path: root/Doc/library/dis.rst

: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``.


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           0 RESUME                   0
   <BLANKLINE>
     3           2 LOAD_GLOBAL              1 (NULL + len)
                14 LOAD_FAST                0 (alist)
                16 PRECALL                  1
                20 CALL                     1
                30 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] [infile]

The following options are accepted:

.. program:: dis

.. cmdoption:: -h, --help

   Display usage and exit.

.. cmdoption:: -C, --show-caches

   Show inline caches.

If :file:`infile` is specified, its disassembled code will be written to stdout.
Otherwise, disassembly is performed on compiled source code recieved 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)

   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.

   .. 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.

Example:

.. doctest::

    >>> bytecode = dis.Bytecode(myfunc)
    >>> for instr in bytecode:
    ...     print(instr.opname)
    ...
    RESUME
    LOAD_GLOBAL
    LOAD_FAST
    PRECALL
    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)

   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 (the code of
   comprehensions, generator expressions and nested functions, and the code
   used for building nested classes).
   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.

   .. 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.


.. function:: distb(tb=None, *, file=None, show_caches=False, adaptive=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.


.. function:: disassemble(code, lasti=-1, *, file=None, show_caches=False, adaptive=False)
              disco(code, lasti=-1, *, file=None, show_caches=False, adaptive=False)

   Disassemble a code object, indicating the last instruction if *lasti* was
   provided.  The output is divided in the following columns:

   #. the line number, for the first instruction of each line
   #. 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.


.. function:: get_instructions(x, *, first_line=None, show_caches=False, adaptive=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 *show_caches* and *adaptive* parameters work as they do in :func:`dis`.

   .. versionadded:: 3.4

   .. versionchanged:: 3.11
      Added the *show_caches* and *adaptive* parameters.


.. 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>`.


.. 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.


.. _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:: arg

      numeric argument to operation (if any), otherwise ``None``


   .. 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:: starts_line

      line started by this opcode (if any), otherwise ``None``


   .. data:: is_jump_target

      ``True`` if other code jumps to here, otherwise ``False``


   .. data:: positions

      :class:`dis.Positions` object holding the
      start and end locations that are covered by this instruction.

   .. versionadded:: 3.4

   .. versionchanged:: 3.11

      Field ``positions`` is added.


.. 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**

.. opcode:: NOP

   Do nothing code.  Used as a placeholder by the bytecode optimizer, and to
   generate line tracing events.


.. opcode:: POP_TOP

   Removes the top-of-stack (TOS) item.


.. opcode:: COPY (i)

   Push the *i*-th item to the top of the stack. The item is not removed from its
   original location.

   .. versionadded:: 3.11


.. opcode:: SWAP (i)

   Swap TOS with the item at position *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_POSITIVE

   Implements ``TOS = +TOS``.


.. opcode:: UNARY_NEGATIVE

   Implements ``TOS = -TOS``.


.. opcode:: UNARY_NOT

   Implements ``TOS = not TOS``.


.. opcode:: UNARY_INVERT

   Implements ``TOS = ~TOS``.


.. opcode:: GET_ITER

   Implements ``TOS = iter(TOS)``.


.. opcode:: GET_YIELD_FROM_ITER

   If ``TOS`` is a :term:`generator iterator` or :term:`coroutine` object
   it is left as is.  Otherwise, implements ``TOS = iter(TOS)``.

   .. versionadded:: 3.5


**Binary and in-place operations**

Binary operations remove the top of the stack (TOS) and the second top-most
stack item (TOS1) from the stack.  They perform the operation, and put the
result back on the stack.

In-place operations are like binary operations, in that they remove TOS and
TOS1, and push the result back on the stack, but the operation is done in-place
when TOS1 supports it, and the resulting TOS may be (but does not have to be)
the original TOS1.


.. opcode:: BINARY_OP (op)

   Implements the binary and in-place operators (depending on the value of
   *op*).

   .. versionadded:: 3.11


.. opcode:: BINARY_SUBSCR

   Implements ``TOS = TOS1[TOS]``.


.. opcode:: STORE_SUBSCR

   Implements ``TOS1[TOS] = TOS2``.


.. opcode:: DELETE_SUBSCR

   Implements ``del TOS1[TOS]``.


**Coroutine opcodes**

.. opcode:: GET_AWAITABLE (where)

   Implements ``TOS = get_awaitable(TOS)``, where ``get_awaitable(o)``
   returns ``o`` if ``o`` is a coroutine object or a generator object with
   the 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 ``TOS = TOS.__aiter__()``.

   .. versionadded:: 3.5
   .. versionchanged:: 3.7
      Returning awaitable objects from ``__aiter__`` is no longer
      supported.


.. opcode:: GET_ANEXT

   Pushes ``get_awaitable(TOS.__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
   TOS1 and the raised exception in TOS. 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:: BEFORE_ASYNC_WITH

   Resolves ``__aenter__`` and ``__aexit__`` from the object on top of the
   stack.  Pushes ``__aexit__`` and result of ``__aenter__()`` to the stack.

   .. versionadded:: 3.5



**Miscellaneous opcodes**

.. opcode:: PRINT_EXPR

   Implements the expression statement for the interactive mode.  TOS is removed
   from the stack and printed.  In non-interactive mode, an expression statement
   is terminated with :opcode:`POP_TOP`.


.. opcode:: SET_ADD (i)

   Calls ``set.add(TOS1[-i], TOS)``.  Used to implement set comprehensions.


.. opcode:: LIST_APPEND (i)

   Calls ``list.append(TOS1[-i], TOS)``.  Used to implement list comprehensions.


.. opcode:: MAP_ADD (i)

   Calls ``dict.__setitem__(TOS1[-i], TOS1, TOS)``.  Used to implement dict
   comprehensions.

   .. versionadded:: 3.1
   .. versionchanged:: 3.8
      Map value is TOS and map key is TOS1. 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 TOS to the caller of the function.


.. opcode:: YIELD_VALUE

   Pops TOS and yields it from a :term:`generator`.



.. 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:: IMPORT_STAR

   Loads all symbols not starting with ``'_'`` directly from the module TOS to
   the local namespace. The module is popped after loading all names. This
   opcode implements ``from module import *``.


.. 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 TOS1 is an exception
   matching TOS. Pops TOS and pushes the boolean result of the test.

   .. versionadded:: 3.11

.. opcode:: CHECK_EG_MATCH

   Performs exception matching for ``except*``. Applies ``split(TOS)`` on
   the exception group representing TOS1.

   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:: PREP_RERAISE_STAR

   Combines the raised and reraised exceptions list from TOS, into an exception
   group to propagate from a try-except* block. Uses the original exception
   group from TOS1 to reconstruct the structure of reraised exceptions. Pops
   two items from the stack and pushes the exception to reraise or ``None``
   if there isn't one.

   .. 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_ASSERTION_ERROR

   Pushes :exc:`AssertionError` onto the stack.  Used by the :keyword:`assert`
   statement.

   .. versionadded:: 3.9


.. opcode:: LOAD_BUILD_CLASS

   Pushes :func:`builtins.__build_class__` onto the stack.  It is later called
   to construct a class.


.. opcode:: BEFORE_WITH (delta)

   This opcode performs several operations before a with block starts.  First,
   it loads :meth:`~object.__exit__` from the context manager and pushes it onto
   the stack for later use by :opcode:`WITH_EXCEPT_START`.  Then,
   :meth:`~object.__enter__` is called. Finally, the result of calling the
   ``__enter__()`` method is pushed onto the stack.

   .. versionadded:: 3.11


.. opcode:: GET_LEN

   Push ``len(TOS)`` onto the stack.

   .. versionadded:: 3.10


.. opcode:: MATCH_MAPPING

   If TOS is an instance of :class:`collections.abc.Mapping` (or, more technically: if
   it has the :c:macro:`Py_TPFLAGS_MAPPING` flag set in its
   :c:member:`~PyTypeObject.tp_flags`), push ``True`` onto the stack.  Otherwise, push
   ``False``.

   .. versionadded:: 3.10


.. opcode:: MATCH_SEQUENCE

   If TOS is an instance of :class:`collections.abc.Sequence` and is *not* an instance
   of :class:`str`/:class:`bytes`/:class:`bytearray` (or, more technically: if it has
   the :c:macro:`Py_TPFLAGS_SEQUENCE` flag set in its :c:member:`~PyTypeObject.tp_flags`),
   push ``True`` onto the stack.  Otherwise, push ``False``.

   .. versionadded:: 3.10


.. opcode:: MATCH_KEYS

   TOS is a tuple of mapping keys, and TOS1 is the match subject.  If TOS1
   contains all of the keys in TOS, push a :class:`tuple` containing the
   corresponding values. Otherwise, push ``None``.

   .. versionadded:: 3.10

   .. versionchanged:: 3.11
      Previously, this instruction also pushed a boolean value indicating
      success (``True``) or failure (``False``).


.. opcode:: STORE_NAME (namei)

   Implements ``name = TOS``. *namei* is the index of *name* in the attribute
   :attr:`~codeobject.co_names` of the :ref:`code object <code-objects>`.
   The compiler tries to use
   :opcode:`STORE_FAST` or :opcode:`STORE_GLOBAL` if possible.


.. opcode:: DELETE_NAME (namei)

   Implements ``del name``, where *namei* is the index into :attr:`~codeobject.co_names`
   attribute of the :ref:`code object <code-objects>`.


.. opcode:: UNPACK_SEQUENCE (count)

   Unpacks TOS into *count* individual values, which are put onto the stack
   right-to-left.


.. opcode:: UNPACK_EX (counts)

   Implements assignment with a starred target: Unpacks an iterable in TOS into
   individual values, where the total number of values can be smaller than the
   number of items in the iterable: one of the new values will be a list of all
   leftover items.

   The low byte of *counts* is the number of values before the list value, the
   high byte of *counts* the number of values after it.  The resulting values
   are put onto the stack right-to-left.


.. opcode:: STORE_ATTR (namei)

   Implements ``TOS.name = TOS1``, where *namei* is the index of name in
   :attr:`co_names`.


.. opcode:: DELETE_ATTR (namei)

   Implements ``del TOS.name``, using *namei* as index into
   :attr:`~codeobject.co_names` of the :ref:`code object <code-objects>`.


.. opcode:: STORE_GLOBAL (namei)

   Works as :opcode:`STORE_NAME`, but stores the name as a global.


.. opcode:: DELETE_GLOBAL (namei)

   Works as :opcode:`DELETE_NAME`, but deletes a global name.


.. opcode:: LOAD_CONST (consti)

   Pushes ``co_consts[consti]`` onto the stack.


.. opcode:: LOAD_NAME (namei)

   Pushes the value associated with ``co_names[namei]`` onto the stack.


.. opcode:: BUILD_TUPLE (count)

   Creates a tuple consuming *count* items from the stack, and pushes the
   resulting tuple onto the stack.


.. opcode:: BUILD_LIST (count)

   Works as :opcode:`BUILD_TUPLE`, but creates a list.


.. opcode:: BUILD_SET (count)

   Works as :opcode:`BUILD_TUPLE`, but creates a set.


.. opcode:: BUILD_MAP (count)

   Pushes a new dictionary object onto the stack.  Pops ``2 * count`` items
   so that the dictionary holds *count* entries:
   ``{..., TOS3: TOS2, TOS1: TOS}``.

   .. versionchanged:: 3.5
      The dictionary is created from stack items instead of creating an
      empty dictionary pre-sized to hold *count* items.


.. opcode:: BUILD_CONST_KEY_MAP (count)

   The version of :opcode:`BUILD_MAP` specialized for constant keys. Pops the
   top element on the stack which contains a tuple of keys, then starting from
   ``TOS1``, pops *count* values to form values in the built dictionary.

   .. versionadded:: 3.6


.. opcode:: BUILD_STRING (count)

   Concatenates *count* strings from the stack and pushes the resulting string
   onto the stack.

   .. versionadded:: 3.6


.. opcode:: LIST_TO_TUPLE

   Pops a list from the stack and pushes a tuple containing the same values.

   .. versionadded:: 3.9


.. opcode:: LIST_EXTEND (i)

   Calls ``list.extend(TOS1[-i], TOS)``.  Used to build lists.

   .. versionadded:: 3.9


.. opcode:: SET_UPDATE (i)

   Calls ``set.update(TOS1[-i], TOS)``.  Used to build sets.

   .. versionadded:: 3.9


.. opcode:: DICT_UPDATE (i)

   Calls ``dict.update(TOS1[-i], TOS)``.  Used to build dicts.

   .. versionadded:: 3.9


.. opcode:: DICT_MERGE (i)

   Like :opcode:`DICT_UPDATE` but raises an exception for duplicate keys.

   .. versionadded:: 3.9


.. opcode:: LOAD_ATTR (namei)

   Replaces TOS with ``getattr(TOS, co_names[namei])``.


.. opcode:: COMPARE_OP (opname)

   Performs a Boolean operation.  The operation name can be found in
   ``cmp_op[opname]``.


.. opcode:: IS_OP (invert)

   Performs ``is`` comparison, or ``is not`` if ``invert`` is 1.

   .. versionadded:: 3.9


.. opcode:: CONTAINS_OP (invert)

   Performs ``in`` comparison, or ``not in`` if ``invert`` is 1.

   .. versionadded:: 3.9


.. opcode:: IMPORT_NAME (namei)

   Imports the module ``co_names[namei]``.  TOS and TOS1 are popped and provide
   the *fromlist* and *level* arguments of :func:`__import__`.  The module
   object is pushed onto the stack.  The current namespace is not affected: for
   a proper import statement, a subsequent :opcode:`STORE_FAST` instruction
   modifies the namespace.


.. opcode:: IMPORT_FROM (namei)

   Loads the attribute ``co_names[namei]`` from the module found in TOS. The
   resulting object is pushed onto the stack, to be subsequently stored by a
   :opcode:`STORE_FAST` instruction.


.. opcode:: JUMP_FORWARD (delta)

   Increments bytecode counter by *delta*.


.. opcode:: JUMP_BACKWARD (delta)

   Decrements bytecode counter by *delta*. Checks for interrupts.

   .. versionadded:: 3.11


.. opcode:: JUMP_BACKWARD_NO_INTERRUPT (delta)

   Decrements bytecode counter by *delta*. Does not check for interrupts.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_FORWARD_IF_TRUE (delta)

   If TOS is true, increments the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_BACKWARD_IF_TRUE (delta)

   If TOS is true, decrements the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_FORWARD_IF_FALSE (delta)

   If TOS is false, increments the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_BACKWARD_IF_FALSE (delta)

   If TOS is false, decrements the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_FORWARD_IF_NOT_NONE (delta)

   If TOS is not ``None``, increments the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_BACKWARD_IF_NOT_NONE (delta)

   If TOS is not ``None``, decrements the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_FORWARD_IF_NONE (delta)

   If TOS is ``None``, increments the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: POP_JUMP_BACKWARD_IF_NONE (delta)

   If TOS is ``None``, decrements the bytecode counter by *delta*.  TOS is popped.

   .. versionadded:: 3.11


.. opcode:: JUMP_IF_TRUE_OR_POP (delta)

   If TOS is true, increments the bytecode counter by *delta* and leaves TOS on the
   stack.  Otherwise (TOS is false), TOS is popped.

   .. versionadded:: 3.1

   .. versionchanged:: 3.11
      The oparg is now a relative delta rather than an absolute target.

.. opcode:: JUMP_IF_FALSE_OR_POP (delta)

   If TOS is false, increments the bytecode counter by *delta* and leaves TOS on the
   stack.  Otherwise (TOS is true), TOS is popped.

   .. versionadded:: 3.1

   .. versionchanged:: 3.11
      The oparg is now a relative delta rather than an absolute target.


.. opcode:: FOR_ITER (delta)

   TOS is an :term:`iterator`.  Call its :meth:`~iterator.__next__` method.  If
   this yields a new value, push it on the stack (leaving the iterator below
   it).  If the iterator indicates it is exhausted, TOS is popped, and the byte
   code counter is incremented by *delta*.


.. opcode:: LOAD_GLOBAL (namei)

   Loads the global named ``co_names[namei>>1]`` onto the stack.

   .. versionchanged:: 3.11
      If the low bit of ``namei`` is set, then a ``NULL`` is pushed to the
      stack before the global variable.

.. opcode:: LOAD_FAST (var_num)

   Pushes a reference to the local ``co_varnames[var_num]`` onto the stack.


.. opcode:: STORE_FAST (var_num)

   Stores TOS into the local ``co_varnames[var_num]``.


.. opcode:: DELETE_FAST (var_num)

   Deletes local ``co_varnames[var_num]``.


.. opcode:: MAKE_CELL (i)

   Creates a new cell in slot ``i``.  If that slot is nonempty then
   that value is stored into the new cell.

   .. versionadded:: 3.11


.. opcode:: LOAD_CLOSURE (i)

   Pushes a reference to the cell contained in slot ``i`` of the "fast locals"
   storage.  The name of the variable is ``co_fastlocalnames[i]``.

   Note that ``LOAD_CLOSURE`` is effectively an alias for ``LOAD_FAST``.
   It exists to keep bytecode a little more readable.

   .. versionchanged:: 3.11
      ``i`` is no longer offset by the length of ``co_varnames``.


.. opcode:: LOAD_DEREF (i)

   Loads the cell contained in slot ``i`` of the "fast locals" storage.
   Pushes a reference to the object the cell contains on the stack.

   .. versionchanged:: 3.11
      ``i`` is no longer offset by the length of :attr:`~codeobject.co_varnames`.


.. opcode:: LOAD_CLASSDEREF (i)

   Much like :opcode:`LOAD_DEREF` but first checks the locals dictionary before
   consulting the cell.  This is used for loading free variables in class
   bodies.

   .. versionadded:: 3.4

   .. versionchanged:: 3.11
      ``i`` is no longer offset by the length of ``co_varnames``.


.. opcode:: STORE_DEREF (i)

   Stores TOS into the cell contained in slot ``i`` of the "fast locals"
   storage.

   .. versionchanged:: 3.11
      ``i`` is no longer offset by the length of :attr:`~codeobject.co_varnames`.


.. opcode:: DELETE_DEREF (i)

   Empties the cell contained in slot ``i`` of the "fast locals" storage.
   Used by the :keyword:`del` statement.

   .. versionadded:: 3.2

   .. versionchanged:: 3.11
      ``i`` is no longer offset by the length of :attr:`~codeobject.co_varnames`.


.. opcode:: COPY_FREE_VARS (n)

   Copies the ``n`` free variables from the closure into the frame.
   Removes the need for special code on the caller's side when calling
   closures.

   .. versionadded:: 3.11


.. opcode:: RAISE_VARARGS (argc)

   Raises an exception using one of the 3 forms of the ``raise`` statement,
   depending on the value of *argc*:

   * 0: ``raise`` (re-raise previous exception)
   * 1: ``raise TOS`` (raise exception instance or type at ``TOS``)
   * 2: ``raise TOS1 from TOS`` (raise exception instance or type at ``TOS1``
     with ``__cause__`` set to ``TOS``)


.. opcode:: CALL (argc)

   Calls a callable object with the number of arguments specified by ``argc``,
   including the named arguments specified by the preceding
   :opcode:`KW_NAMES`, if any.
   On the stack are (in ascending order), either:

   * NULL
   * The callable
   * The positional arguments
   * The named arguments

   or:

   * The callable
   * ``self``
   * The remaining positional arguments
   * The named arguments

   ``argc`` is the total of the positional and named arguments, excluding
   ``self`` when a ``NULL`` is not present.

   ``CALL`` pops all arguments and the callable object off the stack,
   calls the callable object with those arguments, and pushes the return value
   returned by the callable object.

   .. versionadded:: 3.11


.. opcode:: CALL_FUNCTION_EX (flags)

   Calls a callable object with variable set of positional and keyword
   arguments.  If the lowest bit of *flags* is set, the top of the stack
   contains a mapping object containing additional keyword arguments.
   Before the callable is called, the mapping object and iterable object
   are each "unpacked" and their contents passed in as keyword and
   positional arguments respectively.
   ``CALL_FUNCTION_EX`` pops all arguments and the callable object off the stack,
   calls the callable object with those arguments, and pushes the return value
   returned by the callable object.

   .. versionadded:: 3.6


.. opcode:: LOAD_METHOD (namei)

   Loads a method named ``co_names[namei]`` from the TOS object. TOS is popped.
   This bytecode distinguishes two cases: if TOS has a method with the correct
   name, the bytecode pushes the unbound method and TOS. TOS will be used as
   the first argument (``self``) by :opcode:`CALL` when calling the
   unbound method. Otherwise, ``NULL`` and the object return by the attribute
   lookup are pushed.

   .. versionadded:: 3.7


.. opcode:: PRECALL (argc)

   Prefixes :opcode:`CALL`. Logically this is a no op.
   It exists to enable effective specialization of calls.
   ``argc`` is the number of arguments as described in :opcode:`CALL`.

   .. versionadded:: 3.11


.. opcode:: PUSH_NULL

    Pushes a ``NULL`` to the stack.
    Used in the call sequence to match the ``NULL`` pushed by
    :opcode:`LOAD_METHOD` for non-method calls.

   .. versionadded:: 3.11


.. opcode:: KW_NAMES (i)

   Prefixes :opcode:`PRECALL`.
   Stores a reference to ``co_consts[consti]`` into an internal variable
   for use by :opcode:`CALL`. ``co_consts[consti]`` must be a tuple of strings.

   .. versionadded:: 3.11


.. opcode:: MAKE_FUNCTION (flags)

   Pushes a new function object on the stack.  From bottom to top, the consumed
   stack must consist of values if the argument carries a specified flag value

   * ``0x01`` a tuple of default values for positional-only and
     positional-or-keyword parameters in positional order
   * ``0x02`` a dictionary of keyword-only parameters' default values
   * ``0x04`` a tuple of strings containing parameters' annotations
   * ``0x08`` a tuple containing cells for free variables, making a closure
   * the code associated with the function (at TOS)

   .. versionchanged:: 3.10
      Flag value ``0x04`` is a tuple of strings instead of dictionary

   .. versionchanged:: 3.11
      Qualified name at TOS was removed.


.. opcode:: BUILD_SLICE (argc)

   .. index:: pair: built-in function; slice

   Pushes a slice object on the stack.  *argc* must be 2 or 3.  If it is 2,
   ``slice(TOS1, TOS)`` is pushed; if it is 3, ``slice(TOS2, TOS1, TOS)`` is
   pushed. See the :func:`slice` built-in function for more information.


.. opcode:: EXTENDED_ARG (ext)

   Prefixes any opcode which has an argument too big to fit into the default one
   byte. *ext* holds an additional byte which act as higher bits in the argument.
   For each opcode, at most three prefixal ``EXTENDED_ARG`` are allowed, forming
   an argument from two-byte to four-byte.


.. opcode:: FORMAT_VALUE (flags)

   Used for implementing formatted literal strings (f-strings).  Pops
   an optional *fmt_spec* from the stack, then a required *value*.
   *flags* is interpreted as follows:

   * ``(flags & 0x03) == 0x00``: *value* is formatted as-is.
   * ``(flags & 0x03) == 0x01``: call :func:`str` on *value* before
     formatting it.
   * ``(flags & 0x03) == 0x02``: call :func:`repr` on *value* before
     formatting it.
   * ``(flags & 0x03) == 0x03``: call :func:`ascii` on *value* before
     formatting it.
   * ``(flags & 0x04) == 0x04``: pop *fmt_spec* from the stack and use
     it, else use an empty *fmt_spec*.

   Formatting is performed using :c:func:`PyObject_Format`.  The
   result is pushed on the stack.

   .. versionadded:: 3.6


.. opcode:: MATCH_CLASS (count)

   TOS is a tuple of keyword attribute names, TOS1 is the class being matched
   against, and TOS2 is the match subject.  *count* is the number of positional
   sub-patterns.

   Pop TOS, TOS1, and TOS2.  If TOS2 is an instance of TOS1 and has the
   positional and keyword attributes required by *count* and TOS, push a tuple
   of extracted attributes.  Otherwise, push ``None``.

   .. versionadded:: 3.10

   .. versionchanged:: 3.11
      Previously, this instruction also pushed a boolean value indicating
      success (``True``) or failure (``False``).


.. opcode:: RESUME (where)

    A no-op. Performs internal tracing, debugging and optimization checks.

    The ``where`` operand marks where the ``RESUME`` occurs:

    * ``0`` The start of a function
    * ``1`` After a ``yield`` expression
    * ``2`` After a ``yield from`` expression
    * ``3`` After an ``await`` expression

   .. versionadded:: 3.11


.. opcode:: RETURN_GENERATOR

    Create a generator, coroutine, or async generator from the current frame.
    Clear the current frame and return the newly created generator.

    .. versionadded:: 3.11


.. opcode:: SEND

    Sends ``None`` to the sub-generator of this generator.
    Used in ``yield from`` and ``await`` statements.

    .. versionadded:: 3.11


.. opcode:: ASYNC_GEN_WRAP

    Wraps the value on top of the stack in an ``async_generator_wrapped_value``.
    Used to yield in async generators.

    .. versionadded:: 3.11


.. opcode:: HAVE_ARGUMENT

   This is not really an opcode.  It identifies the dividing line between
   opcodes which don't use their argument and those that do
   (``< HAVE_ARGUMENT`` and ``>= HAVE_ARGUMENT``, respectively).

   .. versionchanged:: 3.6
      Now every instruction has an argument, but opcodes ``< HAVE_ARGUMENT``
      ignore it. Before, only opcodes ``>= HAVE_ARGUMENT`` had an argument.


.. _opcode_collections:

Opcode collections
------------------

These collections are provided for automatic introspection of bytecode
instructions:

.. data:: opname

   Sequence of operation names, indexable using the bytecode.


.. data:: opmap

   Dictionary mapping operation names to bytecodes.


.. data:: cmp_op

   Sequence of all compare operation names.


.. data:: hasconst

   Sequence of bytecodes that access a constant.


.. data:: hasfree

   Sequence of bytecodes that access a free variable (note that 'free' in this
   context refers to names in the current scope that are referenced by inner
   scopes or names in outer scopes that are referenced from this scope.  It does
   *not* include references to global or builtin scopes).


.. data:: hasname

   Sequence of bytecodes that access an attribute by name.


.. data:: hasjrel

   Sequence of bytecodes that have a relative jump target.


.. data:: hasjabs

   Sequence of bytecodes that have an absolute jump target.


.. data:: haslocal

   Sequence of bytecodes that access a local variable.


.. data:: hascompare

   Sequence of bytecodes of Boolean operations.