dis — Disassembler for Python bytecode - Python 3.12.0a3 documentation 编辑

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.

Changed in version 3.10: The argument of jump, exception handling and loop instructions is now the instruction offset rather than the byte offset.

Changed in version 3.11: Some instructions are accompanied by one or more inline cache entries, which take the form of CACHE instructions. These instructions are hidden by default, but can be shown by passing show_caches=True to any dis utility. Furthermore, the interpreter now adapts the bytecode to specialize it for different runtime conditions. The adaptive bytecode can be shown by passing adaptive=True.

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 RESUME                   0

  3           2 LOAD_GLOBAL              1 (NULL + len)
             14 LOAD_FAST                0 (alist)
             16 CALL                     1
             26 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, show_caches=False, adaptive=False)

Analyse the bytecode corresponding to a function, generator, asynchronous generator, coroutine, 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.

If show_caches is True, dis() will display inline cache entries used by the interpreter to specialize the bytecode.

If adaptive is True, dis() will display specialized bytecode that may be different from the original bytecode.

classmethod from_traceback(tb, *, show_caches=False): 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().

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

Changed in version 3.11: Added the show_caches and adaptive parameters.

Example:

>>> bytecode = dis.Bytecode(myfunc)
>>> for instr in bytecode:
...     print(instr.opname)
...
RESUME
LOAD_GLOBAL
LOAD_FAST
CALL
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, asynchronous generator, coroutine, 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.

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

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, depth=None, show_caches=False, adaptive=False)

Disassemble the x object. x can denote either a module, a class, a method, a function, a generator, an asynchronous generator, a coroutine, 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. It also recursively disassembles nested code objects (the code of comprehensions, generator expressions and nested functions, and the code used for building nested classes). 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.

The maximal depth of recursion is limited by depth unless it is None. depth=0 means no recursion.

If show_caches is True, this function will display inline cache entries used by the interpreter to specialize the bytecode.

If adaptive is True, this function will display specialized bytecode that may be different from the original bytecode.

Changed in version 3.4: Added file parameter.

Changed in version 3.7: Implemented recursive disassembling and added depth parameter.

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.distb(tb=None, *, file=None, show_caches=False, adaptive=False)

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.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.disassemble(code, lasti=- 1, *, file=None, show_caches=False, adaptive=False)

dis.disco(code, lasti=- 1, *, file=None, show_caches=False, adaptive=False)

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.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.get_instructions(x, *, first_line=None, show_caches=False, adaptive=False)

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.

The show_caches and adaptive parameters work as they do in dis().

New in version 3.4.

Changed in version 3.11: Added the show_caches and adaptive parameters.

dis.findlinestarts(code)

This generator function uses the co_lines method 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.

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

Changed in version 3.10: The PEP 626 co_lines method is used instead of the co_firstlineno and co_lnotab attributes of the code object.

dis.findlabels(code): Detect all offsets in the raw compiled bytecode string code which are jump targets, and return a list of these offsets.

dis.stack_effect(opcode, oparg=None, *, jump=None)

Compute the stack effect of opcode with argument oparg.

If the code has a jump target and jump is True, stack_effect() will return the stack effect of jumping. If jump is False, it will return the stack effect of not jumping. And if jump is None (default), it will return the maximal stack effect of both cases.

New in version 3.4.

Changed in version 3.8: Added jump parameter.

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 any), otherwise None

argrepr: human readable description of operation argument (if any), otherwise an empty string.

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

positions: dis.Positions object holding the start and end locations that are covered by this instruction.

New in version 3.4.

Changed in version 3.11: Field positions is added.

class dis.Positions

In case the information is not available, some fields might be None.

lineno

end_lineno

col_offset

end_col_offset

New in version 3.11.

The Python compiler currently generates the following bytecode instructions.

General instructions

NOP: Do nothing code. Used as a placeholder by the bytecode optimizer, and to generate line tracing events.

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

END_FOR

Removes the top two values from the stack. Equivalent to POP_TOP; POP_TOP. Used to clean up at the end of loops, hence the name.

New in version 3.12.

COPY(i)

Push the i-th item to the top of the stack. The item is not removed from its original location.

New in version 3.11.

SWAP(i)

Swap TOS with the item at position i.

New in version 3.11.

CACHE

Rather than being an actual instruction, this opcode is used to mark extra space for the interpreter to cache useful data directly in the bytecode itself. It is automatically hidden by all dis utilities, but can be viewed with show_caches=True.

Logically, this space is part of the preceding instruction. Many opcodes expect to be followed by an exact number of caches, and will instruct the interpreter to skip over them at runtime.

Populated caches can look like arbitrary instructions, so great care should be taken when reading or modifying raw, adaptive bytecode containing quickened data.

New in version 3.11.

Unary operations

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

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 and in-place operations

In the following, TOS is the top-of-stack. TOS1, TOS2, TOS3 are the second, third and fourth items on the stack, respectively.

Binary operations remove the top two items from the stack (TOS and TOS1). They perform the operation, then put the result back on the stack.

In-place operations are like binary operations, 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.

BINARY_OP(op)

Implements the binary and in-place operators (depending on the value of op). TOS = TOS1 op TOS.

New in version 3.11.

BINARY_SUBSCR: Implements TOS = TOS1[TOS].

STORE_SUBSCR: Implements TOS1[TOS] = TOS2.

DELETE_SUBSCR: Implements del TOS1[TOS].

BINARY_SLICE

Implements TOS = TOS2[TOS1:TOS].

New in version 3.12.

STORE_SLICE

Implements TOS2[TOS1:TOS] = TOS3.

New in version 3.12.

Coroutine opcodes

GET_AWAITABLE(where)

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__.

If the where operand is nonzero, it indicates where the instruction occurs:
1 After a call to __aenter__
2 After a call to __aexit__

New in version 3.5.

Changed in version 3.11: Previously, this instruction did not have an oparg.

GET_AITER

Implements TOS = TOS.__aiter__().

New in version 3.5.

Changed in version 3.7: Returning awaitable objects from __aiter__ is no longer supported.

GET_ANEXT

Pushes get_awaitable(TOS.__anext__()) to the stack. See GET_AWAITABLE for details about get_awaitable.

New in version 3.5.

END_ASYNC_FOR

Terminates an async for loop. Handles an exception raised when awaiting a next item. If TOS is StopAsyncIteration pop 3 values from the stack and restore the exception state using the second of them. Otherwise re-raise the exception using the value from the stack. An exception handler block is removed from the block stack.

New in version 3.8:

Changed in version 3.11: Exception representation on the stack now consist of one, not three, items.

CLEANUP_THROW

Handles an exception raised during a throw() or close() call through the current frame. If TOS is an instance of StopIteration, pop three values from the stack and push its value member. Otherwise, re-raise TOS.

New in version 3.12.

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.

Miscellaneous opcodes

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

LIST_APPEND(i): Calls list.append(TOS1[-i], TOS). Used to implement list comprehensions.

MAP_ADD(i)

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

New in version 3.1.

Changed in version 3.8: Map value is TOS and map key is TOS1. Before, those were reversed.

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.
Changed in version 3.11: oparg set to be the stack depth, for efficient handling on frames.

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.

POP_EXCEPT: Pops a value from the stack, which is used to restore the exception state.
Changed in version 3.11: Exception representation on the stack now consist of one, not three, items.

RERAISE

Re-raises the exception currently on top of the stack. If oparg is non-zero, pops an additional value from the stack which is used to set f_lasti of the current frame.

New in version 3.9.

Changed in version 3.11: Exception representation on the stack now consist of one, not three, items.

PUSH_EXC_INFO

Pops a value from the stack. Pushes the current exception to the top of the stack. Pushes the value originally popped back to the stack. Used in exception handlers.

New in version 3.11.

CHECK_EXC_MATCH

Performs exception matching for except. Tests whether the TOS1 is an exception matching TOS. Pops TOS and pushes the boolean result of the test.

New in version 3.11.

CHECK_EG_MATCH

Performs exception matching for except*. Applies split(TOS) on the exception group representing TOS1.

In case of a match, pops two items from the stack and pushes the non-matching subgroup (None in case of full match) followed by the matching subgroup. When there is no match, pops one item (the match type) and pushes None.

New in version 3.11.

PREP_RERAISE_STAR

Combines the raised and reraised exceptions list from TOS, into an exception group to propagate from a try-except* block. Uses the original exception group from TOS1 to reconstruct the structure of reraised exceptions. Pops two items from the stack and pushes the exception to reraise or None if there isn’t one.

New in version 3.11.

WITH_EXCEPT_START

Calls the function in position 4 on the stack with arguments (type, val, tb) representing the exception at the top of the stack. Used to implement the call context_manager.__exit__(*exc_info()) when an exception has occurred in a with statement.

New in version 3.9.

Changed in version 3.11: The __exit__ function is in position 4 of the stack rather than 7. Exception representation on the stack now consist of one, not three, items.

LOAD_ASSERTION_ERROR

Pushes AssertionError onto the stack. Used by the assert statement.

New in version 3.9.

LOAD_BUILD_CLASS: Pushes builtins.__build_class__() onto the stack. It is later called to construct a class.

BEFORE_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_EXCEPT_START. Then, __enter__() is called. Finally, the result of calling the __enter__() method is pushed onto the stack.

New in version 3.11.

GET_LEN

Push len(TOS) onto the stack.

New in version 3.10.

MATCH_MAPPING

If TOS is an instance of collections.abc.Mapping (or, more technically: if it has the Py_TPFLAGS_MAPPING flag set in its tp_flags), push True onto the stack. Otherwise, push False.

New in version 3.10.

MATCH_SEQUENCE

If TOS is an instance of collections.abc.Sequence and is not an instance of str/bytes/bytearray (or, more technically: if it has the Py_TPFLAGS_SEQUENCE flag set in its tp_flags), push True onto the stack. Otherwise, push False.

New in version 3.10.

MATCH_KEYS

TOS is a tuple of mapping keys, and TOS1 is the match subject. If TOS1 contains all of the keys in TOS, push a tuple containing the corresponding values. Otherwise, push None.

New in version 3.10.

Changed in version 3.11: Previously, this instruction also pushed a boolean value indicating success (True) or failure (False).

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. Pops the top element on the stack which contains a tuple of keys, then starting from TOS1, pops count values to form values in the built dictionary.

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.

LIST_EXTEND(i)

Calls list.extend(TOS1[-i], TOS). Used to build lists.

New in version 3.9.

SET_UPDATE(i)

Calls set.update(TOS1[-i], TOS). Used to build sets.

New in version 3.9.

DICT_UPDATE(i)

Calls dict.update(TOS1[-i], TOS). Used to build dicts.

New in version 3.9.

DICT_MERGE(i)

Like DICT_UPDATE but raises an exception for duplicate keys.

New in version 3.9.

LOAD_ATTR(namei)

If the low bit of namei is not set, this replaces TOS with getattr(TOS, co_names[namei>>1]).

If the low bit of namei is set, this will attempt to load a method named co_names[namei>>1] from the TOS object. TOS is popped. This bytecode distinguishes two cases: if TOS has a method with the correct name, the bytecode pushes the unbound method and TOS. TOS will be used as the first argument (self) by CALL when calling the unbound method. Otherwise, NULL and the object return by the attribute lookup are pushed.

Changed in version 3.12: If the low bit of namei is set, then a NULL or self is pushed to the stack before the attribute or unbound method respectively.

COMPARE_OP(opname): Performs a Boolean operation. The operation name can be found in cmp_op[opname].

IS_OP(invert)

Performs is comparison, or is not if invert is 1.

New in version 3.9.

CONTAINS_OP(invert)

Performs in comparison, or not in if invert is 1.

New in version 3.9.

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.

JUMP_BACKWARD(delta)

Decrements bytecode counter by delta. Checks for interrupts.

New in version 3.11.

JUMP_BACKWARD_NO_INTERRUPT(delta)

Decrements bytecode counter by delta. Does not check for interrupts.

New in version 3.11.

POP_JUMP_IF_TRUE(delta)

If TOS is true, increments the bytecode counter by delta. TOS is popped.

Changed in version 3.11: The oparg is now a relative delta rather than an absolute target. This opcode is a pseudo-instruction, replaced in final bytecode by the directed versions (forward/backward).

Changed in version 3.12: This is no longer a pseudo-instruction.

POP_JUMP_IF_FALSE(delta)

If TOS is false, increments the bytecode counter by delta. TOS is popped.

Changed in version 3.11: The oparg is now a relative delta rather than an absolute target. This opcode is a pseudo-instruction, replaced in final bytecode by the directed versions (forward/backward).

Changed in version 3.12: This is no longer a pseudo-instruction.

POP_JUMP_IF_NOT_NONE(delta)

If TOS is not None, increments the bytecode counter by delta. TOS is popped.

New in version 3.11.

Changed in version 3.12: This is no longer a pseudo-instruction.

POP_JUMP_IF_NONE(delta)

If TOS is None, increments the bytecode counter by delta. TOS is popped.

New in version 3.11.

Changed in version 3.12: This is no longer a pseudo-instruction.

JUMP_IF_TRUE_OR_POP(delta)

If TOS is true, increments the bytecode counter by delta and leaves TOS on the stack. Otherwise (TOS is false), TOS is popped.

New in version 3.1.

Changed in version 3.11: The oparg is now a relative delta rather than an absolute target.

JUMP_IF_FALSE_OR_POP(delta)

If TOS is false, increments the bytecode counter by delta and leaves TOS on the stack. Otherwise (TOS is true), TOS is popped.

New in version 3.1.

Changed in version 3.11: The oparg is now a relative delta rather than an absolute 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 then the byte code counter is incremented by delta.

Changed in version 3.12: Up until 3.11 the iterator was popped when it was exhausted.

LOAD_GLOBAL(namei)

Loads the global named co_names[namei>>1] onto the stack.

Changed in version 3.11: If the low bit of namei is set, then a NULL is pushed to the stack before the global variable.

LOAD_FAST(var_num)

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

Changed in version 3.12: This opcode is now only used in situations where the local variable is guaranteed to be initialized. It cannot raise UnboundLocalError.

LOAD_FAST_CHECK(var_num)

Pushes a reference to the local co_varnames[var_num] onto the stack, raising an UnboundLocalError if the local variable has not been initialized.

New in version 3.12.

STORE_FAST(var_num): Stores TOS into the local co_varnames[var_num].

DELETE_FAST(var_num): Deletes local co_varnames[var_num].

MAKE_CELL(i)

Creates a new cell in slot i. If that slot is empty then that value is stored into the new cell.

New in version 3.11.

LOAD_CLOSURE(i)

Pushes a reference to the cell contained in slot i of the “fast locals” storage. The name of the variable is co_fastlocalnames[i].

Note that LOAD_CLOSURE is effectively an alias for LOAD_FAST. It exists to keep bytecode a little more readable.