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.
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).
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.
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.
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
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:
-->
,>>
,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.
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.
The get_instructions()
function and Bytecode
class provide
details of bytecode instructions as Instruction
instances:
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.
DUP_TOP_TWO
¶Duplicates the two references on top of the stack, leaving them in the same order.
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__
.
GET_AITER
¶Implements TOS = get_awaitable(TOS.__aiter__())
. See GET_AWAITABLE
for details about get_awaitable
GET_ANEXT
¶Implements PUSH(get_awaitable(TOS.__anext__()))
. See GET_AWAITABLE
for details about get_awaitable
BEFORE_ASYNC_WITH
¶Resolves __aenter__
and __aexit__
from the object on top of the
stack. Pushes __aexit__
and result of __aenter__()
to the stack.
SETUP_ASYNC_WITH
¶Creates a new frame object.
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
.
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.
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.
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
).
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:
None
WHY_{RETURN,CONTINUE}
), retvalWHY_*
; no retval below itIn 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_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
(oparg)¶This is similar to BUILD_MAP_UNPACK
,
but is used for f(**x, **y, **z)
call syntax. The lowest byte of
oparg is the count of mappings, the relative position of the
corresponding callable f
is encoded in the second byte of oparg.
New in version 3.5.
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.
POP_JUMP_IF_FALSE
(target)¶If TOS is false, sets the bytecode counter to target. TOS is popped.
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.
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.
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.
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.
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. The low byte of argc indicates the number of positional parameters, the high byte the number of keyword parameters. On the stack, the opcode finds the keyword parameters first. For each keyword argument, the value is on top of the key. Below the keyword parameters, the positional parameters are on the stack, with the right-most parameter on top. Below the parameters, 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.
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 order0x02
a dictionary of keyword-only parameters’ default values0x04
an annotation dictionary0x08
a tuple containing cells for free variables, making a closureBUILD_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.
CALL_FUNCTION_VAR
(argc)¶Calls a function. argc is interpreted as in CALL_FUNCTION
. The
top element on the stack contains the variable argument list, followed by
keyword and positional arguments.
CALL_FUNCTION_KW
(argc)¶Calls a function. argc is interpreted as in CALL_FUNCTION
. The
top element on the stack contains the keyword arguments dictionary, followed
by explicit keyword and positional arguments.
CALL_FUNCTION_VAR_KW
(argc)¶Calls a function. argc is interpreted as in CALL_FUNCTION
. The
top element on the stack contains the keyword arguments dictionary, followed
by the variable-arguments tuple, followed by explicit keyword and positional
arguments.
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 take arguments < HAVE_ARGUMENT
and those which do
>= HAVE_ARGUMENT
.
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.