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:mod:`!dis` --- Disassembler for Python bytecode
================================================
.. module:: dis
:synopsis: Disassembler for Python bytecode.
**Source code:** :source:`Lib/dis.py`
.. testsetup::
import dis
def myfunc(alist):
return len(alist)
--------------
The :mod:`!dis` module supports the analysis of CPython :term:`bytecode` by
disassembling it. The CPython bytecode which this module takes as an input is
defined in the file :file:`Include/opcode.h` and used by the compiler and the
interpreter.
.. impl-detail::
Bytecode is an implementation detail of the CPython interpreter. No
guarantees are made that bytecode will not be added, removed, or changed
between versions of Python. Use of this module should not be considered to
work across Python VMs or Python releases.
.. versionchanged:: 3.6
Use 2 bytes for each instruction. Previously the number of bytes varied
by instruction.
.. versionchanged:: 3.10
The argument of jump, exception handling and loop instructions is now
the instruction offset rather than the byte offset.
.. versionchanged:: 3.11
Some instructions are accompanied by one or more inline cache entries,
which take the form of :opcode:`CACHE` instructions. These instructions
are hidden by default, but can be shown by passing ``show_caches=True`` to
any :mod:`!dis` utility. Furthermore, the interpreter now adapts the
bytecode to specialize it for different runtime conditions. The
adaptive bytecode can be shown by passing ``adaptive=True``.
.. versionchanged:: 3.12
The argument of a jump is the offset of the target instruction relative
to the instruction that appears immediately after the jump instruction's
:opcode:`CACHE` entries.
As a consequence, the presence of the :opcode:`CACHE` instructions is
transparent for forward jumps but needs to be taken into account when
reasoning about backward jumps.
.. versionchanged:: 3.13
The output shows logical labels rather than instruction offsets
for jump targets and exception handlers. The ``-O`` command line
option and the ``show_offsets`` argument were added.
.. versionchanged:: 3.14
The :option:`-P <dis --show-positions>` command-line option
and the ``show_positions`` argument were added.
The :option:`-S <dis --specialized>` command-line option is added.
Example: Given the function :func:`!myfunc`::
def myfunc(alist):
return len(alist)
the following command can be used to display the disassembly of
:func:`!myfunc`:
.. doctest::
>>> dis.dis(myfunc)
2 RESUME 0
<BLANKLINE>
3 LOAD_GLOBAL 1 (len + NULL)
LOAD_FAST_BORROW 0 (alist)
CALL 1
RETURN_VALUE
(The "2" is a line number).
.. _dis-cli:
Command-line interface
----------------------
The :mod:`!dis` module can be invoked as a script from the command line:
.. code-block:: sh
python -m dis [-h] [-C] [-O] [-P] [-S] [infile]
The following options are accepted:
.. program:: dis
.. option:: -h, --help
Display usage and exit.
.. option:: -C, --show-caches
Show inline caches.
.. versionadded:: 3.13
.. option:: -O, --show-offsets
Show offsets of instructions.
.. versionadded:: 3.13
.. option:: -P, --show-positions
Show positions of instructions in the source code.
.. versionadded:: 3.14
.. option:: -S, --specialized
Show specialized bytecode.
.. versionadded:: 3.14
If :file:`infile` is specified, its disassembled code will be written to stdout.
Otherwise, disassembly is performed on compiled source code received from stdin.
Bytecode analysis
-----------------
.. versionadded:: 3.4
The bytecode analysis API allows pieces of Python code to be wrapped in a
:class:`Bytecode` object that provides easy access to details of the compiled
code.
.. class:: Bytecode(x, *, first_line=None, current_offset=None,\
show_caches=False, adaptive=False, show_offsets=False,\
show_positions=False, show_jit=False)
Analyse the bytecode corresponding to a function, generator, asynchronous
generator, coroutine, method, string of source code, or a code object (as
returned by :func:`compile`).
This is a convenience wrapper around many of the functions listed below, most
notably :func:`get_instructions`, as iterating over a :class:`Bytecode`
instance yields the bytecode operations as :class:`Instruction` instances.
If *first_line* is not ``None``, it indicates the line number that should be
reported for the first source line in the disassembled code. Otherwise, the
source line information (if any) is taken directly from the disassembled code
object.
If *current_offset* is not ``None``, it refers to an instruction offset in the
disassembled code. Setting this means :meth:`.dis` will display a "current
instruction" marker against the specified opcode.
If *show_caches* is ``True``, :meth:`.dis` will display inline cache
entries used by the interpreter to specialize the bytecode.
If *adaptive* is ``True``, :meth:`.dis` will display specialized bytecode
that may be different from the original bytecode.
If *show_offsets* is ``True``, :meth:`.dis` will include instruction
offsets in the output.
If *show_positions* is ``True``, :meth:`.dis` will include instruction
source code positions in the output.
If *show_jit* is ``True``, :meth:`.dis` will show ``ENTER_EXECUTOR``
instructions, which mark JIT entry points and are hidden by default.
.. classmethod:: from_traceback(tb, *, show_caches=False)
Construct a :class:`Bytecode` instance from the given traceback, setting
*current_offset* to the instruction responsible for the exception.
.. data:: codeobj
The compiled code object.
.. data:: first_line
The first source line of the code object (if available)
.. method:: dis()
Return a formatted view of the bytecode operations (the same as printed by
:func:`dis.dis`, but returned as a multi-line string).
.. method:: info()
Return a formatted multi-line string with detailed information about the
code object, like :func:`code_info`.
.. versionchanged:: 3.7
This can now handle coroutine and asynchronous generator objects.
.. versionchanged:: 3.11
Added the *show_caches* and *adaptive* parameters.
.. versionchanged:: 3.13
Added the *show_offsets* parameter
.. versionchanged:: 3.14
Added the *show_positions* parameter.
.. versionchanged:: 3.16
Added the *show_jit* parameter.
Example:
.. doctest::
>>> bytecode = dis.Bytecode(myfunc)
>>> for instr in bytecode:
... print(instr.opname)
...
RESUME
LOAD_GLOBAL
LOAD_FAST_BORROW
CALL
RETURN_VALUE
Analysis functions
------------------
The :mod:`!dis` module also defines the following analysis functions that convert
the input directly to the desired output. They can be useful if only a single
operation is being performed, so the intermediate analysis object isn't useful:
.. function:: code_info(x)
Return a formatted multi-line string with detailed code object information
for the supplied function, generator, asynchronous generator, coroutine,
method, source code string or code object.
Note that the exact contents of code info strings are highly implementation
dependent and they may change arbitrarily across Python VMs or Python
releases.
.. versionadded:: 3.2
.. versionchanged:: 3.7
This can now handle coroutine and asynchronous generator objects.
.. function:: show_code(x, *, file=None)
Print detailed code object information for the supplied function, method,
source code string or code object to *file* (or ``sys.stdout`` if *file*
is not specified).
This is a convenient shorthand for ``print(code_info(x), file=file)``,
intended for interactive exploration at the interpreter prompt.
.. versionadded:: 3.2
.. versionchanged:: 3.4
Added *file* parameter.
.. function:: dis(x=None, *, file=None, depth=None, show_caches=False,\
adaptive=False, show_offsets=False, show_positions=False,\
show_jit=False)
Disassemble the *x* object. *x* can denote either a module, a class, a
method, a function, a generator, an asynchronous generator, a coroutine,
a code object, a string of source code or a byte sequence of raw bytecode.
For a module, it disassembles all functions. For a class, it disassembles
all methods (including class and static methods). For a code object or
sequence of raw bytecode, it prints one line per bytecode instruction.
It also recursively disassembles nested code objects. These can include
generator expressions, nested functions, the bodies of nested classes,
and the code objects used for :ref:`annotation scopes <annotation-scopes>`.
Strings are first compiled to code objects with the :func:`compile`
built-in function before being disassembled. If no object is provided, this
function disassembles the last traceback.
The disassembly is written as text to the supplied *file* argument if
provided and to ``sys.stdout`` otherwise.
The maximal depth of recursion is limited by *depth* unless it is ``None``.
``depth=0`` means no recursion.
If *show_caches* is ``True``, this function will display inline cache
entries used by the interpreter to specialize the bytecode.
If *adaptive* is ``True``, this function will display specialized bytecode
that may be different from the original bytecode.
If *show_jit* is ``True``, this function will show ``ENTER_EXECUTOR``
instructions, which mark JIT entry points and are hidden by default.
.. versionchanged:: 3.4
Added *file* parameter.
.. versionchanged:: 3.7
Implemented recursive disassembling and added *depth* parameter.
.. versionchanged:: 3.7
This can now handle coroutine and asynchronous generator objects.
.. versionchanged:: 3.11
Added the *show_caches* and *adaptive* parameters.
.. versionchanged:: 3.13
Added the *show_offsets* parameter.
.. versionchanged:: 3.14
Added the *show_positions* parameter.
.. versionchanged:: 3.16
Added the *show_jit* parameter.
.. function:: distb(tb=None, *, file=None, show_caches=False, adaptive=False,\
show_offsets=False, show_positions=False, show_jit=False)
Disassemble the top-of-stack function of a traceback, using the last
traceback if none was passed. The instruction causing the exception is
indicated.
The disassembly is written as text to the supplied *file* argument if
provided and to ``sys.stdout`` otherwise.
.. versionchanged:: 3.4
Added *file* parameter.
.. versionchanged:: 3.11
Added the *show_caches* and *adaptive* parameters.
.. versionchanged:: 3.13
Added the *show_offsets* parameter.
.. versionchanged:: 3.14
Added the *show_positions* parameter.
.. versionchanged:: 3.16
Added the *show_jit* parameter.
.. function:: disassemble(code, lasti=-1, *, file=None, show_caches=False,\
adaptive=False, show_offsets=False, show_positions=False,\
show_jit=False)
disco(code, lasti=-1, *, file=None, show_caches=False, adaptive=False,\
show_offsets=False, show_positions=False, show_jit=False)
Disassemble a code object, indicating the last instruction if *lasti* was
provided. The output is divided in the following columns:
#. the source code location of the instruction. Complete location information
is shown if *show_positions* is true. Otherwise (the default) only the
line number is displayed.
#. the current instruction, indicated as ``-->``,
#. a labelled instruction, indicated with ``>>``,
#. the address of the instruction,
#. the operation code name,
#. operation parameters, and
#. interpretation of the parameters in parentheses.
The parameter interpretation recognizes local and global variable names,
constant values, branch targets, and compare operators.
The disassembly is written as text to the supplied *file* argument if
provided and to ``sys.stdout`` otherwise.
.. versionchanged:: 3.4
Added *file* parameter.
.. versionchanged:: 3.11
Added the *show_caches* and *adaptive* parameters.
.. versionchanged:: 3.13
Added the *show_offsets* parameter.
.. versionchanged:: 3.14
Added the *show_positions* parameter.
.. versionchanged:: 3.16
Added the *show_jit* parameter.
.. function:: get_instructions(x, *, first_line=None, show_caches=False, adaptive=False, show_jit=False)
Return an iterator over the instructions in the supplied function, method,
source code string or code object.
The iterator generates a series of :class:`Instruction` named tuples giving
the details of each operation in the supplied code.
If *first_line* is not ``None``, it indicates the line number that should be
reported for the first source line in the disassembled code. Otherwise, the
source line information (if any) is taken directly from the disassembled code
object.
The *adaptive* parameter works as it does in :func:`dis`.
The *show_jit* parameter works as it does in :func:`dis`.
.. versionadded:: 3.4
.. versionchanged:: 3.11
Added the *show_caches* and *adaptive* parameters.
.. versionchanged:: 3.13
The *show_caches* parameter is deprecated and has no effect. The iterator
generates the :class:`Instruction` instances with the *cache_info*
field populated (regardless of the value of *show_caches*) and it no longer
generates separate items for the cache entries.
.. versionchanged:: 3.16
Added the *show_jit* parameter.
.. function:: findlinestarts(code)
This generator function uses the :meth:`~codeobject.co_lines` method
of the :ref:`code object <code-objects>` *code* to find the offsets which
are starts of
lines in the source code. They are generated as ``(offset, lineno)`` pairs.
.. versionchanged:: 3.6
Line numbers can be decreasing. Before, they were always increasing.
.. versionchanged:: 3.10
The :pep:`626` :meth:`~codeobject.co_lines` method is used instead of the
:attr:`~codeobject.co_firstlineno` and :attr:`!codeobject.co_lnotab`
attributes of the :ref:`code object <code-objects>`.
.. versionchanged:: 3.13
Line numbers can be ``None`` for bytecode that does not map to source lines.
.. function:: findlabels(code)
Detect all offsets in the raw compiled bytecode string *code* which are jump targets, and
return a list of these offsets.
.. function:: stack_effect(opcode, oparg=None, *, jump=None)
Compute the stack effect of *opcode* with argument *oparg*.
If the code has a jump target and *jump* is ``True``, :func:`~stack_effect`
will return the stack effect of jumping. If *jump* is ``False``,
it will return the stack effect of not jumping. And if *jump* is
``None`` (default), it will return the maximal stack effect of both cases.
.. versionadded:: 3.4
.. versionchanged:: 3.8
Added *jump* parameter.
.. versionchanged:: 3.13
If ``oparg`` is omitted (or ``None``), the stack effect is now returned
for ``oparg=0``. Previously this was an error for opcodes that use their
arg. It is also no longer an error to pass an integer ``oparg`` when
the ``opcode`` does not use it; the ``oparg`` in this case is ignored.
.. _bytecodes:
Python Bytecode Instructions
----------------------------
The :func:`get_instructions` function and :class:`Bytecode` class provide
details of bytecode instructions as :class:`Instruction` instances:
.. class:: Instruction
Details for a bytecode operation
.. data:: opcode
numeric code for operation, corresponding to the opcode values listed
below and the bytecode values in the :ref:`opcode_collections`.
.. data:: opname
human readable name for operation
.. data:: baseopcode
numeric code for the base operation if operation is specialized;
otherwise equal to :data:`opcode`
.. data:: baseopname
human readable name for the base operation if operation is specialized;
otherwise equal to :data:`opname`
.. data:: arg
numeric argument to operation (if any), otherwise ``None``
.. data:: oparg
alias for :data:`arg`
.. data:: argval
resolved arg value (if any), otherwise ``None``
.. data:: argrepr
human readable description of operation argument (if any),
otherwise an empty string.
.. data:: offset
start index of operation within bytecode sequence
.. data:: start_offset
start index of operation within bytecode sequence, including prefixed
``EXTENDED_ARG`` operations if present; otherwise equal to :data:`offset`
.. data:: cache_offset
start index of the cache entries following the operation
.. data:: end_offset
end index of the cache entries following the operation
.. data:: starts_line
``True`` if this opcode starts a source line, otherwise ``False``
.. data:: line_number
source line number associated with this opcode (if any), otherwise ``None``
.. data:: is_jump_target
``True`` if other code jumps to here, otherwise ``False``
.. data:: jump_target
bytecode index of the jump target if this is a jump operation,
otherwise ``None``
.. data:: positions
:class:`dis.Positions` object holding the
start and end locations that are covered by this instruction.
.. data:: cache_info
Information about the cache entries of this instruction, as
triplets of the form ``(name, size, data)``, where the ``name``
and ``size`` describe the cache format and data is the contents
of the cache. ``cache_info`` is ``None`` if the instruction does not have
caches.
.. versionadded:: 3.4
.. versionchanged:: 3.11
Field ``positions`` is added.
.. versionchanged:: 3.13
Changed field ``starts_line``.
Added fields ``start_offset``, ``cache_offset``, ``end_offset``,
``baseopname``, ``baseopcode``, ``jump_target``, ``oparg``,
``line_number`` and ``cache_info``.
.. class:: Positions
In case the information is not available, some fields might be ``None``.
.. data:: lineno
.. data:: end_lineno
.. data:: col_offset
.. data:: end_col_offset
.. versionadded:: 3.11
The Python compiler currently generates the following bytecode instructions.
**General instructions**
In the following, We will refer to the interpreter stack as ``STACK`` and describe
operations on it as if it was a Python list. The top of the stack corresponds to
``STACK[-1]`` in this language.
.. opcode:: NOP
Do nothing code. Used as a placeholder by the bytecode optimizer, and to
generate line tracing events.
.. opcode:: NOT_TAKEN
Do nothing code.
Used by the interpreter to record :monitoring-event:`BRANCH_LEFT`
and :monitoring-event:`BRANCH_RIGHT` events for :mod:`sys.monitoring`.
.. versionadded:: 3.14
.. opcode:: POP_ITER
Removes the iterator from the top of the stack.
.. versionadded:: 3.14
.. opcode:: POP_TOP
Removes the top-of-stack item::
STACK.pop()
.. opcode:: END_FOR
Removes the top-of-stack item.
Equivalent to ``POP_TOP``.
Used to clean up at the end of loops, hence the name.
.. versionadded:: 3.12
.. opcode:: END_SEND
Implements ``del STACK[-2]``.
Used to clean up when a generator exits.
.. versionadded:: 3.12
.. opcode:: COPY (i)
Push the i-th item to the top of the stack without removing it from its original
location::
assert i > 0
STACK.append(STACK[-i])
.. versionadded:: 3.11
.. opcode:: SWAP (i)
Swap the top of the stack with the i-th element::
STACK[-i], STACK[-1] = STACK[-1], STACK[-i]
.. versionadded:: 3.11
.. opcode:: CACHE
Rather than being an actual instruction, this opcode is used to mark extra
space for the interpreter to cache useful data directly in the bytecode
itself. It is automatically hidden by all ``dis`` utilities, but can be
viewed with ``show_caches=True``.
Logically, this space is part of the preceding instruction. Many opcodes
expect to be followed by an exact number of caches, and will instruct the
interpreter to skip over them at runtime.
Populated caches can look like arbitrary instructions, so great care should
be taken when reading or modifying raw, adaptive bytecode containing
quickened data.
.. versionadded:: 3.11
**Unary operations**
Unary operations take the top of the stack, apply the operation, and push the
result back on the stack.
.. opcode:: UNARY_NEGATIVE
Implements ``STACK[-1] = -STACK[-1]``.
.. opcode:: UNARY_NOT
Implements ``STACK[-1] = not STACK[-1]``.
.. versionchanged:: 3.13
This instruction now requires an exact :class:`bool` operand.
.. opcode:: UNARY_INVERT
Implements ``STACK[-1] = ~STACK[-1]``.
.. opcode:: GET_ITER
Implements ``STACK[-1] = iter(STACK[-1])``.
.. opcode:: GET_YIELD_FROM_ITER
If ``STACK[-1]`` is a :term:`generator iterator` or :term:`coroutine` object
it is left as is. Otherwise, implements ``STACK[-1] = iter(STACK[-1])``.
.. versionadded:: 3.5
.. opcode:: TO_BOOL
Implements ``STACK[-1] = bool(STACK[-1])``.
.. versionadded:: 3.13
**Binary and in-place operations**
Binary operations remove the top two items from the stack (``STACK[-1]`` and
``STACK[-2]``). They perform the operation, then put the result back on the stack.
In-place operations are like binary operations, but the operation is done in-place
when ``STACK[-2]`` supports it, and the resulting ``STACK[-1]`` may be (but does
not have to be) the original ``STACK[-2]``.
.. opcode:: BINARY_OP (op)
Implements the binary and in-place operators (depending on the value of
*op*)::
rhs = STACK.pop()
lhs = STACK.pop()
STACK.append(lhs op rhs)
.. versionadded:: 3.11
.. versionchanged:: 3.14
With oparg :``NB_SUBSCR``, implements binary subscript (replaces opcode ``BINARY_SUBSCR``)
.. opcode:: STORE_SUBSCR
Implements::
key = STACK.pop()
container = STACK.pop()
value = STACK.pop()
container[key] = value
.. opcode:: DELETE_SUBSCR
Implements::
key = STACK.pop()
container = STACK.pop()
del container[key]
.. opcode:: BINARY_SLICE
Implements::
end = STACK.pop()
start = STACK.pop()
container = STACK.pop()
STACK.append(container[start:end])
.. versionadded:: 3.12
.. opcode:: STORE_SLICE
Implements::
end = STACK.pop()
start = STACK.pop()
container = STACK.pop()
value = STACK.pop()
container[start:end] = value
.. versionadded:: 3.12
**Coroutine opcodes**
.. opcode:: GET_AWAITABLE (where)
Implements ``STACK[-1] = get_awaitable(STACK[-1])``, where ``get_awaitable(o)``
returns ``o`` if ``o`` is a coroutine object or a generator object with
the :data:`~inspect.CO_ITERABLE_COROUTINE` flag, or resolves
``o.__await__``.
If the ``where`` operand is nonzero, it indicates where the instruction
occurs:
* ``1``: After a call to ``__aenter__``
* ``2``: After a call to ``__aexit__``
.. versionadded:: 3.5
.. versionchanged:: 3.11
Previously, this instruction did not have an oparg.
.. opcode:: GET_AITER
Implements ``STACK[-1] = STACK[-1].__aiter__()``.
.. versionadded:: 3.5
.. versionchanged:: 3.7
Returning awaitable objects from ``__aiter__`` is no longer
supported.
.. opcode:: GET_ANEXT
Implement ``STACK.append(get_awaitable(STACK[-1].__anext__()))`` to the stack.
See ``GET_AWAITABLE`` for details about ``get_awaitable``.
.. versionadded:: 3.5
.. opcode:: END_ASYNC_FOR
Terminates an :keyword:`async for` loop. Handles an exception raised
when awaiting a next item. The stack contains the async iterable in
``STACK[-2]`` and the raised exception in ``STACK[-1]``. Both are popped.
If the exception is not :exc:`StopAsyncIteration`, it is re-raised.
.. versionadded:: 3.8
.. versionchanged:: 3.11
Exception representation on the stack now consist of one, not three, items.
.. opcode:: CLEANUP_THROW
Handles an exception raised during a :meth:`~generator.throw` or
:meth:`~generator.close` call through the current frame. If ``STACK[-1]`` is an
instance of :exc:`StopIteration`, pop three values from the stack and push
its ``value`` member. Otherwise, re-raise ``STACK[-1]``.
.. versionadded:: 3.12
**Miscellaneous opcodes**
.. opcode:: SET_ADD (i)
Implements::
item = STACK.pop()
set.add(STACK[-i], item)
Used to implement set comprehensions.
.. opcode:: LIST_APPEND (i)
Implements::
item = STACK.pop()
list.append(STACK[-i], item)
Used to implement list comprehensions.
.. opcode:: MAP_ADD (i)
Implements::
value = STACK.pop()
key = STACK.pop()
dict.__setitem__(STACK[-i], key, value)
Used to implement dict comprehensions.
.. versionadded:: 3.1
.. versionchanged:: 3.8
Map value is ``STACK[-1]`` and map key is ``STACK[-2]``. Before, those
were reversed.
For all of the :opcode:`SET_ADD`, :opcode:`LIST_APPEND` and :opcode:`MAP_ADD`
instructions, while the added value or key/value pair is popped off, the
container object remains on the stack so that it is available for further
iterations of the loop.
.. opcode:: RETURN_VALUE
Returns with ``STACK[-1]`` to the caller of the function.
.. opcode:: YIELD_VALUE
Yields ``STACK.pop()`` from a :term:`generator`.
.. versionchanged:: 3.11
oparg set to be the stack depth.
.. versionchanged:: 3.12
oparg set to be the exception block depth, for efficient closing of generators.
.. versionchanged:: 3.13
oparg is ``1`` if this instruction is part of a yield-from or await, and ``0``
otherwise.
.. opcode:: SETUP_ANNOTATIONS
Checks whether ``__annotations__`` is defined in ``locals()``, if not it is
set up to an empty ``dict``. This opcode is only emitted if a class
or module body contains :term:`variable annotations <variable annotation>`
statically.
.. versionadded:: 3.6
.. opcode:: POP_EXCEPT
Pops a value from the stack, which is used to restore the exception state.
.. versionchanged:: 3.11
Exception representation on the stack now consist of one, not three, items.
.. opcode:: RERAISE
Re-raises the exception currently on top of the stack. If oparg is non-zero,
pops an additional value from the stack which is used to set
:attr:`~frame.f_lasti` of the current frame.
.. versionadded:: 3.9
.. versionchanged:: 3.11
Exception representation on the stack now consist of one, not three, items.
.. opcode:: PUSH_EXC_INFO
Pops a value from the stack. Pushes the current exception to the top of the stack.
Pushes the value originally popped back to the stack.
Used in exception handlers.
.. versionadded:: 3.11
.. opcode:: CHECK_EXC_MATCH
Performs exception matching for ``except``. Tests whether the ``STACK[-2]``
is an exception matching ``STACK[-1]``. Pops ``STACK[-1]`` and pushes the boolean
result of the test.
.. versionadded:: 3.11
.. opcode:: CHECK_EG_MATCH
Performs exception matching for ``except*``. Applies ``split(STACK[-1])`` on
the exception group representing ``STACK[-2]``.
In case of a match, pops two items from the stack and pushes the
non-matching subgroup (``None`` in case of full match) followed by the
matching subgroup. When there is no match, pops one item (the match
type) and pushes ``None``.
.. versionadded:: 3.11
.. opcode:: WITH_EXCEPT_START
Calls the function in position 4 on the stack with arguments (type, val, tb)
representing the exception at the top of the stack.
Used to implement the call ``context_manager.__exit__(*exc_info())`` when an exception
has occurred in a :keyword:`with` statement.
.. versionadded:: 3.9
.. versionchanged:: 3.11
The ``__exit__`` function is in position 4 of the stack rather than 7.
Exception representation on the stack now consist of one, not three, items.
.. opcode:: LOAD_COMMON_CONSTANT
Pushes a common constant onto the stack. The interpreter contains a hardcoded
list of constants supported by this instruction. Used by the :keyword:`assert`