dis — Disassembler for Python bytecode

Source code: Lib/dis.py


The dis module supports the analysis of CPython bytecode by disassembling it. The CPython bytecode which this module takes as an input is defined in the file Include/opcode.h and used by the compiler and the interpreter.

CPython implementation 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.

Changed in version 3.6: Use 2 bytes for each instruction. Previously the number of bytes varied by instruction.

Changed in version 3.10: The argument of jump, exception handling and loop instructions is now the instruction offset rather than the byte offset.

Changed in version 3.11: Some instructions are accompanied by one or more inline cache entries, which take the form of CACHE instructions. These instructions are hidden by default, but can be shown by passing show_caches=True to any 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 myfunc():

def myfunc(alist):
    return len(alist)

the following command can be used to display the disassembly of myfunc():

>>> dis.dis(myfunc)
  2           0 RESUME                   0

  3           2 LOAD_GLOBAL              1 (len + NULL)
             12 LOAD_FAST                0 (alist)
             14 CALL                     1
             22 RETURN_VALUE

(The “2” is a line number).

Bytecode analysis

New in version 3.4.

The bytecode analysis API allows pieces of Python code to be wrapped in a Bytecode object that provides easy access to details of the compiled code.

class dis.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 compile()).

This is a convenience wrapper around many of the functions listed below, most notably get_instructions(), as iterating over a Bytecode instance yields the bytecode operations as 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 dis() will display a “current instruction” marker against the specified opcode.

If show_caches is True, dis() will display inline cache entries used by the interpreter to specialize the bytecode.

If adaptive is True, dis() will display specialized bytecode that may be different from the original bytecode.

classmethod from_traceback(tb, *, show_caches=False)

Construct a Bytecode instance from the given traceback, setting current_offset to the instruction responsible for the exception.

codeobj

The compiled code object.

first_line

The first source line of the code object (if available)

dis()

Return a formatted view of the bytecode operations (the same as printed by dis.dis(), but returned as a multi-line string).

info()

Return a formatted multi-line string with detailed information about the code object, like code_info().

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

Changed in version 3.11: Added the show_caches and adaptive parameters.

Example:

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

Analysis functions

The 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:

dis.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.

New in version 3.2.

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

dis.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.

New in version 3.2.

Changed in version 3.4: Added file parameter.

dis.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. These can include generator expressions, nested functions, the bodies of nested classes, and the code objects used for annotation scopes. Strings are first compiled to code objects with the 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.

Changed in version 3.4: Added file parameter.

Changed in version 3.7: Implemented recursive disassembling and added depth parameter.

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.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.

Changed in version 3.4: Added file parameter.

Changed in version 3.11: Added the show_caches and adaptive parameters.

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

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

  2. the current instruction, indicated as -->,

  3. a labelled instruction, indicated with >>,

  4. the address of the instruction,

  5. the operation code name,

  6. operation parameters, and

  7. 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.

Changed in version 3.4: Added file parameter.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.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 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 dis().

New in version 3.4.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.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.

Changed in version 3.6: Line numbers can be decreasing. Before, they were always increasing.

Changed in version 3.10: The PEP 626 co_lines method is used instead of the co_firstlineno and co_lnotab attributes of the code object.

Changed in version 3.13: Line numbers can be None for bytecode that does not map to source lines.

dis.findlabels(code)

Detect all offsets in the raw compiled bytecode string code which are jump targets, and return a list of these offsets.

dis.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, 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.

New in version 3.4.

Changed in version 3.8: Added jump parameter.

Changed in version 3.13: If oparg is omitted (or None), the stack effect is now returned for oparg=0. Previously this was an error for opcodes that use their arg. It is also no longer an error to pass an integer oparg when the opcode does not use it; the oparg in this case is ignored.

Python Bytecode Instructions

The get_instructions() function and Bytecode class provide details of bytecode instructions as Instruction instances:

class dis.Instruction

Details for a bytecode operation

opcode

numeric code for operation, corresponding to the opcode values listed below and the bytecode values in the Opcode collections.

opname

human readable name for operation

baseopcode

numeric code for the base operation if operation is specialized; otherwise equal to opcode

baseopname

human readable name for the base operation if operation is specialized; otherwise equal to opname

arg

numeric argument to operation (if any), otherwise None

oparg

alias for arg

argval

resolved arg value (if any), otherwise None

argrepr

human readable description of operation argument (if any), otherwise an empty string.

offset

start index of operation within bytecode sequence

start_offset

start index of operation within bytecode sequence, including prefixed EXTENDED_ARG operations if present; otherwise equal to offset

cache_offset

start index of the cache entries following the operation

end_offset

end index of the cache entries following the operation

starts_line

True if this opcode starts a source line, otherwise False

line_number

source line number associated with this opcode (if any), otherwise None

is_jump_target

True if other code jumps to here, otherwise False

jump_target

bytecode index of the jump target if this is a jump operation, otherwise None

positions

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

New in version 3.4.

Changed in version 3.11: Field positions is added.

Changed in version 3.13: Changed field starts_line.

Added fields start_offset, cache_offset, end_offset, baseopname, baseopcode, jump_target, oparg, and line_number.

class dis.Positions

In case the information is not available, some fields might be None.

lineno
end_lineno
col_offset
end_col_offset

New in version 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.

NOP

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

POP_TOP

Removes the top-of-stack item:

STACK.pop()
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.

New in version 3.12.

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])

New in version 3.11.

SWAP(i)

Swap the top of the stack with the i-th element:

STACK[-i], STACK[-1] = stack[-1], STACK[-i]

New in version 3.11.

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.

New in version 3.11.

Unary operations

Unary operations take the top of the stack, apply the operation, and push the result back on the stack.

UNARY_NEGATIVE

Implements STACK[-1] = -STACK[-1].

UNARY_NOT

Implements STACK[-1] = not STACK[-1].

Changed in version 3.13: This instruction now requires an exact bool operand.

UNARY_INVERT

Implements STACK[-1] = ~STACK[-1].

GET_ITER

Implements STACK[-1] = iter(STACK[-1]).

GET_YIELD_FROM_ITER

If STACK[-1] is a generator iterator or coroutine object it is left as is. Otherwise, implements STACK[-1] = iter(STACK[-1]).

New in version 3.5.

TO_BOOL

Implements STACK[-1] = bool(STACK[-1]).

New in version 3.13.

Binary and in-place operations

Binary operations remove the top two items from the stack (STACK[-1] and STACK[-2]). They perform the operation, then put the result back on the stack.

In-place operations are like binary operations, but the operation is done in-place when STACK[-2] supports it, and the resulting STACK[-1] may be (but does not have to be) the original STACK[-2].

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)

New in version 3.11.

BINARY_SUBSCR

Implements:

key = STACK.pop()
container = STACK.pop()
STACK.append(container[key])
STORE_SUBSCR

Implements:

key = STACK.pop()
container = STACK.pop()
value = STACK.pop()
container[key] = value
DELETE_SUBSCR

Implements:

key = STACK.pop()
container = STACK.pop()
del container[key]
BINARY_SLICE

Implements:

end = STACK.pop()
start = STACK.pop()
container = STACK.pop()
STACK.append(container[start:end])

New in version 3.12.

STORE_SLICE

Implements:

end = STACK.pop()
start = STACK.pop()
container = STACK.pop()
values = STACK.pop()
container[start:end] = value

New in version 3.12.

Coroutine opcodes

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__

New in version 3.5.

Changed in version 3.11: Previously, this instruction did not have an oparg.

GET_AITER

Implements STACK[-1] = STACK[-1].__aiter__().

New in version 3.5.

Changed in version 3.7: Returning awaitable objects from __aiter__ is no longer supported.

GET_ANEXT

Implement STACK.append(get_awaitable(STACK[-1].__anext__())) to the stack. See GET_AWAITABLE for details about get_awaitable.

New in version 3.5.

END_ASYNC_FOR

Terminates an 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 StopAsyncIteration, it is re-raised.

New in version 3.8.

Changed in version 3.11: Exception representation on the stack now consist of one, not three, items.

CLEANUP_THROW

Handles an exception raised during a throw() or close() call through the current frame. If STACK[-1] is an instance of StopIteration, pop three values from the stack and push its value member. Otherwise, re-raise STACK[-1].

New in version 3.12.

BEFORE_ASYNC_WITH

Resolves __aenter__ and __aexit__ from STACK[-1]. Pushes __aexit__ and result of __aenter__() to the stack:

STACK.extend((__aexit__, __aenter__())

New in version 3.5.

Miscellaneous opcodes

SET_ADD(i)

Implements:

item = STACK.pop()
set.add(STACK[-i], item)

Used to implement set comprehensions.

LIST_APPEND(i)

Implements:

item = STACK.pop()
list.append(STACK[-i], item)

Used to implement list comprehensions.

MAP_ADD(i)

Implements:

value = STACK.pop()
key = STACK.pop()
dict.__setitem__(STACK[-i], key, value)

Used to implement dict comprehensions.

New in version 3.1.

Changed in version 3.8: Map value is STACK[-1] and map key is STACK[-2]. Before, those were reversed.

For all of the SET_ADD, LIST_APPEND and 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.

RETURN_VALUE

Returns with STACK[-1] to the caller of the function.

RETURN_CONST(consti)

Returns with co_consts[consti] to the caller of the function.

New in version 3.12.

YIELD_VALUE

Yields STACK.pop() from a generator.

Changed in version 3.11: oparg set to be the stack depth.

Changed in version 3.12: oparg set to be the exception block depth, for efficient closing of generators.

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 variable annotations statically.

New in version 3.6.

POP_EXCEPT

Pops a value from the stack, which is used to restore the exception state.

Changed in version 3.11: Exception representation on the stack now consist of one, not three, items.

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.

New in version 3.9.

Changed in version 3.11: Exception representation on the stack now consist of one, not three, items.

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.

New in version 3.11.

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.

New in version 3.11.

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.

New in version 3.11.

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 with statement.

New in version 3.9.

Changed in version 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.

LOAD_ASSERTION_ERROR

Pushes AssertionError onto the stack. Used by the assert statement.

New in version 3.9.

LOAD_BUILD_CLASS

Pushes builtins.__build_class__() onto the stack. It is later called to construct a class.

BEFORE_WITH

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

New in version 3.11.

GET_LEN

Perform STACK.append(len(STACK[-1])).

New in version 3.10.

MATCH_MAPPING

If STACK[-1] is an instance of collections.abc.Mapping (or, more technically: if it has the Py_TPFLAGS_MAPPING flag set in its tp_flags), push True onto the stack. Otherwise, push False.

New in version 3.10.

MATCH_SEQUENCE

If STACK[-1] is an instance of collections.abc.Sequence and is not an instance of str/bytes/bytearray (or, more technically: if it has the Py_TPFLAGS_SEQUENCE flag set in its tp_flags), push True onto the stack. Otherwise, push False.

New in version 3.10.

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 tuple containing the corresponding values. Otherwise, push None.

New in version 3.10.

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

STORE_NAME(namei)

Implements name = STACK.pop(). namei is the index of name in the attribute co_names of the code object. The compiler tries to use STORE_FAST or STORE_GLOBAL if possible.

DELETE_NAME(namei)

Implements del name, where namei is the index into co_names attribute of the code object.

UNPACK_SEQUENCE(count)

Unpacks STACK[-1] into count individual values, which are put onto the stack right-to-left. Require there to be exactly count values.:

assert(len(STACK[-1]) == count)
STACK.extend(STACK.pop()[:-count-1:-1])
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)).

STORE_ATTR(namei)

Implements:

obj = STACK.pop()
value = STACK.pop()
obj.name = value

where namei is the index of name in co_names of the code object.

DELETE_ATTR(namei)

Implements:

obj = STACK.pop()
del obj.name

where namei is the index of name into co_names of the code object.

STORE_GLOBAL(namei)

Works as STORE_NAME, but stores the name as a global.

DELETE_GLOBAL(namei)

Works as DELETE_NAME, but deletes a global name.

LOAD_CONST(consti)

Pushes co_consts[consti] onto the stack.

LOAD_NAME(namei)

Pushes the value associated with co_names[namei] onto the stack. The name is looked up within the locals, then the globals, then the builtins.

LOAD_LOCALS

Pushes a reference to the locals dictionary onto the stack. This is used to prepare namespace dictionaries for LOAD_FROM_DICT_OR_DEREF and LOAD_FROM_DICT_OR_GLOBALS.

New in version 3.12.

LOAD_FROM_DICT_OR_GLOBALS(i)

Pops a mapping off the stack and looks up the value for co_names[namei]. If the name is not found there, looks it up in the globals and then the builtins, similar to LOAD_GLOBAL. This is used for loading global variables in annotation scopes within class bodies.

New in version 3.12.

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))
BUILD_LIST(count)

Works as BUILD_TUPLE, but creates a list.

BUILD_SET(count)

Works as BUILD_TUPLE, but creates a set.

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]}.

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

BUILD_CONST_KEY_MAP(count)

The version of 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.

New in version 3.6.

BUILD_STRING(count)

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

New in version 3.6.

LIST_EXTEND(i)

Implements:

seq = STACK.pop()
list.extend(STACK[-i], seq)

Used to build lists.

New in version 3.9.

SET_UPDATE(i)

Implements:

seq = STACK.pop()
set.update(STACK[-i], seq)

Used to build sets.

New in version 3.9.

DICT_UPDATE(i)

Implements:

map = STACK.pop()
dict.update(STACK[-i], map)

Used to build dicts.

New in version 3.9.

DICT_MERGE(i)

Like DICT_UPDATE but raises an exception for duplicate keys.

New in version 3.9.

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 CALL or CALL_KW when calling the unbound method. Otherwise, NULL and the object returned by the attribute lookup are pushed.

Changed in version 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.

LOAD_SUPER_ATTR(namei)

This opcode implements super() (e.g. super().method() and super().attr). It works the same as LOAD_ATTR, except that namei is shifted left by 2 bits instead of 1, and instead of expecting a single receiver on the stack, it expects three objects (from top of stack down): self (the first argument to the current method), cls (the class within which the current method was defined), and the global super.

The low bit of namei signals to attempt a method load, as with LOAD_ATTR.

The second-low bit of namei, if set, means that this was a two-argument call to super() (unset means zero-argument).

New in version 3.12.

COMPARE_OP(opname)

Performs a Boolean operation. The operation name can be found in cmp_op[opname >> 5]. If the fifth-lowest bit of opname is set (opname & 16), the result should be coerced to bool.

Changed in version 3.13: The fifth-lowest bit of the oparg now indicates a forced conversion to bool.

IS_OP(invert)

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

New in version 3.9.

CONTAINS_OP(invert)

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

New in version 3.9.

IMPORT_NAME(namei)

Imports the module co_names[namei]. STACK[-1] and STACK[-2] are popped and provide the fromlist and level arguments of __import__(). The module object is pushed onto the stack. The current namespace is not affected: for a proper import statement, a subsequent STORE_FAST instruction modifies the namespace.

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 STORE_FAST instruction.

JUMP_FORWARD(delta)

Increments bytecode counter by delta.

JUMP_BACKWARD(delta)

Decrements bytecode counter by delta. Checks for interrupts.

New in version 3.11.

JUMP_BACKWARD_NO_INTERRUPT(delta)

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

New in version 3.11.

POP_JUMP_IF_TRUE(delta)

If STACK[-1] is true, increments the bytecode counter by delta. STACK[-1] is popped.

Changed in version 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).

Changed in version 3.12: This is no longer a pseudo-instruction.

Changed in version 3.13: This instruction now requires an exact bool operand.

POP_JUMP_IF_FALSE(delta)

If STACK[-1] is false, increments the bytecode counter by delta. STACK[-1] is popped.

Changed in version 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).

Changed in version 3.12: This is no longer a pseudo-instruction.

Changed in version 3.13: This instruction now requires an exact bool operand.

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).

New in version 3.11.

Changed in version 3.12: This is no longer a pseudo-instruction.

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).

New in version 3.11.

Changed in version 3.12: This is no longer a pseudo-instruction.

FOR_ITER(delta)

STACK[-1] is an iterator. Call its __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.

Changed in version 3.12: Up until 3.11 the iterator was popped when it was exhausted.

LOAD_GLOBAL(namei)

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

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

LOAD_FAST(var_num)

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

Changed in version 3.12: This opcode is now only used in situations where the local variable is guaranteed to be initialized. It cannot raise UnboundLocalError.

LOAD_FAST_CHECK(var_num)

Pushes a reference to the local co_varnames[var_num] onto the stack, raising an UnboundLocalError if the local variable has not been initialized.

New in version 3.12.

LOAD_FAST_AND_CLEAR(var_num)

Pushes a reference to the local co_varnames[var_num] onto the stack (or pushes NULL onto the stack if the local variable has not been initialized) and sets co_varnames[var_num] to NULL.

New in version 3.12.

STORE_FAST(var_num)

Stores STACK.pop() into the local co_varnames[var_num].

DELETE_FAST(var_num)

Deletes local co_varnames[var_num].

MAKE_CELL(i)

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

New in version 3.11.

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.

Changed in version 3.11: i is no longer offset by the length of co_varnames.

LOAD_FROM_DICT_OR_DEREF(i)

Pops a mapping off the stack and looks up the name associated with slot i of the “fast locals” storage in this mapping. If the name is not found there, loads it from the cell contained in slot i, similar to LOAD_DEREF. This is used for loading free variables in class bodies (which previously used LOAD_CLASSDEREF) and in annotation scopes within class bodies.

New in version 3.12.

STORE_DEREF(i)

Stores STACK.pop() into the cell contained in slot i of the “fast locals” storage.

Changed in version 3.11: i is no longer offset by the length of co_varnames.

DELETE_DEREF(i)

Empties the cell contained in slot i of the “fast locals” storage. Used by the del statement.

New in version 3.2.

Changed in version 3.11: i is no longer offset by the length of co_varnames.

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.

New in version 3.11.

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])

CALL(argc)

Calls a callable object with the number of arguments specified by argc. On the stack are (in ascending order):

  • The callable

  • self or NULL

  • The remaining positional arguments

argc is the total of the positional arguments, excluding self.

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.

New in version 3.11.

Changed in version 3.13: The callable now always appears at the same position on the stack.

Changed in version 3.13: Calls with keyword arguments are now handled by CALL_KW.

CALL_KW(argc)

Calls a callable object with the number of arguments specified by argc, including one or more named arguments. On the stack are (in ascending order):

  • The callable

  • self or NULL

  • The remaining positional arguments

  • The named arguments

  • A tuple of keyword argument names

argc is the total of the positional and named arguments, excluding self. The length of the tuple of keyword argument names is the number of named arguments.

CALL_KW pops all arguments, the keyword names, and the callable object off the stack, calls the callable object with those arguments, and pushes the return value returned by the callable object.

New in version 3.13.

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.

New in version 3.6.

PUSH_NULL

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

New in version 3.11.

MAKE_FUNCTION

Pushes a new function object on the stack built from the code object at STACK[1].

Changed in version 3.10: Flag value 0x04 is a tuple of strings instead of dictionary

Changed in version 3.11: Qualified name at STACK[-1] was removed.

Changed in version 3.13: Extra function attributes on the stack, signaled by oparg flags, were removed. They now use SET_FUNCTION_ATTRIBUTE.

SET_FUNCTION_ATTRIBUTE(flag)

Sets an attribute on a function object. Expects the function at STACK[-1] and the attribute value to set at STACK[-2]; consumes both and leaves the function at STACK[-1]. The flag determines which attribute to set:

  • 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

New in version 3.13.

BUILD_SLICE(argc)

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 slice() built-in function for more information.

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.

CONVERT_VALUE(oparg)

Convert value to a string, depending on oparg:

value = STACK.pop()
result = func(value)
STACK.push(result)
  • oparg == 1: call str() on value

  • oparg == 2: call repr() on value

  • oparg == 3: call ascii() on value

Used for implementing formatted literal strings (f-strings).

New in version 3.13.

FORMAT_SIMPLE

Formats the value on top of stack:

value = STACK.pop()
result = value.__format__("")
STACK.push(result)

Used for implementing formatted literal strings (f-strings).

New in version 3.13.

FORMAT_SPEC

Formats the given value with the given format spec:

spec = STACK.pop()
value = STACK.pop()
result = value.__format__(spec)
STACK.push(result)

Used for implementing formatted literal strings (f-strings).

New in version 3.13.

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.

New in version 3.10.

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

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

New in version 3.11.

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.

New in version 3.11.

SEND(delta)

Equivalent to STACK[-1] = STACK[-2].send(STACK[-1]). Used in yield from and await statements.

If the call raises StopIteration, pop both items, push the exception’s value attribute, and increment the bytecode counter by delta.

New in version 3.11.

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 or specialized instructions, use the hasarg collection instead.

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

Changed in version 3.12: Pseudo instructions were added to the dis module, and for them it is not true that comparison with HAVE_ARGUMENT indicates whether they use their arg.

Deprecated since version 3.13: Use hasarg instead.

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:

Operand

Description

INTRINSIC_1_INVALID

Not valid

INTRINSIC_PRINT

Prints the argument to standard out. Used in the REPL.

INTRINSIC_IMPORT_STAR

Performs import * for the named module.

INTRINSIC_STOPITERATION_ERROR

Extracts the return value from a StopIteration exception.

INTRINSIC_ASYNC_GEN_WRAP

Wraps an aync generator value

INTRINSIC_UNARY_POSITIVE

Performs the unary + operation

INTRINSIC_LIST_TO_TUPLE

Converts a list to a tuple

INTRINSIC_TYPEVAR

Creates a typing.TypeVar

INTRINSIC_PARAMSPEC

Creates a typing.ParamSpec

INTRINSIC_TYPEVARTUPLE

Creates a typing.TypeVarTuple

INTRINSIC_SUBSCRIPT_GENERIC

Returns typing.Generic subscripted with the argument

INTRINSIC_TYPEALIAS

Creates a typing.TypeAliasType; used in the type statement. The argument is a tuple of the type alias’s name, type parameters, and value.

New in version 3.12.

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:

Operand

Description

INTRINSIC_2_INVALID

Not valid

INTRINSIC_PREP_RERAISE_STAR

Calculates the ExceptionGroup to raise from a try-except*.

INTRINSIC_TYPEVAR_WITH_BOUND

Creates a typing.TypeVar with a bound.

INTRINSIC_TYPEVAR_WITH_CONSTRAINTS

Creates a typing.TypeVar with constraints.

INTRINSIC_SET_FUNCTION_TYPE_PARAMS

Sets the __type_params__ attribute of a function.

New in version 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.

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.

SETUP_CLEANUP(target)

Like SETUP_FINALLY, but in case of an 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.

SETUP_WITH(target)

Like SETUP_CLEANUP, but in case of an exception one more item is popped from the stack before control is transferred to the exception handler at target.

This variant is used in with and async with constructs, which push the return value of the context manager’s __enter__() or __aenter__() to the stack.

POP_BLOCK

Marks the end of the code block associated with the last SETUP_FINALLY, SETUP_CLEANUP or SETUP_WITH.

JUMP
JUMP_NO_INTERRUPT

Undirected relative jump instructions which are replaced by their directed (forward/backward) counterparts by the assembler.

LOAD_CLOSURE(i)

Pushes a reference to the cell contained in slot i of the “fast locals” storage.

Note that LOAD_CLOSURE is replaced with LOAD_FAST in the assembler.

Changed in version 3.13: This opcode is now a pseudo-instruction.

LOAD_METHOD

Optimized unbound method lookup. Emitted as a LOAD_ATTR opcode with a flag set in the arg.

Opcode collections

These collections are provided for automatic introspection of bytecode instructions:

Changed in version 3.12: The collections now contain pseudo instructions as well. These are opcodes with values >= MIN_PSEUDO_OPCODE.

dis.opname

Sequence of operation names, indexable using the bytecode.

dis.opmap

Dictionary mapping operation names to bytecodes.

dis.cmp_op

Sequence of all compare operation names.

dis.hasarg

Sequence of bytecodes that use their argument.

New in version 3.12.

dis.hasconst

Sequence of bytecodes that access a constant.

dis.hasfree

Sequence of bytecodes that access a free variable. ‘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.

dis.hasname

Sequence of bytecodes that access an attribute by name.

dis.hasjump

Sequence of bytecodes that have a jump target. All jumps are relative.

New in version 3.13.

dis.haslocal

Sequence of bytecodes that access a local variable.

dis.hascompare

Sequence of bytecodes of Boolean operations.

dis.hasexc

Sequence of bytecodes that set an exception handler.

New in version 3.12.

dis.hasjrel

Sequence of bytecodes that have a relative jump target.

Deprecated since version 3.13: All jumps are now relative. Use hasjump.

dis.hasjabs

Sequence of bytecodes that have an absolute jump target.

Deprecated since version 3.13: All jumps are now relative. This list is empty.