2 :mod:`dis` --- Disassembler for Python bytecode
3 ===============================================
6 :synopsis: Disassembler for Python bytecode.
9 The :mod:`dis` module supports the analysis of Python :term:`bytecode` by disassembling
10 it. Since there is no Python assembler, this module defines the Python assembly
11 language. The Python bytecode which this module takes as an input is defined
12 in the file :file:`Include/opcode.h` and used by the compiler and the
15 Example: Given the function :func:`myfunc`::
20 the following command can be used to get the disassembly of :func:`myfunc`::
23 2 0 LOAD_GLOBAL 0 (len)
28 (The "2" is a line number).
30 The :mod:`dis` module defines the following functions and constants:
33 .. function:: dis([bytesource])
35 Disassemble the *bytesource* object. *bytesource* can denote either a module, a
36 class, a method, a function, or a code object. For a module, it disassembles
37 all functions. For a class, it disassembles all methods. For a single code
38 sequence, it prints one line per bytecode instruction. If no object is
39 provided, it disassembles the last traceback.
42 .. function:: distb([tb])
44 Disassembles the top-of-stack function of a traceback, using the last traceback
45 if none was passed. The instruction causing the exception is indicated.
48 .. function:: disassemble(code[, lasti])
50 Disassembles a code object, indicating the last instruction if *lasti* was
51 provided. The output is divided in the following columns:
53 #. the line number, for the first instruction of each line
54 #. the current instruction, indicated as ``-->``,
55 #. a labelled instruction, indicated with ``>>``,
56 #. the address of the instruction,
57 #. the operation code name,
58 #. operation parameters, and
59 #. interpretation of the parameters in parentheses.
61 The parameter interpretation recognizes local and global variable names,
62 constant values, branch targets, and compare operators.
65 .. function:: disco(code[, lasti])
67 A synonym for disassemble. It is more convenient to type, and kept for
68 compatibility with earlier Python releases.
73 Sequence of operation names, indexable using the bytecode.
78 Dictionary mapping bytecodes to operation names.
83 Sequence of all compare operation names.
88 Sequence of bytecodes that have a constant parameter.
93 Sequence of bytecodes that access a free variable.
98 Sequence of bytecodes that access an attribute by name.
103 Sequence of bytecodes that have a relative jump target.
108 Sequence of bytecodes that have an absolute jump target.
113 Sequence of bytecodes that access a local variable.
118 Sequence of bytecodes of Boolean operations.
123 Python Bytecode Instructions
124 ----------------------------
126 The Python compiler currently generates the following bytecode instructions.
129 .. opcode:: STOP_CODE ()
131 Indicates end-of-code to the compiler, not used by the interpreter.
136 Do nothing code. Used as a placeholder by the bytecode optimizer.
139 .. opcode:: POP_TOP ()
141 Removes the top-of-stack (TOS) item.
144 .. opcode:: ROT_TWO ()
146 Swaps the two top-most stack items.
149 .. opcode:: ROT_THREE ()
151 Lifts second and third stack item one position up, moves top down to position
155 .. opcode:: ROT_FOUR ()
157 Lifts second, third and forth stack item one position up, moves top down to
161 .. opcode:: DUP_TOP ()
163 Duplicates the reference on top of the stack.
165 Unary Operations take the top of the stack, apply the operation, and push the
166 result back on the stack.
169 .. opcode:: UNARY_POSITIVE ()
171 Implements ``TOS = +TOS``.
174 .. opcode:: UNARY_NEGATIVE ()
176 Implements ``TOS = -TOS``.
179 .. opcode:: UNARY_NOT ()
181 Implements ``TOS = not TOS``.
184 .. opcode:: UNARY_CONVERT ()
186 Implements ``TOS = `TOS```.
189 .. opcode:: UNARY_INVERT ()
191 Implements ``TOS = ~TOS``.
194 .. opcode:: GET_ITER ()
196 Implements ``TOS = iter(TOS)``.
198 Binary operations remove the top of the stack (TOS) and the second top-most
199 stack item (TOS1) from the stack. They perform the operation, and put the
200 result back on the stack.
203 .. opcode:: BINARY_POWER ()
205 Implements ``TOS = TOS1 ** TOS``.
208 .. opcode:: BINARY_MULTIPLY ()
210 Implements ``TOS = TOS1 * TOS``.
213 .. opcode:: BINARY_DIVIDE ()
215 Implements ``TOS = TOS1 / TOS`` when ``from __future__ import division`` is not
219 .. opcode:: BINARY_FLOOR_DIVIDE ()
221 Implements ``TOS = TOS1 // TOS``.
224 .. opcode:: BINARY_TRUE_DIVIDE ()
226 Implements ``TOS = TOS1 / TOS`` when ``from __future__ import division`` is in
230 .. opcode:: BINARY_MODULO ()
232 Implements ``TOS = TOS1 % TOS``.
235 .. opcode:: BINARY_ADD ()
237 Implements ``TOS = TOS1 + TOS``.
240 .. opcode:: BINARY_SUBTRACT ()
242 Implements ``TOS = TOS1 - TOS``.
245 .. opcode:: BINARY_SUBSCR ()
247 Implements ``TOS = TOS1[TOS]``.
250 .. opcode:: BINARY_LSHIFT ()
252 Implements ``TOS = TOS1 << TOS``.
255 .. opcode:: BINARY_RSHIFT ()
257 Implements ``TOS = TOS1 >> TOS``.
260 .. opcode:: BINARY_AND ()
262 Implements ``TOS = TOS1 & TOS``.
265 .. opcode:: BINARY_XOR ()
267 Implements ``TOS = TOS1 ^ TOS``.
270 .. opcode:: BINARY_OR ()
272 Implements ``TOS = TOS1 | TOS``.
274 In-place operations are like binary operations, in that they remove TOS and
275 TOS1, and push the result back on the stack, but the operation is done in-place
276 when TOS1 supports it, and the resulting TOS may be (but does not have to be)
280 .. opcode:: INPLACE_POWER ()
282 Implements in-place ``TOS = TOS1 ** TOS``.
285 .. opcode:: INPLACE_MULTIPLY ()
287 Implements in-place ``TOS = TOS1 * TOS``.
290 .. opcode:: INPLACE_DIVIDE ()
292 Implements in-place ``TOS = TOS1 / TOS`` when ``from __future__ import
293 division`` is not in effect.
296 .. opcode:: INPLACE_FLOOR_DIVIDE ()
298 Implements in-place ``TOS = TOS1 // TOS``.
301 .. opcode:: INPLACE_TRUE_DIVIDE ()
303 Implements in-place ``TOS = TOS1 / TOS`` when ``from __future__ import
304 division`` is in effect.
307 .. opcode:: INPLACE_MODULO ()
309 Implements in-place ``TOS = TOS1 % TOS``.
312 .. opcode:: INPLACE_ADD ()
314 Implements in-place ``TOS = TOS1 + TOS``.
317 .. opcode:: INPLACE_SUBTRACT ()
319 Implements in-place ``TOS = TOS1 - TOS``.
322 .. opcode:: INPLACE_LSHIFT ()
324 Implements in-place ``TOS = TOS1 << TOS``.
327 .. opcode:: INPLACE_RSHIFT ()
329 Implements in-place ``TOS = TOS1 >> TOS``.
332 .. opcode:: INPLACE_AND ()
334 Implements in-place ``TOS = TOS1 & TOS``.
337 .. opcode:: INPLACE_XOR ()
339 Implements in-place ``TOS = TOS1 ^ TOS``.
342 .. opcode:: INPLACE_OR ()
344 Implements in-place ``TOS = TOS1 | TOS``.
346 The slice opcodes take up to three parameters.
349 .. opcode:: SLICE+0 ()
351 Implements ``TOS = TOS[:]``.
354 .. opcode:: SLICE+1 ()
356 Implements ``TOS = TOS1[TOS:]``.
359 .. opcode:: SLICE+2 ()
361 Implements ``TOS = TOS1[:TOS]``.
364 .. opcode:: SLICE+3 ()
366 Implements ``TOS = TOS2[TOS1:TOS]``.
368 Slice assignment needs even an additional parameter. As any statement, they put
369 nothing on the stack.
372 .. opcode:: STORE_SLICE+0 ()
374 Implements ``TOS[:] = TOS1``.
377 .. opcode:: STORE_SLICE+1 ()
379 Implements ``TOS1[TOS:] = TOS2``.
382 .. opcode:: STORE_SLICE+2 ()
384 Implements ``TOS1[:TOS] = TOS2``.
387 .. opcode:: STORE_SLICE+3 ()
389 Implements ``TOS2[TOS1:TOS] = TOS3``.
392 .. opcode:: DELETE_SLICE+0 ()
394 Implements ``del TOS[:]``.
397 .. opcode:: DELETE_SLICE+1 ()
399 Implements ``del TOS1[TOS:]``.
402 .. opcode:: DELETE_SLICE+2 ()
404 Implements ``del TOS1[:TOS]``.
407 .. opcode:: DELETE_SLICE+3 ()
409 Implements ``del TOS2[TOS1:TOS]``.
412 .. opcode:: STORE_SUBSCR ()
414 Implements ``TOS1[TOS] = TOS2``.
417 .. opcode:: DELETE_SUBSCR ()
419 Implements ``del TOS1[TOS]``.
421 Miscellaneous opcodes.
424 .. opcode:: PRINT_EXPR ()
426 Implements the expression statement for the interactive mode. TOS is removed
427 from the stack and printed. In non-interactive mode, an expression statement is
428 terminated with ``POP_STACK``.
431 .. opcode:: PRINT_ITEM ()
433 Prints TOS to the file-like object bound to ``sys.stdout``. There is one such
434 instruction for each item in the :keyword:`print` statement.
437 .. opcode:: PRINT_ITEM_TO ()
439 Like ``PRINT_ITEM``, but prints the item second from TOS to the file-like object
440 at TOS. This is used by the extended print statement.
443 .. opcode:: PRINT_NEWLINE ()
445 Prints a new line on ``sys.stdout``. This is generated as the last operation of
446 a :keyword:`print` statement, unless the statement ends with a comma.
449 .. opcode:: PRINT_NEWLINE_TO ()
451 Like ``PRINT_NEWLINE``, but prints the new line on the file-like object on the
452 TOS. This is used by the extended print statement.
455 .. opcode:: BREAK_LOOP ()
457 Terminates a loop due to a :keyword:`break` statement.
460 .. opcode:: CONTINUE_LOOP (target)
462 Continues a loop due to a :keyword:`continue` statement. *target* is the
463 address to jump to (which should be a ``FOR_ITER`` instruction).
466 .. opcode:: LIST_APPEND ()
468 Calls ``list.append(TOS1, TOS)``. Used to implement list comprehensions.
471 .. opcode:: LOAD_LOCALS ()
473 Pushes a reference to the locals of the current scope on the stack. This is used
474 in the code for a class definition: After the class body is evaluated, the
475 locals are passed to the class definition.
478 .. opcode:: RETURN_VALUE ()
480 Returns with TOS to the caller of the function.
483 .. opcode:: YIELD_VALUE ()
485 Pops ``TOS`` and yields it from a :term:`generator`.
488 .. opcode:: IMPORT_STAR ()
490 Loads all symbols not starting with ``'_'`` directly from the module TOS to the
491 local namespace. The module is popped after loading all names. This opcode
492 implements ``from module import *``.
495 .. opcode:: EXEC_STMT ()
497 Implements ``exec TOS2,TOS1,TOS``. The compiler fills missing optional
498 parameters with ``None``.
501 .. opcode:: POP_BLOCK ()
503 Removes one block from the block stack. Per frame, there is a stack of blocks,
504 denoting nested loops, try statements, and such.
507 .. opcode:: END_FINALLY ()
509 Terminates a :keyword:`finally` clause. The interpreter recalls whether the
510 exception has to be re-raised, or whether the function returns, and continues
511 with the outer-next block.
514 .. opcode:: BUILD_CLASS ()
516 Creates a new class object. TOS is the methods dictionary, TOS1 the tuple of
517 the names of the base classes, and TOS2 the class name.
520 .. opcode:: WITH_CLEANUP ()
522 Cleans up the stack when a :keyword:`with` statement block exits. TOS is the
523 context manager's :meth:`__exit__` bound method. Below that are 1--3 values
524 indicating how/why the finally clause was entered:
527 * (SECOND, THIRD) = (``WHY_{RETURN,CONTINUE}``), retval
528 * SECOND = ``WHY_*``; no retval below it
529 * (SECOND, THIRD, FOURTH) = exc_info()
531 In the last case, ``TOS(SECOND, THIRD, FOURTH)`` is called, otherwise
532 ``TOS(None, None, None)``.
534 In addition, if the stack represents an exception, *and* the function call
535 returns a 'true' value, this information is "zapped", to prevent ``END_FINALLY``
536 from re-raising the exception. (But non-local gotos should still be resumed.)
538 .. XXX explain the WHY stuff!
541 All of the following opcodes expect arguments. An argument is two bytes, with
542 the more significant byte last.
544 .. opcode:: STORE_NAME (namei)
546 Implements ``name = TOS``. *namei* is the index of *name* in the attribute
547 :attr:`co_names` of the code object. The compiler tries to use ``STORE_LOCAL``
548 or ``STORE_GLOBAL`` if possible.
551 .. opcode:: DELETE_NAME (namei)
553 Implements ``del name``, where *namei* is the index into :attr:`co_names`
554 attribute of the code object.
557 .. opcode:: UNPACK_SEQUENCE (count)
559 Unpacks TOS into *count* individual values, which are put onto the stack
563 .. opcode:: DUP_TOPX (count)
565 Duplicate *count* items, keeping them in the same order. Due to implementation
566 limits, *count* should be between 1 and 5 inclusive.
569 .. opcode:: STORE_ATTR (namei)
571 Implements ``TOS.name = TOS1``, where *namei* is the index of name in
575 .. opcode:: DELETE_ATTR (namei)
577 Implements ``del TOS.name``, using *namei* as index into :attr:`co_names`.
580 .. opcode:: STORE_GLOBAL (namei)
582 Works as ``STORE_NAME``, but stores the name as a global.
585 .. opcode:: DELETE_GLOBAL (namei)
587 Works as ``DELETE_NAME``, but deletes a global name.
590 .. opcode:: LOAD_CONST (consti)
592 Pushes ``co_consts[consti]`` onto the stack.
595 .. opcode:: LOAD_NAME (namei)
597 Pushes the value associated with ``co_names[namei]`` onto the stack.
600 .. opcode:: BUILD_TUPLE (count)
602 Creates a tuple consuming *count* items from the stack, and pushes the resulting
603 tuple onto the stack.
606 .. opcode:: BUILD_LIST (count)
608 Works as ``BUILD_TUPLE``, but creates a list.
611 .. opcode:: BUILD_MAP (count)
613 Pushes a new dictionary object onto the stack. The dictionary is pre-sized
614 to hold *count* entries.
617 .. opcode:: LOAD_ATTR (namei)
619 Replaces TOS with ``getattr(TOS, co_names[namei])``.
622 .. opcode:: COMPARE_OP (opname)
624 Performs a Boolean operation. The operation name can be found in
628 .. opcode:: IMPORT_NAME (namei)
630 Imports the module ``co_names[namei]``. The module object is pushed onto the
631 stack. The current namespace is not affected: for a proper import statement, a
632 subsequent ``STORE_FAST`` instruction modifies the namespace.
635 .. opcode:: IMPORT_FROM (namei)
637 Loads the attribute ``co_names[namei]`` from the module found in TOS. The
638 resulting object is pushed onto the stack, to be subsequently stored by a
639 ``STORE_FAST`` instruction.
642 .. opcode:: JUMP_FORWARD (delta)
644 Increments bytecode counter by *delta*.
647 .. opcode:: JUMP_IF_TRUE (delta)
649 If TOS is true, increment the bytecode counter by *delta*. TOS is left on the
653 .. opcode:: JUMP_IF_FALSE (delta)
655 If TOS is false, increment the bytecode counter by *delta*. TOS is not
659 .. opcode:: JUMP_ABSOLUTE (target)
661 Set bytecode counter to *target*.
664 .. opcode:: FOR_ITER (delta)
666 ``TOS`` is an :term:`iterator`. Call its :meth:`next` method. If this
667 yields a new value, push it on the stack (leaving the iterator below it). If
668 the iterator indicates it is exhausted ``TOS`` is popped, and the bytecode
669 counter is incremented by *delta*.
672 .. opcode:: LOAD_GLOBAL (namei)
674 Loads the global named ``co_names[namei]`` onto the stack.
677 .. opcode:: SETUP_LOOP (delta)
679 Pushes a block for a loop onto the block stack. The block spans from the
680 current instruction with a size of *delta* bytes.
683 .. opcode:: SETUP_EXCEPT (delta)
685 Pushes a try block from a try-except clause onto the block stack. *delta* points
686 to the first except block.
689 .. opcode:: SETUP_FINALLY (delta)
691 Pushes a try block from a try-except clause onto the block stack. *delta* points
692 to the finally block.
694 .. opcode:: STORE_MAP ()
696 Store a key and value pair in a dictionary. Pops the key and value while leaving
697 the dictionary on the stack.
699 .. opcode:: LOAD_FAST (var_num)
701 Pushes a reference to the local ``co_varnames[var_num]`` onto the stack.
704 .. opcode:: STORE_FAST (var_num)
706 Stores TOS into the local ``co_varnames[var_num]``.
709 .. opcode:: DELETE_FAST (var_num)
711 Deletes local ``co_varnames[var_num]``.
714 .. opcode:: LOAD_CLOSURE (i)
716 Pushes a reference to the cell contained in slot *i* of the cell and free
717 variable storage. The name of the variable is ``co_cellvars[i]`` if *i* is
718 less than the length of *co_cellvars*. Otherwise it is ``co_freevars[i -
722 .. opcode:: LOAD_DEREF (i)
724 Loads the cell contained in slot *i* of the cell and free variable storage.
725 Pushes a reference to the object the cell contains on the stack.
728 .. opcode:: STORE_DEREF (i)
730 Stores TOS into the cell contained in slot *i* of the cell and free variable
734 .. opcode:: SET_LINENO (lineno)
736 This opcode is obsolete.
739 .. opcode:: RAISE_VARARGS (argc)
741 Raises an exception. *argc* indicates the number of parameters to the raise
742 statement, ranging from 0 to 3. The handler will find the traceback as TOS2,
743 the parameter as TOS1, and the exception as TOS.
746 .. opcode:: CALL_FUNCTION (argc)
748 Calls a function. The low byte of *argc* indicates the number of positional
749 parameters, the high byte the number of keyword parameters. On the stack, the
750 opcode finds the keyword parameters first. For each keyword argument, the value
751 is on top of the key. Below the keyword parameters, the positional parameters
752 are on the stack, with the right-most parameter on top. Below the parameters,
753 the function object to call is on the stack.
756 .. opcode:: MAKE_FUNCTION (argc)
758 Pushes a new function object on the stack. TOS is the code associated with the
759 function. The function object is defined to have *argc* default parameters,
760 which are found below TOS.
763 .. opcode:: MAKE_CLOSURE (argc)
765 Creates a new function object, sets its *func_closure* slot, and pushes it on
766 the stack. TOS is the code associated with the function, TOS1 the tuple
767 containing cells for the closure's free variables. The function also has
768 *argc* default parameters, which are found below the cells.
771 .. opcode:: BUILD_SLICE (argc)
773 .. index:: builtin: slice
775 Pushes a slice object on the stack. *argc* must be 2 or 3. If it is 2,
776 ``slice(TOS1, TOS)`` is pushed; if it is 3, ``slice(TOS2, TOS1, TOS)`` is
777 pushed. See the :func:`slice` built-in function for more information.
780 .. opcode:: EXTENDED_ARG (ext)
782 Prefixes any opcode which has an argument too big to fit into the default two
783 bytes. *ext* holds two additional bytes which, taken together with the
784 subsequent opcode's argument, comprise a four-byte argument, *ext* being the two
785 most-significant bytes.
788 .. opcode:: CALL_FUNCTION_VAR (argc)
790 Calls a function. *argc* is interpreted as in ``CALL_FUNCTION``. The top element
791 on the stack contains the variable argument list, followed by keyword and
792 positional arguments.
795 .. opcode:: CALL_FUNCTION_KW (argc)
797 Calls a function. *argc* is interpreted as in ``CALL_FUNCTION``. The top element
798 on the stack contains the keyword arguments dictionary, followed by explicit
799 keyword and positional arguments.
802 .. opcode:: CALL_FUNCTION_VAR_KW (argc)
804 Calls a function. *argc* is interpreted as in ``CALL_FUNCTION``. The top
805 element on the stack contains the keyword arguments dictionary, followed by the
806 variable-arguments tuple, followed by explicit keyword and positional arguments.
809 .. opcode:: HAVE_ARGUMENT ()
811 This is not really an opcode. It identifies the dividing line between opcodes
812 which don't take arguments ``< HAVE_ARGUMENT`` and those which do ``>=