32.12. 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)
3 LOAD_FAST 0 (alist)
6 CALL_FUNCTION 1
9 RETURN_VALUE
(The “2” is a line number).
32.12.1. 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 aBytecode
instance yields the bytecode operations asInstruction
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()
.
-
classmethod
Example:
>>> bytecode = dis.Bytecode(myfunc)
>>> for instr in bytecode:
... print(instr.opname)
...
LOAD_GLOBAL
LOAD_FAST
CALL_FUNCTION
RETURN_VALUE
32.12.2. 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:
- the line number, for the first instruction of each line
- the current instruction, indicated as
-->
, - a labelled instruction, indicated with
>>
, - the address of the instruction,
- the operation code name,
- operation parameters, and
- interpretation of the parameters in parentheses.
The parameter interpretation recognizes local and global variable names, constant values, branch targets, and compare operators.
The disassembly is written as text to the supplied file argument if provided and to
sys.stdout
otherwise.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
andco_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.
32.12.3. 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, otherwiseFalse
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, implementsTOS = 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)
, whereget_awaitable(o)
returnso
ifo
is a coroutine object or a generator object with the CO_ITERABLE_COROUTINE flag, or resolveso.__await__
.
-
GET_AITER
Implements
TOS = get_awaitable(TOS.__aiter__())
. SeeGET_AWAITABLE
for details aboutget_awaitable
-
GET_ANEXT
Implements
PUSH(get_awaitable(TOS.__anext__()))
. SeeGET_AWAITABLE
for details aboutget_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
.
-
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 aFOR_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.
-
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.
-
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 implementsfrom 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 byCALL_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 byWITH_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
, orUNPACK_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:- 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, otherwiseTOS(None, None, None)
. Pushes SECOND and result of the call to the stack.- SECOND =
-
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 preventEND_FINALLY
from re-raising the exception. (But non-local gotos will still be resumed.)
All of the following opcodes expect arguments. An argument is two bytes, with the more significant byte last.
-
STORE_NAME
(namei) Implements
name = TOS
. namei is the index of name in the attributeco_names
of the code object. The compiler tries to useSTORE_FAST
orSTORE_GLOBAL
if possible.
-
DELETE_NAME
(namei) Implements
del name
, where namei is the index intoco_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 inco_names
.
-
DELETE_ATTR
(namei) Implements
del TOS.name
, using namei as index intoco_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. The dictionary is pre-sized to hold count entries.
-
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 subsequentSTORE_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 aSTORE_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]
.
-
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 isco_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
argc & 0xFF
default argument objects in positional order(argc >> 8) & 0xFF
pairs of name and default argument, with the name just below the object on the stack, for keyword-only parameters(argc >> 16) & 0x7FFF
parameter annotation objects- a tuple listing the parameter names for the annotations (only if there are ony annotation objects)
- the code associated with the function (at TOS1)
- the qualified name of the function (at TOS)
-
MAKE_CLOSURE
(argc) Creates a new function object, sets its __closure__ slot, and pushes it on the stack. TOS is the qualified name of the function, TOS1 is the code associated with the function, and TOS2 is the tuple containing cells for the closure’s free variables. argc is interpreted as in
MAKE_FUNCTION
; the annotations and defaults are also in the same order below TOS2.
-
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 theslice()
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.
-
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
.
32.12.4. 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.