Python 3.6.5 Documentation >  "dis" — Disassembler for Python bytecode

"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.

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 LOAD_GLOBAL 0 (len)
2 LOAD_FAST 0 (alist)
4 CALL_FUNCTION 1
6 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)

Analyse the bytecode corresponding to a function, generator,
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.

classmethod from_traceback(tb)

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()".

Example:

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

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)

Disassemble the *x* object. *x* can denote either a module, a
class, a method, a function, a generator, 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. 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.

Changed in version 3.4: Added *file* parameter.

dis.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.

Changed in version 3.4: Added *file* parameter.

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

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.

dis.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 "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.

New in version 3.4.

dis.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 Objects/lnotab_notes.txt for the
"co_lnotab" format and how to decode it.

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

dis.findlabels(code)

Detect all offsets in the code object *code* which are jump
targets, and return a list of these offsets.

dis.stack_effect(opcode[, oparg])

Compute the stack effect of *opcode* with argument *oparg*.

New in version 3.4.

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

arg

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

argval

resolved arg value (if known), otherwise same as arg

argrepr

human readable description of operation argument

offset

start index of operation within bytecode sequence

starts_line

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

is_jump_target

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

New in version 3.4.

The Python compiler currently generates the following bytecode
instructions.

**General instructions**

NOP

Do nothing code. Used as a placeholder by the bytecode optimizer.

POP_TOP

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

ROT_TWO

Swaps the two top-most stack items.

ROT_THREE

Lifts second and third stack item one position up, moves top down
to position three.

DUP_TOP

Duplicates the reference on top of the stack.

New in version 3.2.

DUP_TOP_TWO

Duplicates the two references on top of the stack, leaving them in
the same order.

New in version 3.2.

**Unary operations**

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

UNARY_POSITIVE

Implements "TOS = +TOS".

UNARY_NEGATIVE

Implements "TOS = -TOS".

UNARY_NOT

Implements "TOS = not TOS".

UNARY_INVERT

Implements "TOS = ~TOS".

GET_ITER

Implements "TOS = iter(TOS)".

GET_YIELD_FROM_ITER

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

New in version 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.

BINARY_POWER

Implements "TOS = TOS1 ** TOS".

BINARY_MULTIPLY

Implements "TOS = TOS1 * TOS".

BINARY_MATRIX_MULTIPLY

Implements "TOS = TOS1 @ TOS".

New in version 3.5.

BINARY_FLOOR_DIVIDE

Implements "TOS = TOS1 // TOS".

BINARY_TRUE_DIVIDE

Implements "TOS = TOS1 / TOS".

BINARY_MODULO

Implements "TOS = TOS1 % TOS".

BINARY_ADD

Implements "TOS = TOS1 + TOS".

BINARY_SUBTRACT

Implements "TOS = TOS1 - TOS".

BINARY_SUBSCR

Implements "TOS = TOS1[TOS]".

BINARY_LSHIFT

Implements "TOS = TOS1 << TOS".

BINARY_RSHIFT

Implements "TOS = TOS1 >> TOS".

BINARY_AND

Implements "TOS = TOS1 & TOS".

BINARY_XOR

Implements "TOS = TOS1 ^ TOS".

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.

INPLACE_POWER

Implements in-place "TOS = TOS1 ** TOS".

INPLACE_MULTIPLY

Implements in-place "TOS = TOS1 * TOS".

INPLACE_MATRIX_MULTIPLY

Implements in-place "TOS = TOS1 @ TOS".

New in version 3.5.

INPLACE_FLOOR_DIVIDE

Implements in-place "TOS = TOS1 // TOS".

INPLACE_TRUE_DIVIDE

Implements in-place "TOS = TOS1 / TOS".

INPLACE_MODULO

Implements in-place "TOS = TOS1 % TOS".

INPLACE_ADD

Implements in-place "TOS = TOS1 + TOS".

INPLACE_SUBTRACT

Implements in-place "TOS = TOS1 - TOS".

INPLACE_LSHIFT

Implements in-place "TOS = TOS1 << TOS".

INPLACE_RSHIFT

Implements in-place "TOS = TOS1 >> TOS".

INPLACE_AND

Implements in-place "TOS = TOS1 & TOS".

INPLACE_XOR

Implements in-place "TOS = TOS1 ^ TOS".

INPLACE_OR

Implements in-place "TOS = TOS1 | TOS".

STORE_SUBSCR

Implements "TOS1[TOS] = TOS2".

DELETE_SUBSCR

Implements "del TOS1[TOS]".

**Coroutine opcodes**

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__".

New in version 3.5.

GET_AITER

Implements "TOS = get_awaitable(TOS.__aiter__())". See
"GET_AWAITABLE" for details about "get_awaitable"

New in version 3.5.

GET_ANEXT

Implements "PUSH(get_awaitable(TOS.__anext__()))". See
"GET_AWAITABLE" for details about "get_awaitable"

New in version 3.5.

BEFORE_ASYNC_WITH

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

New in version 3.5.

SETUP_ASYNC_WITH

Creates a new frame object.

New in version 3.5.

**Miscellaneous opcodes**

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 "POP_TOP".

BREAK_LOOP

Terminates a loop due to a "break" statement.

CONTINUE_LOOP(target)

Continues a loop due to a "continue" statement. *target* is the
address to jump to (which should be a "FOR_ITER" instruction).

SET_ADD(i)

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

LIST_APPEND(i)

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

MAP_ADD(i)

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

New in version 3.1.

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 TOS to the caller of the function.

YIELD_VALUE

Pops TOS and yields it from a *generator*.

YIELD_FROM

Pops TOS and delegates to it as a subiterator from a *generator*.

New in version 3.3.

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.

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 *".

POP_BLOCK

Removes one block from the block stack. Per frame, there is a
stack of blocks, denoting nested loops, try statements, and such.

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.

END_FINALLY

Terminates a "finally" clause. The interpreter recalls whether the
exception has to be re-raised, or whether the function returns, and
continues with the outer-next block.

LOAD_BUILD_CLASS

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

SETUP_WITH(delta)

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_CLEANUP". Then,
"__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 ("POP_TOP"),
or store it in (a) variable(s) ("STORE_FAST", "STORE_NAME", or
"UNPACK_SEQUENCE").

New in version 3.2.

WITH_CLEANUP_START

Cleans up the stack when a "with" statement block exits. TOS is
the context manager’s "__exit__()" bound method. Below TOS are 1–3
values indicating how/why the finally clause was entered:

* SECOND = "None"

* (SECOND, THIRD) = ("WHY_{RETURN,CONTINUE}"), retval

* SECOND = "WHY_*"; no retval below it

* (SECOND, THIRD, FOURTH) = exc_info()

In the last case, "TOS(SECOND, THIRD, FOURTH)" is called, otherwise
"TOS(None, None, None)". Pushes SECOND and result of the call to
the stack.

WITH_CLEANUP_FINISH

Pops exception type and result of ‘exit’ function call from the
stack.

If the stack represents an exception, *and* the function call
returns a ‘true’ value, this information is “zapped” and replaced
with a single "WHY_SILENCED" to prevent "END_FINALLY" from re-
raising the exception. (But non-local gotos will still be
resumed.)

All of the following opcodes use their arguments.

STORE_NAME(namei)

Implements "name = TOS". *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 TOS into *count* individual values, which are put onto the
stack right-to-left.

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.

STORE_ATTR(namei)

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

DELETE_ATTR(namei)

Implements "del TOS.name", using *namei* as index into "co_names".

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.

BUILD_TUPLE(count)

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

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: "{..., TOS3:
TOS2, TOS1: TOS}".

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. *count*
values are consumed from the stack. The top element on the stack
contains a tuple of keys.

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.

BUILD_TUPLE_UNPACK(count)

Pops *count* iterables from the stack, joins them in a single
tuple, and pushes the result. Implements iterable unpacking in
tuple displays "(*x, *y, *z)".

New in version 3.5.

BUILD_TUPLE_UNPACK_WITH_CALL(count)

This is similar to "BUILD_TUPLE_UNPACK", but is used for "f(*x, *y,
*z)" call syntax. The stack item at position "count + 1" should be
the corresponding callable "f".

New in version 3.6.

BUILD_LIST_UNPACK(count)

This is similar to "BUILD_TUPLE_UNPACK", but pushes a list instead
of tuple. Implements iterable unpacking in list displays "[*x, *y,
*z]".

New in version 3.5.

BUILD_SET_UNPACK(count)

This is similar to "BUILD_TUPLE_UNPACK", but pushes a set instead
of tuple. Implements iterable unpacking in set displays "{*x, *y,
*z}".

New in version 3.5.

BUILD_MAP_UNPACK(count)

Pops *count* mappings from the stack, merges them into a single
dictionary, and pushes the result. Implements dictionary unpacking
in dictionary displays "{**x, **y, **z}".

New in version 3.5.

BUILD_MAP_UNPACK_WITH_CALL(count)

This is similar to "BUILD_MAP_UNPACK", but is used for "f(**x, **y,
**z)" call syntax. The stack item at position "count + 2" should
be the corresponding callable "f".

New in version 3.5.

Changed in version 3.6: The position of the callable is determined
by adding 2 to the opcode argument instead of encoding it in the
second byte of the argument.

LOAD_ATTR(namei)

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

COMPARE_OP(opname)

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

IMPORT_NAME(namei)

Imports the module "co_names[namei]". TOS and TOS1 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 TOS.
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*.

POP_JUMP_IF_TRUE(target)

If TOS is true, sets the bytecode counter to *target*. TOS is
popped.

New in version 3.1.

POP_JUMP_IF_FALSE(target)

If TOS is false, sets the bytecode counter to *target*. TOS is
popped.

New in version 3.1.

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.

New in version 3.1.

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.

New in version 3.1.

JUMP_ABSOLUTE(target)

Set bytecode counter to *target*.

FOR_ITER(delta)

TOS 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 TOS is
popped, and the byte code counter is incremented by *delta*.

LOAD_GLOBAL(namei)

Loads the global named "co_names[namei]" onto the stack.

SETUP_LOOP(delta)

Pushes a block for a loop onto the block stack. The block spans
from the current instruction with a size of *delta* bytes.

SETUP_EXCEPT(delta)

Pushes a try block from a try-except clause onto the block stack.
*delta* points to the first except block.

SETUP_FINALLY(delta)

Pushes a try block from a try-except clause onto the block stack.
*delta* points to the finally block.

LOAD_FAST(var_num)

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

STORE_FAST(var_num)

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

DELETE_FAST(var_num)

Deletes local "co_varnames[var_num]".

STORE_ANNOTATION(namei)

Stores TOS as "locals()['__annotations__'][co_names[namei]] = TOS".

New in version 3.6.

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)]".

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.

LOAD_CLASSDEREF(i)

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

New in version 3.4.

STORE_DEREF(i)

Stores TOS into the cell contained in slot *i* of the cell and free
variable storage.

DELETE_DEREF(i)

Empties the cell contained in slot *i* of the cell and free
variable storage. Used by the "del" statement.

New in version 3.2.

RAISE_VARARGS(argc)

Raises an exception. *argc* indicates the number of parameters to
the raise statement, ranging from 0 to 3. The handler will find
the traceback as TOS2, the parameter as TOS1, and the exception as
TOS.

CALL_FUNCTION(argc)

Calls a function. *argc* indicates the number of positional
arguments. The positional arguments are on the stack, with the
right-most argument on top. Below the arguments, the function
object to call is on the stack. Pops all function arguments, and
the function itself off the stack, and pushes the return value.

Changed in version 3.6: This opcode is used only for calls with
positional arguments.

CALL_FUNCTION_KW(argc)

Calls a function. *argc* indicates the number of arguments
(positional and keyword). The top element on the stack contains a
tuple of keyword argument names. Below the tuple, keyword
arguments are on the stack, in the order corresponding to the
tuple. Below the keyword arguments, the positional arguments are
on the stack, with the right-most parameter on top. Below the
arguments, the function object to call is on the stack. Pops all
function arguments, and the function itself off the stack, and
pushes the return value.

Changed in version 3.6: Keyword arguments are packed in a tuple
instead of a dictionary, *argc* indicates the total number of
arguments

CALL_FUNCTION_EX(flags)

Calls a function. The lowest bit of *flags* indicates whether the
var-keyword argument is placed at the top of the stack. Below the
var-keyword argument, the var-positional argument is on the stack.
Below the arguments, the function object to call is placed. Pops
all function arguments, and the function itself off the stack, and
pushes the return value. Note that this opcode pops at most three
items from the stack. Var-positional and var-keyword arguments are
packed by "BUILD_TUPLE_UNPACK_WITH_CALL" and
"BUILD_MAP_UNPACK_WITH_CALL".

New in version 3.6.

MAKE_FUNCTION(argc)

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 argument objects in positional order

* "0x02" a dictionary of keyword-only parameters’ default values

* "0x04" an annotation dictionary

* "0x08" a tuple containing cells for free variables, making a
closure

* the code associated with the function (at TOS1)

* the *qualified name* of the function (at TOS)

BUILD_SLICE(argc)

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 "slice()" built-in function for more
information.

EXTENDED_ARG(ext)

Prefixes any opcode which has an argument too big to fit into the
default two bytes. *ext* holds two additional bytes which, taken
together with the subsequent opcode’s argument, comprise a four-
byte argument, *ext* being the two most-significant bytes.

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 "str()" on *value* before
formatting it.

* "(flags & 0x03) == 0x02": call "repr()" on *value* before
formatting it.

* "(flags & 0x03) == 0x03": call "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 "PyObject_Format()". The result is
pushed on the stack.

New in version 3.6.

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).

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.

Opcode collections
==================

These collections are provided for automatic introspection of bytecode
instructions:

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.hasconst

Sequence of bytecodes that have a constant parameter.

dis.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).

dis.hasname

Sequence of bytecodes that access an attribute by name.

dis.hasjrel

Sequence of bytecodes that have a relative jump target.

dis.hasjabs

Sequence of bytecodes that have an absolute jump target.

dis.haslocal

Sequence of bytecodes that access a local variable.

dis.hascompare

Sequence of bytecodes of Boolean operations.