:mod:`dis` --- Disassembler for Python bytecode =============================================== .. module:: dis :synopsis: Disassembler for Python bytecode. **Source code:** :source:`Lib/dis.py` -------------- The :mod:`dis` module supports the analysis of CPython :term:`bytecode` by disassembling it. The CPython bytecode which this module takes as an input is defined in the file :file:`Include/opcode.h` and used by the compiler and the interpreter. .. impl-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 :func:`myfunc`:: def myfunc(alist): return len(alist) the following command can be used to display the disassembly of :func:`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). Bytecode analysis ----------------- .. versionadded:: 3.4 The bytecode analysis API allows pieces of Python code to be wrapped in a :class:`Bytecode` object that provides easy access to details of the compiled code. .. class:: Bytecode(x, *, first_line=None, current_offset=None) Analyse the bytecode corresponding to a function, method, string of source code, or a code object (as returned by :func:`compile`). This is a convenience wrapper around many of the functions listed below, most notably :func:`get_instructions`, as iterating over a :class:`Bytecode` instance yields the bytecode operations as :class:`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 :meth:`.dis` will display a "current instruction" marker against the specified opcode. .. classmethod:: from_traceback(tb) Construct a :class:`Bytecode` instance from the given traceback, setting *current_offset* to the instruction responsible for the exception. .. data:: codeobj The compiled code object. .. data:: first_line The first source line of the code object (if available) .. method:: dis() Return a formatted view of the bytecode operations (the same as printed by :func:`dis.dis`, but returned as a multi-line string). .. method:: info() Return a formatted multi-line string with detailed information about the code object, like :func:`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 :mod:`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: .. function:: code_info(x) Return a formatted multi-line string with detailed code object information for the supplied function, 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. .. versionadded:: 3.2 .. function:: 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. .. versionadded:: 3.2 .. versionchanged:: 3.4 Added *file* parameter. .. function:: dis(x=None, *, file=None) Disassemble the *x* object. *x* can denote either a module, a class, a method, a function, 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. 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 :func:`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. .. versionchanged:: 3.4 Added *file* parameter. .. function:: 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. .. versionchanged:: 3.4 Added *file* parameter. .. function:: disassemble(code, lasti=-1, *, file=None) 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. .. versionchanged:: 3.4 Added *file* parameter. .. function:: 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 :class:`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. .. versionadded:: 3.4 .. function:: 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. .. function:: findlabels(code) Detect all offsets in the code object *code* which are jump targets, and return a list of these offsets. .. function:: stack_effect(opcode, [oparg]) Compute the stack effect of *opcode* with argument *oparg*. .. versionadded:: 3.4 .. _bytecodes: Python Bytecode Instructions ---------------------------- The :func:`get_instructions` function and :class:`Bytecode` class provide details of bytecode instructions as :class:`Instruction` instances: .. class:: Instruction Details for a bytecode operation .. data:: opcode numeric code for operation, corresponding to the opcode values listed below and the bytecode values in the :ref:`opcode_collections`. .. data:: opname human readable name for operation .. data:: arg numeric argument to operation (if any), otherwise None .. data:: argval resolved arg value (if known), otherwise same as arg .. data:: argrepr human readable description of operation argument .. data:: offset start index of operation within bytecode sequence .. data:: starts_line line started by this opcode (if any), otherwise None .. data:: is_jump_target ``True`` if other code jumps to here, otherwise ``False`` .. versionadded:: 3.4 The Python compiler currently generates the following bytecode instructions. **General instructions** .. opcode:: NOP Do nothing code. Used as a placeholder by the bytecode optimizer. .. opcode:: POP_TOP Removes the top-of-stack (TOS) item. .. opcode:: ROT_TWO Swaps the two top-most stack items. .. opcode:: ROT_THREE Lifts second and third stack item one position up, moves top down to position three. .. opcode:: DUP_TOP Duplicates the reference on top of the stack. .. opcode:: 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. .. opcode:: UNARY_POSITIVE Implements ``TOS = +TOS``. .. opcode:: UNARY_NEGATIVE Implements ``TOS = -TOS``. .. opcode:: UNARY_NOT Implements ``TOS = not TOS``. .. opcode:: UNARY_INVERT Implements ``TOS = ~TOS``. .. opcode:: GET_ITER Implements ``TOS = iter(TOS)``. **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. .. opcode:: BINARY_POWER Implements ``TOS = TOS1 ** TOS``. .. opcode:: BINARY_MULTIPLY Implements ``TOS = TOS1 * TOS``. .. opcode:: BINARY_FLOOR_DIVIDE Implements ``TOS = TOS1 // TOS``. .. opcode:: BINARY_TRUE_DIVIDE Implements ``TOS = TOS1 / TOS``. .. opcode:: BINARY_MODULO Implements ``TOS = TOS1 % TOS``. .. opcode:: BINARY_ADD Implements ``TOS = TOS1 + TOS``. .. opcode:: BINARY_SUBTRACT Implements ``TOS = TOS1 - TOS``. .. opcode:: BINARY_SUBSCR Implements ``TOS = TOS1[TOS]``. .. opcode:: BINARY_LSHIFT Implements ``TOS = TOS1 << TOS``. .. opcode:: BINARY_RSHIFT Implements ``TOS = TOS1 >> TOS``. .. opcode:: BINARY_AND Implements ``TOS = TOS1 & TOS``. .. opcode:: BINARY_XOR Implements ``TOS = TOS1 ^ TOS``. .. opcode:: 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. .. opcode:: INPLACE_POWER Implements in-place ``TOS = TOS1 ** TOS``. .. opcode:: INPLACE_MULTIPLY Implements in-place ``TOS = TOS1 * TOS``. .. opcode:: INPLACE_FLOOR_DIVIDE Implements in-place ``TOS = TOS1 // TOS``. .. opcode:: INPLACE_TRUE_DIVIDE Implements in-place ``TOS = TOS1 / TOS``. .. opcode:: INPLACE_MODULO Implements in-place ``TOS = TOS1 % TOS``. .. opcode:: INPLACE_ADD Implements in-place ``TOS = TOS1 + TOS``. .. opcode:: INPLACE_SUBTRACT Implements in-place ``TOS = TOS1 - TOS``. .. opcode:: INPLACE_LSHIFT Implements in-place ``TOS = TOS1 << TOS``. .. opcode:: INPLACE_RSHIFT Implements in-place ``TOS = TOS1 >> TOS``. .. opcode:: INPLACE_AND Implements in-place ``TOS = TOS1 & TOS``. .. opcode:: INPLACE_XOR Implements in-place ``TOS = TOS1 ^ TOS``. .. opcode:: INPLACE_OR Implements in-place ``TOS = TOS1 | TOS``. .. opcode:: STORE_SUBSCR Implements ``TOS1[TOS] = TOS2``. .. opcode:: DELETE_SUBSCR Implements ``del TOS1[TOS]``. **Miscellaneous opcodes** .. opcode:: 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 :opcode:`POP_TOP`. .. opcode:: BREAK_LOOP Terminates a loop due to a :keyword:`break` statement. .. opcode:: CONTINUE_LOOP (target) Continues a loop due to a :keyword:`continue` statement. *target* is the address to jump to (which should be a :opcode:`FOR_ITER` instruction). .. opcode:: SET_ADD (i) Calls ``set.add(TOS1[-i], TOS)``. Used to implement set comprehensions. .. opcode:: LIST_APPEND (i) Calls ``list.append(TOS[-i], TOS)``. Used to implement list comprehensions. .. opcode:: MAP_ADD (i) Calls ``dict.setitem(TOS1[-i], TOS, TOS1)``. Used to implement dict comprehensions. For all of the :opcode:`SET_ADD`, :opcode:`LIST_APPEND` and :opcode:`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. .. opcode:: RETURN_VALUE Returns with TOS to the caller of the function. .. opcode:: YIELD_VALUE Pops TOS and yields it from a :term:`generator`. .. opcode:: YIELD_FROM Pops TOS and delegates to it as a subiterator from a :term:`generator`. .. versionadded:: 3.3 .. opcode:: 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 *``. .. opcode:: POP_BLOCK Removes one block from the block stack. Per frame, there is a stack of blocks, denoting nested loops, try statements, and such. .. opcode:: 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. .. opcode:: END_FINALLY Terminates a :keyword:`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. .. opcode:: LOAD_BUILD_CLASS Pushes :func:`builtins.__build_class__` onto the stack. It is later called by :opcode:`CALL_FUNCTION` to construct a class. .. opcode:: SETUP_WITH (delta) This opcode performs several operations before a with block starts. First, it loads :meth:`~object.__exit__` from the context manager and pushes it onto the stack for later use by :opcode:`WITH_CLEANUP`. Then, :meth:`~object.__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 (:opcode:`POP_TOP`), or store it in (a) variable(s) (:opcode:`STORE_FAST`, :opcode:`STORE_NAME`, or :opcode:`UNPACK_SEQUENCE`). .. opcode:: WITH_CLEANUP Cleans up the stack when a :keyword:`with` statement block exits. TOS is the context manager's :meth:`__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)``. In addition, TOS is removed 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 :opcode:`END_FINALLY` from re-raising the exception. (But non-local gotos will still be resumed.) .. XXX explain the WHY stuff! All of the following opcodes expect arguments. An argument is two bytes, with the more significant byte last. .. opcode:: STORE_NAME (namei) Implements ``name = TOS``. *namei* is the index of *name* in the attribute :attr:`co_names` of the code object. The compiler tries to use :opcode:`STORE_FAST` or :opcode:`STORE_GLOBAL` if possible. .. opcode:: DELETE_NAME (namei) Implements ``del name``, where *namei* is the index into :attr:`co_names` attribute of the code object. .. opcode:: UNPACK_SEQUENCE (count) Unpacks TOS into *count* individual values, which are put onto the stack right-to-left. .. opcode:: 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 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. .. opcode:: STORE_ATTR (namei) Implements ``TOS.name = TOS1``, where *namei* is the index of name in :attr:`co_names`. .. opcode:: DELETE_ATTR (namei) Implements ``del TOS.name``, using *namei* as index into :attr:`co_names`. .. opcode:: STORE_GLOBAL (namei) Works as :opcode:`STORE_NAME`, but stores the name as a global. .. opcode:: DELETE_GLOBAL (namei) Works as :opcode:`DELETE_NAME`, but deletes a global name. .. opcode:: LOAD_CONST (consti) Pushes ``co_consts[consti]`` onto the stack. .. opcode:: LOAD_NAME (namei) Pushes the value associated with ``co_names[namei]`` onto the stack. .. opcode:: BUILD_TUPLE (count) Creates a tuple consuming *count* items from the stack, and pushes the resulting tuple onto the stack. .. opcode:: BUILD_LIST (count) Works as :opcode:`BUILD_TUPLE`, but creates a list. .. opcode:: BUILD_SET (count) Works as :opcode:`BUILD_TUPLE`, but creates a set. .. opcode:: BUILD_MAP (count) Pushes a new dictionary object onto the stack. The dictionary is pre-sized to hold *count* entries. .. opcode:: LOAD_ATTR (namei) Replaces TOS with ``getattr(TOS, co_names[namei])``. .. opcode:: COMPARE_OP (opname) Performs a Boolean operation. The operation name can be found in ``cmp_op[opname]``. .. opcode:: IMPORT_NAME (namei) Imports the module ``co_names[namei]``. TOS and TOS1 are popped and provide the *fromlist* and *level* arguments of :func:`__import__`. The module object is pushed onto the stack. The current namespace is not affected: for a proper import statement, a subsequent :opcode:`STORE_FAST` instruction modifies the namespace. .. opcode:: 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 :opcode:`STORE_FAST` instruction. .. opcode:: JUMP_FORWARD (delta) Increments bytecode counter by *delta*. .. opcode:: POP_JUMP_IF_TRUE (target) If TOS is true, sets the bytecode counter to *target*. TOS is popped. .. opcode:: POP_JUMP_IF_FALSE (target) If TOS is false, sets the bytecode counter to *target*. TOS is popped. .. opcode:: 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. .. opcode:: 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. .. opcode:: JUMP_ABSOLUTE (target) Set bytecode counter to *target*. .. opcode:: FOR_ITER (delta) TOS is an :term:`iterator`. Call its :meth:`~iterator.__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*. .. opcode:: LOAD_GLOBAL (namei) Loads the global named ``co_names[namei]`` onto the stack. .. opcode:: 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. .. opcode:: SETUP_EXCEPT (delta) Pushes a try block from a try-except clause onto the block stack. *delta* points to the first except block. .. opcode:: SETUP_FINALLY (delta) Pushes a try block from a try-except clause onto the block stack. *delta* points to the finally block. .. opcode:: STORE_MAP Store a key and value pair in a dictionary. Pops the key and value while leaving the dictionary on the stack. .. opcode:: LOAD_FAST (var_num) Pushes a reference to the local ``co_varnames[var_num]`` onto the stack. .. opcode:: STORE_FAST (var_num) Stores TOS into the local ``co_varnames[var_num]``. .. opcode:: DELETE_FAST (var_num) Deletes local ``co_varnames[var_num]``. .. opcode:: 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)]``. .. opcode:: 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. .. opcode:: LOAD_CLASSDEREF (i) Much like :opcode:`LOAD_DEREF` but first checks the locals dictionary before consulting the cell. This is used for loading free variables in class bodies. .. opcode:: STORE_DEREF (i) Stores TOS into the cell contained in slot *i* of the cell and free variable storage. .. opcode:: DELETE_DEREF (i) Empties the cell contained in slot *i* of the cell and free variable storage. Used by the :keyword:`del` statement. .. opcode:: 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. .. opcode:: 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. .. opcode:: 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 :term:`qualified name` of the function (at TOS) .. opcode:: MAKE_CLOSURE (argc) Creates a new function object, sets its *__closure__* slot, and pushes it on the stack. TOS is the :term:`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. The function also has *argc* default parameters, which are found below the cells. .. opcode:: BUILD_SLICE (argc) .. index:: builtin: slice 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 :func:`slice` built-in function for more information. .. opcode:: 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. .. opcode:: CALL_FUNCTION_VAR (argc) Calls a function. *argc* is interpreted as in :opcode:`CALL_FUNCTION`. The top element on the stack contains the variable argument list, followed by keyword and positional arguments. .. opcode:: CALL_FUNCTION_KW (argc) Calls a function. *argc* is interpreted as in :opcode:`CALL_FUNCTION`. The top element on the stack contains the keyword arguments dictionary, followed by explicit keyword and positional arguments. .. opcode:: CALL_FUNCTION_VAR_KW (argc) Calls a function. *argc* is interpreted as in :opcode:`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. .. opcode:: 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``. .. _opcode_collections: Opcode collections ------------------ These collections are provided for automatic introspection of bytecode instructions: .. data:: opname Sequence of operation names, indexable using the bytecode. .. data:: opmap Dictionary mapping operation names to bytecodes. .. data:: cmp_op Sequence of all compare operation names. .. data:: hasconst Sequence of bytecodes that have a constant parameter. .. data:: 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). .. data:: hasname Sequence of bytecodes that access an attribute by name. .. data:: hasjrel Sequence of bytecodes that have a relative jump target. .. data:: hasjabs Sequence of bytecodes that have an absolute jump target. .. data:: haslocal Sequence of bytecodes that access a local variable. .. data:: hascompare Sequence of bytecodes of Boolean operations.