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cpython/Doc/library/dis.rst
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GH-88691: Shrink the CALL caches (GH-103230)
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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``.
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)
12 LOAD_FAST 0 (alist)
14 CALL 1
22 RETURN_VALUE
(The "2" is a line number).
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
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 ``co_lines`` method
of the code object *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` ``co_lines`` method is used instead of the ``co_firstlineno``
and ``co_lnotab`` attributes of the code object.
.. 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**
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:: POP_TOP
Removes the top-of-stack item.::
STACK.pop()
.. opcode:: END_FOR
Removes the top two values from the stack.
Equivalent to POP_TOP; POP_TOP.
Used to clean up at the end of loops, hence the name.
.. 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]``.
.. 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
**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
.. opcode:: BINARY_SUBSCR
Implements::
key = STACK.pop()
container = STACK.pop()
STACK.append(container[index])
.. 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()
values = 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 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
.. opcode:: BEFORE_ASYNC_WITH
Resolves ``__aenter__`` and ``__aexit__`` from ``STACK[-1]``.
Pushes ``__aexit__`` and result of ``__aenter__()`` to the stack::
STACK.extend((__aexit__, __aenter__())
.. versionadded:: 3.5
**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:: RETURN_CONST (consti)
Returns with ``co_consts[consti]`` to the caller of the function.
.. versionadded:: 3.12
.. 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.
.. 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 ``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_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
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
Perform ``STACK.append(len(STACK[-1]))``.
.. versionadded:: 3.10
.. opcode:: MATCH_MAPPING
If ``STACK[-1]`` is an instance of :class:`collections.abc.Mapping` (or, more
technically: if it has the :const:`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 ``STACK[-1]`` 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 :const:`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
``STACK[-1]`` is a tuple of mapping keys, and ``STACK[-2]`` is the match subject.
If ``STACK[-2]`` contains all of the keys in ``STACK[-1]``, 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 = STACK.pop()``. *namei* is the index of *name* in the attribute
:attr:`co_names` of the code object. 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:`co_names`
attribute of the code object.
.. opcode:: UNPACK_SEQUENCE (count)
Unpacks ``STACK[-1]`` into *count* individual values, which are put onto the stack
right-to-left.::
STACK.extend(STACK.pop()[:count:-1])
.. opcode:: UNPACK_EX (counts)
Implements assignment with a starred target: Unpacks an iterable in ``STACK[-1]``
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 number of values before and after the list value is limited to 255.
The number of values before the list value is encoded in the argument of the
opcode. The number of values after the list if any is encoded using an
``EXTENDED_ARG``. As a consequence, the argument can be seen as a two bytes values
where 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 extracted values are put onto the stack right-to-left, i.e. ``a, *b, c = d``
will be stored after execution as ``STACK.extend((a, b, c))``.
.. opcode:: STORE_ATTR (namei)
Implements::
obj = STACK.pop()
value = STACK.pop()
obj.name = value
where *namei* is the index of name in :attr:`co_names`.
.. opcode:: DELETE_ATTR (namei)
Implements::
obj = STACK.pop()
del obj.name
where *namei* is the index of name into :attr:`co_names`.
.. 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.::
assert count > 0
STACK, values = STACK[:-count], STACK[-count:]
STACK.append(tuple(values))
.. 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:
``{..., STACK[-4]: STACK[-3], STACK[-2]: STACK[-1]}``.
.. 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
``STACK[-2]``, 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_EXTEND (i)
Implements::
seq = STACK.pop()
list.extend(STACK[-i], seq)
Used to build lists.
.. versionadded:: 3.9
.. opcode:: SET_UPDATE (i)
Implements::
seq = STACK.pop()
set.update(STACK[-i], seq)
Used to build sets.
.. versionadded:: 3.9
.. opcode:: DICT_UPDATE (i)
Implements::
map = STACK.pop()
dict.update(STACK[-i], map)
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)
If the low bit of ``namei`` is not set, this replaces ``STACK[-1]`` with
``getattr(STACK[-1], co_names[namei>>1])``.
If the low bit of ``namei`` is set, this will attempt to load a method named
``co_names[namei>>1]`` from the ``STACK[-1]`` object. ``STACK[-1]`` is popped.
This bytecode distinguishes two cases: if ``STACK[-1]`` has a method with the
correct name, the bytecode pushes the unbound method and ``STACK[-1]``.
``STACK[-1]`` 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.
.. versionchanged:: 3.12
If the low bit of ``namei`` is set, then a ``NULL`` or ``self`` is
pushed to the stack before the attribute or unbound method respectively.
.. 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]``. ``STACK[-1]`` and ``STACK[-2]`` 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 ``STACK[-1]``.
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_IF_TRUE (delta)
If ``STACK[-1]`` is true, increments the bytecode counter by *delta*.
``STACK[-1]`` is popped.
.. versionchanged:: 3.11
The oparg is now a relative delta rather than an absolute target.
This opcode is a pseudo-instruction, replaced in final bytecode by
the directed versions (forward/backward).
.. versionchanged:: 3.12
This is no longer a pseudo-instruction.
.. opcode:: POP_JUMP_IF_FALSE (delta)
If ``STACK[-1]`` is false, increments the bytecode counter by *delta*.
``STACK[-1]`` is popped.
.. versionchanged:: 3.11
The oparg is now a relative delta rather than an absolute target.
This opcode is a pseudo-instruction, replaced in final bytecode by
the directed versions (forward/backward).
.. versionchanged:: 3.12
This is no longer a pseudo-instruction.
.. opcode:: POP_JUMP_IF_NOT_NONE (delta)
If ``STACK[-1]`` is not ``None``, increments the bytecode counter by *delta*.
``STACK[-1]`` is popped.
This opcode is a pseudo-instruction, replaced in final bytecode by
the directed versions (forward/backward).
.. versionadded:: 3.11
.. versionchanged:: 3.12
This is no longer a pseudo-instruction.
.. opcode:: POP_JUMP_IF_NONE (delta)
If ``STACK[-1]`` is ``None``, increments the bytecode counter by *delta*.
``STACK[-1]`` is popped.
This opcode is a pseudo-instruction, replaced in final bytecode by
the directed versions (forward/backward).
.. versionadded:: 3.11
.. versionchanged:: 3.12
This is no longer a pseudo-instruction.
.. opcode:: FOR_ITER (delta)
``STACK[-1]`` 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 then the byte code counter is
incremented by *delta*.
.. versionchanged:: 3.12
Up until 3.11 the iterator was popped when it was exhausted.
.. 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.
.. versionchanged:: 3.12
This opcode is now only used in situations where the local variable is
guaranteed to be initialized. It cannot raise :exc:`UnboundLocalError`.
.. opcode:: LOAD_FAST_CHECK (var_num)
Pushes a reference to the local ``co_varnames[var_num]`` onto the stack,
raising an :exc:`UnboundLocalError` if the local variable has not been
initialized.
.. versionadded:: 3.12
.. opcode:: STORE_FAST (var_num)
Stores ``STACK.pop()`` 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 empty 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 ``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 ``STACK.pop()`` into the cell contained in slot ``i`` of the "fast locals"
storage.
.. versionchanged:: 3.11
``i`` is no longer offset by the length of ``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 ``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 STACK[-1]`` (raise exception instance or type at ``STACK[-1]``)
* 2: ``raise STACK[-2] from STACK[-1]`` (raise exception instance or type at
``STACK[-2]`` with ``__cause__`` set to ``STACK[-1]``)
.. 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:: 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 (consti)
Prefixes :opcode:`CALL`.
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 ``STACK[-2]``)
* the :term:`qualified name` of the function (at ``STACK[-1]``)
.. versionchanged:: 3.10
Flag value ``0x04`` is a tuple of strings instead of dictionary
.. opcode:: BUILD_SLICE (argc)
.. index:: builtin: slice
Pushes a slice object on the stack. *argc* must be 2 or 3. If it is 2, implements::
end = STACK.pop()
start = STACK.pop()
STACK.append(slice(start, stop))
if it is 3, implements::
step = STACK.pop()
end = STACK.pop()
start = STACK.pop()
STACK.append(slice(start, end, step))
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)
``STACK[-1]`` is a tuple of keyword attribute names, ``STACK[-2]`` is the class
being matched against, and ``STACK[-3]`` is the match subject. *count* is the
number of positional sub-patterns.
Pop ``STACK[-1]``, ``STACK[-2]``, and ``STACK[-3]``. If ``STACK[-3]`` is an
instance of ``STACK[-2]`` and has the positional and keyword attributes
required by *count* and ``STACK[-1]``, 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, which is neither a generator, coroutine
nor an async generator
* ``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.
Used as first opcode of in code object for the above mentioned callables.
Clear the current frame and return the newly created generator.
.. versionadded:: 3.11
.. opcode:: SEND (delta)
Equivalent to ``STACK[-1] = STACK[-2].send(STACK[-1])``. Used in ``yield from``
and ``await`` statements.
If the call raises :exc:`StopIteration`, pop both items, push the
exception's ``value`` attribute, and increment the bytecode counter by
*delta*.
.. versionadded:: 3.11
.. opcode:: HAVE_ARGUMENT
This is not really an opcode. It identifies the dividing line between
opcodes in the range [0,255] which don't use their argument and those
that do (``< HAVE_ARGUMENT`` and ``>= HAVE_ARGUMENT``, respectively).
If your application uses pseudo instructions, use the :data:`hasarg`
collection instead.
.. versionchanged:: 3.6
Now every instruction has an argument, but opcodes ``< HAVE_ARGUMENT``
ignore it. Before, only opcodes ``>= HAVE_ARGUMENT`` had an argument.
.. versionchanged:: 3.12
Pseudo instructions were added to the :mod:`dis` module, and for them
it is not true that comparison with ``HAVE_ARGUMENT`` indicates whether
they use their arg.
.. opcode:: CALL_INTRINSIC_1
Calls an intrinsic function with one argument. Passes ``STACK[-1]`` as the
argument and sets ``STACK[-1]`` to the result. Used to implement
functionality that is necessary but not performance critical.
The operand determines which intrinsic function is called:
* ``0`` Not valid
* ``1`` Prints the argument to standard out. Used in the REPL.
* ``2`` Performs ``import *`` for the named module.
* ``3`` Extracts the return value from a ``StopIteration`` exception.
* ``4`` Wraps an aync generator value
* ``5`` Performs the unary ``+`` operation
* ``6`` Converts a list to a tuple
.. versionadded:: 3.12
.. opcode:: CALL_INTRINSIC_2
Calls an intrinsic function with two arguments. Passes ``STACK[-2]``, ``STACK[-1]`` as the
arguments and sets ``STACK[-1]`` to the result. Used to implement functionality that is
necessary but not performance critical.
The operand determines which intrinsic function is called:
* ``0`` Not valid
* ``1`` Calculates the :exc:`ExceptionGroup` to raise from a ``try-except*``.
.. versionadded:: 3.12
**Pseudo-instructions**
These opcodes do not appear in python bytecode, they are used by the compiler
but are replaced by real opcodes or removed before bytecode is generated.
.. opcode:: SETUP_FINALLY (target)
Set up an exception handler for the following code block. If an exception
occurs, the value stack level is restored to its current state and control
is transferred to the exception handler at ``target``.
.. opcode:: SETUP_CLEANUP (target)
Like ``SETUP_FINALLY``, but in case of exception also pushes the last
instruction (``lasti``) to the stack so that ``RERAISE`` can restore it.
If an exception occurs, the value stack level and the last instruction on
the frame are restored to their current state, and control is transferred
to the exception handler at ``target``.
.. opcode:: SETUP_WITH (target)
Like ``SETUP_CLEANUP``, but in case of exception one more item is popped
from the stack before control is transferred to the exception handler at
``target``.
This variant is used in :keyword:`with` and :keyword:`async with`
constructs, which push the return value of the context manager's
:meth:`~object.__enter__` or :meth:`~object.__aenter__` to the stack.
.. opcode:: POP_BLOCK
Marks the end of the code block associated with the last ``SETUP_FINALLY``,
``SETUP_CLEANUP`` or ``SETUP_WITH``.
.. opcode:: JUMP
.. opcode:: JUMP_NO_INTERRUPT
Undirected relative jump instructions which are replaced by their
directed (forward/backward) counterparts by the assembler.
.. opcode:: LOAD_METHOD
Optimized unbound method lookup. Emitted as a ``LOAD_ATTR`` opcode
with a flag set in the arg.
.. _opcode_collections:
Opcode collections
------------------
These collections are provided for automatic introspection of bytecode
instructions:
.. versionchanged:: 3.12
The collections now contain pseudo instructions as well. These are
opcodes with values ``>= MIN_PSEUDO_OPCODE``.
.. 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:: hasarg
Sequence of bytecodes that use their argument.
.. versionadded:: 3.12
.. 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.
.. data:: hasexc
Sequence of bytecodes that set an exception handler.
.. versionadded:: 3.12
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