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cpython/Doc/library/dis.rst
Irit Katriel dea5bf9d15
bpo-33387: update documentation for exception handling opcode changes (GH-24334) 
* bpo-33387: remove obsolete comment

* bpo-33387: update SETUP_WITH opcode documentation
2021-01-26 10:17:13 +00:00

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:mod:`dis` --- Disassembler for Python bytecode
===============================================
.. module:: dis
:synopsis: Disassembler for Python bytecode.
**Source code:** :source:`Lib/dis.py`
--------------
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.
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`::
>>> dis.dis(myfunc)
2 0 LOAD_GLOBAL 0 (len)
2 LOAD_FAST 0 (alist)
4 CALL_FUNCTION 1
6 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)
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.
.. classmethod:: from_traceback(tb)
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.
Example::
>>> bytecode = dis.Bytecode(myfunc)
>>> for instr in bytecode:
... print(instr.opname)
...
LOAD_GLOBAL
LOAD_FAST
CALL_FUNCTION
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)
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.
.. 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.
.. function:: distb(tb=None, *, file=None)
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.
.. function:: disassemble(code, lasti=-1, *, file=None)
disco(code, lasti=-1, *, file=None)
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.
.. function:: get_instructions(x, *, first_line=None)
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.
.. versionadded:: 3.4
.. function:: findlinestarts(code)
This generator function uses the ``co_firstlineno`` and ``co_lnotab``
attributes 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.
See :source:`Objects/lnotab_notes.txt` for the ``co_lnotab`` format and
how to decode it.
.. versionchanged:: 3.6
Line numbers can be decreasing. Before, they were always increasing.
.. 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 known), otherwise same as arg
.. data:: argrepr
human readable description of operation argument
.. 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``
.. versionadded:: 3.4
The Python compiler currently generates the following bytecode instructions.
**General instructions**
.. opcode:: NOP
Do nothing code. Used as a placeholder by the bytecode optimizer.
.. opcode:: POP_TOP
Removes the top-of-stack (TOS) item.
.. opcode:: ROT_TWO
Swaps the two top-most stack items.
.. opcode:: ROT_THREE
Lifts second and third stack item one position up, moves top down to position
three.
.. opcode:: ROT_FOUR
Lifts second, third and forth stack items one position up, moves top down
to position four.
.. versionadded:: 3.8
.. opcode:: DUP_TOP
Duplicates the reference on top of the stack.
.. versionadded:: 3.2
.. opcode:: DUP_TOP_TWO
Duplicates the two references on top of the stack, leaving them in the
same order.
.. versionadded:: 3.2
**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 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.
.. opcode:: BINARY_POWER
Implements ``TOS = TOS1 ** TOS``.
.. opcode:: BINARY_MULTIPLY
Implements ``TOS = TOS1 * TOS``.
.. opcode:: BINARY_MATRIX_MULTIPLY
Implements ``TOS = TOS1 @ TOS``.
.. versionadded:: 3.5
.. opcode:: BINARY_FLOOR_DIVIDE
Implements ``TOS = TOS1 // TOS``.
.. opcode:: BINARY_TRUE_DIVIDE
Implements ``TOS = TOS1 / TOS``.
.. opcode:: BINARY_MODULO
Implements ``TOS = TOS1 % TOS``.
.. opcode:: BINARY_ADD
Implements ``TOS = TOS1 + TOS``.
.. opcode:: BINARY_SUBTRACT
Implements ``TOS = TOS1 - TOS``.
.. opcode:: BINARY_SUBSCR
Implements ``TOS = TOS1[TOS]``.
.. opcode:: BINARY_LSHIFT
Implements ``TOS = TOS1 << TOS``.
.. opcode:: BINARY_RSHIFT
Implements ``TOS = TOS1 >> TOS``.
.. opcode:: BINARY_AND
Implements ``TOS = TOS1 & TOS``.
.. opcode:: BINARY_XOR
Implements ``TOS = TOS1 ^ TOS``.
.. opcode:: BINARY_OR
Implements ``TOS = TOS1 | TOS``.
**In-place operations**
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:: INPLACE_POWER
Implements in-place ``TOS = TOS1 ** TOS``.
.. opcode:: INPLACE_MULTIPLY
Implements in-place ``TOS = TOS1 * TOS``.
.. opcode:: INPLACE_MATRIX_MULTIPLY
Implements in-place ``TOS = TOS1 @ TOS``.
.. versionadded:: 3.5
.. opcode:: INPLACE_FLOOR_DIVIDE
Implements in-place ``TOS = TOS1 // TOS``.
.. opcode:: INPLACE_TRUE_DIVIDE
Implements in-place ``TOS = TOS1 / TOS``.
.. opcode:: INPLACE_MODULO
Implements in-place ``TOS = TOS1 % TOS``.
.. opcode:: INPLACE_ADD
Implements in-place ``TOS = TOS1 + TOS``.
.. opcode:: INPLACE_SUBTRACT
Implements in-place ``TOS = TOS1 - TOS``.
.. opcode:: INPLACE_LSHIFT
Implements in-place ``TOS = TOS1 << TOS``.
.. opcode:: INPLACE_RSHIFT
Implements in-place ``TOS = TOS1 >> TOS``.
.. opcode:: INPLACE_AND
Implements in-place ``TOS = TOS1 & TOS``.
.. opcode:: INPLACE_XOR
Implements in-place ``TOS = TOS1 ^ TOS``.
.. opcode:: INPLACE_OR
Implements in-place ``TOS = TOS1 | TOS``.
.. opcode:: STORE_SUBSCR
Implements ``TOS1[TOS] = TOS2``.
.. opcode:: DELETE_SUBSCR
Implements ``del TOS1[TOS]``.
**Coroutine opcodes**
.. opcode:: GET_AWAITABLE
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__``.
.. versionadded:: 3.5
.. 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
Implements ``PUSH(get_awaitable(TOS.__anext__()))``. 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. If TOS is :exc:`StopAsyncIteration` pop 7
values from the stack and restore the exception state using the second
three of them. Otherwise re-raise the exception using the three values
from the stack. An exception handler block is removed from the block stack.
.. versionadded:: 3.8
.. 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
.. opcode:: SETUP_ASYNC_WITH
Creates a new frame object.
.. 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:: YIELD_FROM
Pops TOS and delegates to it as a subiterator from a :term:`generator`.
.. versionadded:: 3.3
.. 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_BLOCK
Removes one block from the block stack. Per frame, there is a stack of
blocks, denoting :keyword:`try` statements, and such.
.. opcode:: POP_EXCEPT
Removes one block from the block stack. The popped block must be an exception
handler block, as implicitly created when entering an except handler. In
addition to popping extraneous values from the frame stack, the last three
popped values are used to restore the exception state.
.. opcode:: RERAISE
Re-raises the exception currently on top of the stack. If oparg is non-zero,
restores ``f_lasti`` of the current frame to its value when the exception was raised.
.. versionadded:: 3.9
.. opcode:: WITH_EXCEPT_START
Calls the function in position 7 on the stack with the top three
items on the stack as arguments.
Used to implement the call ``context_manager.__exit__(*exc_info())`` when an exception
has occurred in a :keyword:`with` statement.
.. versionadded:: 3.9
.. 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
by :opcode:`CALL_FUNCTION` to construct a class.
.. opcode:: SETUP_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, and a finally block pointing to *delta*
is pushed. Finally, the result of calling the ``__enter__()`` method is pushed onto
the stack. The next opcode will either ignore it (:opcode:`POP_TOP`), or
store it in (a) variable(s) (:opcode:`STORE_FAST`, :opcode:`STORE_NAME`, or
:opcode:`UNPACK_SEQUENCE`).
.. versionadded:: 3.2
All of the following opcodes use their arguments.
.. opcode:: STORE_NAME (namei)
Implements ``name = TOS``. *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 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:`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.
.. 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
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:: POP_JUMP_IF_TRUE (target)
If TOS is true, sets the bytecode counter to *target*. TOS is popped.
.. versionadded:: 3.1
.. opcode:: POP_JUMP_IF_FALSE (target)
If TOS is false, sets the bytecode counter to *target*. TOS is popped.
.. versionadded:: 3.1
.. opcode:: JUMP_IF_NOT_EXC_MATCH (target)
Tests whether the second value on the stack is an exception matching TOS,
and jumps if it is not. Pops two values from the stack.
.. versionadded:: 3.9
.. opcode:: JUMP_IF_TRUE_OR_POP (target)
If TOS is true, sets the bytecode counter to *target* and leaves TOS on the
stack. Otherwise (TOS is false), TOS is popped.
.. versionadded:: 3.1
.. opcode:: JUMP_IF_FALSE_OR_POP (target)
If TOS is false, sets the bytecode counter to *target* and leaves TOS on the
stack. Otherwise (TOS is true), TOS is popped.
.. versionadded:: 3.1
.. opcode:: JUMP_ABSOLUTE (target)
Set bytecode counter to *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]`` onto the stack.
.. opcode:: SETUP_FINALLY (delta)
Pushes a try block from a try-finally or try-except clause onto the block
stack. *delta* points to the finally block or the first except block.
.. 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:: LOAD_CLOSURE (i)
Pushes a reference to the cell contained in slot *i* of the cell and free
variable storage. The name of the variable is ``co_cellvars[i]`` if *i* is
less than the length of *co_cellvars*. Otherwise it is ``co_freevars[i -
len(co_cellvars)]``.
.. opcode:: LOAD_DEREF (i)
Loads the cell contained in slot *i* of the cell and free variable storage.
Pushes a reference to the object the cell contains on the stack.
.. 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
.. opcode:: STORE_DEREF (i)
Stores TOS into the cell contained in slot *i* of the cell and free variable
storage.
.. opcode:: DELETE_DEREF (i)
Empties the cell contained in slot *i* of the cell and free variable storage.
Used by the :keyword:`del` statement.
.. versionadded:: 3.2
.. 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_FUNCTION (argc)
Calls a callable object with positional arguments.
*argc* indicates the number of positional arguments.
The top of the stack contains positional arguments, with the right-most
argument on top. Below the arguments is a callable object to call.
``CALL_FUNCTION`` 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.
.. versionchanged:: 3.6
This opcode is used only for calls with positional arguments.
.. opcode:: CALL_FUNCTION_KW (argc)
Calls a callable object with positional (if any) and keyword arguments.
*argc* indicates the total number of positional and keyword arguments.
The top element on the stack contains a tuple with the names of the
keyword arguments, which must be strings.
Below that are the values for the keyword arguments,
in the order corresponding to the tuple.
Below that are positional arguments, with the right-most parameter on
top. Below the arguments is a callable object to call.
``CALL_FUNCTION_KW`` 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.
.. versionchanged:: 3.6
Keyword arguments are packed in a tuple instead of a dictionary,
*argc* indicates the total number of arguments.
.. 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_METHOD` when calling the
unbound method. Otherwise, ``NULL`` and the object return by the attribute
lookup are pushed.
.. versionadded:: 3.7
.. opcode:: CALL_METHOD (argc)
Calls a method. *argc* is the number of positional arguments.
Keyword arguments are not supported. This opcode is designed to be used
with :opcode:`LOAD_METHOD`. Positional arguments are on top of the stack.
Below them, the two items described in :opcode:`LOAD_METHOD` are on the
stack (either ``self`` and an unbound method object or ``NULL`` and an
arbitrary callable). All of them are popped and the return value is pushed.
.. versionadded:: 3.7
.. 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 TOS1)
* the :term:`qualified name` of the function (at TOS)
.. 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,
``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:: 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.
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