAISE
- An exception is raised, except those that cause a ``STOP_ITERATION`` event.
-RERAISE
- An exception is re-raised, for example at the end of a ``finally`` block.
-STOP_ITERATION
- An artificial ``StopIteration`` is raised; see `the STOP_ITERATION event`_.
+.. monitoring-event:: BRANCH
+
+ A conditional branch is taken (or not).
+
+.. monitoring-event:: CALL
+
+ A call in Python code (event occurs before the call).
+
+.. monitoring-event:: C_RAISE
+
+ An exception raised from any callable, except for Python functions (event occurs after the exit).
+
+.. monitoring-event:: C_RETURN
+
+ Return from any callable, except for Python functions (event occurs after the return).
+
+.. monitoring-event:: EXCEPTION_HANDLED
+
+ An exception is handled.
+
+.. monitoring-event:: INSTRUCTION
+
+ A VM instruction is about to be executed.
+
+.. monitoring-event:: JUMP
+
+ An unconditional jump in the control flow graph is made.
+
+.. monitoring-event:: LINE
+
+ An instruction is about to be executed that has a different line number from the preceding instruction.
+
+.. monitoring-event:: PY_RESUME
+
+ Resumption of a Python function (for generator and coroutine functions), except for ``throw()`` calls.
+
+.. monitoring-event:: PY_RETURN
+
+ Return from a Python function (occurs immediately before the return, the callee's frame will be on the stack).
+
+.. monitoring-event:: PY_START
+
+ Start of a Python function (occurs immediately after the call, the callee's frame will be on the stack)
+
+.. monitoring-event:: PY_THROW
+
+ A Python function is resumed by a ``throw()`` call.
+
+.. monitoring-event:: PY_UNWIND
+
+ Exit from a Python function during exception unwinding.
+
+.. monitoring-event:: PY_YIELD
+
+ Yield from a Python function (occurs immediately before the yield, the callee's frame will be on the stack).
+
+.. monitoring-event:: RAISE
+
+ An exception is raised, except those that cause a :monitoring-event:`STOP_ITERATION` event.
+
+.. monitoring-event:: RERAISE
+
+ An exception is re-raised, for example at the end of a :keyword:`finally` block.
+
+.. monitoring-event:: STOP_ITERATION
+
+ An artificial :exc:`StopIteration` is raised; see `the STOP_ITERATION event`_.
+
More events may be added in the future.
These events are attributes of the :mod:`!sys.monitoring.events` namespace.
Each event is represented as a power-of-2 integer constant.
To define a set of events, simply bitwise or the individual events together.
-For example, to specify both ``PY_RETURN`` and ``PY_START`` events, use the
-expression ``PY_RETURN | PY_START``.
+For example, to specify both :monitoring-event:`PY_RETURN` and :monitoring-event:`PY_START`
+events, use the expression ``PY_RETURN | PY_START``.
+
+.. monitoring-event:: NO_EVENTS
+
+ An alias for ``0`` so users can do explict comparisions like::
+
+ if get_events(DEBUGGER_ID) == NO_EVENTS:
+ ...
Events are divided into three groups:
at clearly defined locations. All local events can be disabled.
The local events are:
-* PY_START
-* PY_RESUME
-* PY_RETURN
-* PY_YIELD
-* CALL
-* LINE
-* INSTRUCTION
-* JUMP
-* BRANCH
-* STOP_ITERATION
+* :monitoring-event:`PY_START`
+* :monitoring-event:`PY_RESUME`
+* :monitoring-event:`PY_RETURN`
+* :monitoring-event:`PY_YIELD`
+* :monitoring-event:`CALL`
+* :monitoring-event:`LINE`
+* :monitoring-event:`INSTRUCTION`
+* :monitoring-event:`JUMP`
+* :monitoring-event:`BRANCH`
+* :monitoring-event:`STOP_ITERATION`
Ancillary events
''''''''''''''''
Ancillary events can be monitored like other events, but are controlled
by another event:
-* C_RAISE
-* C_RETURN
+* :monitoring-event:`C_RAISE`
+* :monitoring-event:`C_RETURN`
-The ``C_RETURN`` and ``C_RAISE`` events are controlled by the ``CALL``
-event. ``C_RETURN`` and ``C_RAISE`` events will only be seen if the
-corresponding ``CALL`` event is being monitored.
+The :monitoring-event:`C_RETURN` and :monitoring-event:`C_RAISE` events
+are controlled by the :monitoring-event:`CALL` event.
+:monitoring-event:`C_RETURN` and :monitoring-event:`C_RAISE` events will only be seen if the
+corresponding :monitoring-event:`CALL` event is being monitored.
Other events
''''''''''''
The other events that can be monitored are:
-* PY_THROW
-* PY_UNWIND
-* RAISE
-* EXCEPTION_HANDLED
+* :monitoring-event:`PY_THROW`
+* :monitoring-event:`PY_UNWIND`
+* :monitoring-event:`RAISE`
+* :monitoring-event:`EXCEPTION_HANDLED`
The STOP_ITERATION event
''''''''''''''''''''''''
:pep:`PEP 380 <380#use-of-stopiteration-to-return-values>`
-specifies that a ``StopIteration`` exception is raised when returning a value
+specifies that a :exc:`StopIteration` exception is raised when returning a value
from a generator or coroutine. However, this is a very inefficient way to
return a value, so some Python implementations, notably CPython 3.12+, do not
raise an exception unless it would be visible to other code.
To allow tools to monitor for real exceptions without slowing down generators
-and coroutines, the ``STOP_ITERATION`` event is provided.
-``STOP_ITERATION`` can be locally disabled, unlike ``RAISE``.
+and coroutines, the :monitoring-event:`STOP_ITERATION` event is provided.
+:monitoring-event:`STOP_ITERATION` can be locally disabled, unlike :monitoring-event:`RAISE`.
Turning events on and off
-------------------------
-In order to monitor an event, it must be turned on and a callback registered.
+In order to monitor an event, it must be turned on and a corresponding callback
+must be registered.
Events can be turned on or off by setting the events either globally or
for a particular code object.
.. function:: set_events(tool_id: int, event_set: int)
- Activates all events which are set in ``event_set``.
- Raises a ``ValueError`` if ``tool_id`` is not in use.
+ Activates all events which are set in *event_set*.
+ Raises a :exc:`ValueError` if *tool_id* is not in use.
No events are active by default.
.. function:: get_local_events(tool_id: int, code: CodeType) -> int
- Returns all the local events for ``code``
+ Returns all the local events for *code*
.. function:: set_local_events(tool_id: int, code: CodeType, event_set: int)
- Activates all the local events for ``code`` which are set in ``event_set``.
- Raises a ``ValueError`` if ``tool_id`` is not in use.
+ Activates all the local events for *code* which are set in *event_set*.
+ Raises a :exc:`ValueError` if *tool_id* is not in use.
Local events add to global events, but do not mask them.
In other words, all global events will trigger for a code object,
Disabling events
''''''''''''''''
+.. data:: DISABLE
+
+ A special value that can be returned from a callback function to disable
+ events for the current code location.
+
Local events can be disabled for a specific code location by returning
-``sys.monitoring.DISABLE`` from a callback function. This does not change
+:data:`sys.monitoring.DISABLE` from a callback function. This does not change
which events are set, or any other code locations for the same event.
Disabling events for specific locations is very important for high
except for a few breakpoints.
+.. _callbacks:
+
Registering callback functions
------------------------------
.. function:: register_callback(tool_id: int, event: int, func: Callable | None) -> Callable | None
- Registers the callable ``func`` for the ``event`` with the given ``tool_id``
+ Registers the callable *func* for the *event* with the given *tool_id*
- If another callback was registered for the given ``tool_id`` and ``event``,
+ If another callback was registered for the given *tool_id* and *event*,
it is unregistered and returned.
- Otherwise ``register_callback`` returns ``None``.
+ Otherwise :func:`register_callback` returns ``None``.
Functions can be unregistered by calling
Callback functions can be registered and unregistered at any time.
-Registering or unregistering a callback function will generate a ``sys.audit`` event.
+Registering or unregistering a callback function will generate a :func:`sys.audit` event.
Callback function arguments
'''''''''''''''''''''''''''
+.. data:: MISSING
+
+ A special value that is passed to a callback function to indicate
+ that there are no arguments to the call.
+
When an active event occurs, the registered callback function is called.
Different events will provide the callback function with different arguments, as follows:
-* ``PY_START`` and ``PY_RESUME``::
+* :monitoring-event:`PY_START` and :monitoring-event:`PY_RESUME`::
func(code: CodeType, instruction_offset: int) -> DISABLE | Any
-* ``PY_RETURN`` and ``PY_YIELD``:
+* :monitoring-event:`PY_RETURN` and :monitoring-event:`PY_YIELD`::
- ``func(code: CodeType, instruction_offset: int, retval: object) -> DISABLE | Any``
+ func(code: CodeType, instruction_offset: int, retval: object) -> DISABLE | Any
-* ``CALL``, ``C_RAISE`` and ``C_RETURN``:
+* :monitoring-event:`CALL`, :monitoring-event:`C_RAISE` and :monitoring-event:`C_RETURN`::
- ``func(code: CodeType, instruction_offset: int, callable: object, arg0: object | MISSING) -> DISABLE | Any``
+ func(code: CodeType, instruction_offset: int, callable: object, arg0: object | MISSING) -> DISABLE | Any
- If there are no arguments, ``arg0`` is set to ``MISSING``.
+ If there are no arguments, *arg0* is set to :data:`sys.monitoring.MISSING`.
-* ``RAISE``, ``RERAISE``, ``EXCEPTION_HANDLED``, ``PY_UNWIND``, ``PY_THROW`` and ``STOP_ITERATION``:
+* :monitoring-event:`RAISE`, :monitoring-event:`RERAISE`, :monitoring-event:`EXCEPTION_HANDLED`,
+ :monitoring-event:`PY_UNWIND`, :monitoring-event:`PY_THROW` and :monitoring-event:`STOP_ITERATION`::
- ``func(code: CodeType, instruction_offset: int, exception: BaseException) -> DISABLE | Any``
+ func(code: CodeType, instruction_offset: int, exception: BaseException) -> DISABLE | Any
-* ``LINE``:
+* :monitoring-event:`LINE`::
- ``func(code: CodeType, line_number: int) -> DISABLE | Any``
+ func(code: CodeType, line_number: int) -> DISABLE | Any
-* ``BRANCH`` and ``JUMP``:
+* :monitoring-event:`BRANCH` and :monitoring-event:`JUMP`::
- ``func(code: CodeType, instruction_offset: int, destination_offset: int) -> DISABLE | Any``
+ func(code: CodeType, instruction_offset: int, destination_offset: int) -> DISABLE | Any
- Note that the ``destination_offset`` is where the code will next execute.
+ Note that the *destination_offset* is where the code will next execute.
For an untaken branch this will be the offset of the instruction following
the branch.
-* ``INSTRUCTION``:
-
- ``func(code: CodeType, instruction_offset: int) -> DISABLE | Any``
-
+* :monitoring-event:`INSTRUCTION`::
+ func(code: CodeType, instruction_offset: int) -> DISABLE | Any
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