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30.10.1 Python Byte Code Instructions


30.10.1 Python Byte Code Instructions

The Python compiler currently generates the following byte code instructions.

STOP_CODE
Indicates end-of-code to the compiler, not used by the interpreter.

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.

ROT_FOUR
Lifts second, third and forth stack item one position up, moves top down to position four.

DUP_TOP
Duplicates the reference on top of the stack.

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_CONVERT
Implements TOS = `TOS`.

UNARY_INVERT
Implements TOS = ~TOS.

GET_ITER
Implements TOS = iter(TOS).

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_DIVIDE
Implements TOS = TOS1 / TOS when from __future__ import division is not in effect.

BINARY_FLOOR_DIVIDE
Implements TOS = TOS1 // TOS.

BINARY_TRUE_DIVIDE
Implements TOS = TOS1 / TOS when from __future__ import division is in effect.

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 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_DIVIDE
Implements in-place TOS = TOS1 / TOS when from __future__ import division is not in effect.

INPLACE_FLOOR_DIVIDE
Implements in-place TOS = TOS1 // TOS.

INPLACE_TRUE_DIVIDE
Implements in-place TOS = TOS1 / TOS when from __future__ import division is in effect.

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.

The slice opcodes take up to three parameters.

SLICE+0
Implements TOS = TOS[:].

SLICE+1
Implements TOS = TOS1[TOS:].

SLICE+2
Implements TOS = TOS1[:TOS].

SLICE+3
Implements TOS = TOS2[TOS1:TOS].

Slice assignment needs even an additional parameter. As any statement, they put nothing on the stack.

STORE_SLICE+0
Implements TOS[:] = TOS1.

STORE_SLICE+1
Implements TOS1[TOS:] = TOS2.

STORE_SLICE+2
Implements TOS1[:TOS] = TOS2.

STORE_SLICE+3
Implements TOS2[TOS1:TOS] = TOS3.

DELETE_SLICE+0
Implements del TOS[:].

DELETE_SLICE+1
Implements del TOS1[TOS:].

DELETE_SLICE+2
Implements del TOS1[:TOS].

DELETE_SLICE+3
Implements del TOS2[TOS1:TOS].

STORE_SUBSCR
Implements TOS1[TOS] = TOS2.

DELETE_SUBSCR
Implements del TOS1[TOS].

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_STACK.

PRINT_ITEM
Prints TOS to the file-like object bound to sys.stdout. There is one such instruction for each item in the print statement.

PRINT_ITEM_TO
Like PRINT_ITEM, but prints the item second from TOS to the file-like object at TOS. This is used by the extended print statement.

PRINT_NEWLINE
Prints a new line on sys.stdout. This is generated as the last operation of a print statement, unless the statement ends with a comma.

PRINT_NEWLINE_TO
Like PRINT_NEWLINE, but prints the new line on the file-like object on the TOS. This is used by the extended print statement.

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 a FOR_ITER instruction).

LIST_APPEND
Calls list.append(TOS1, TOS). Used to implement list comprehensions.

LOAD_LOCALS
Pushes a reference to the locals of the current scope on the stack. This is used in the code for a class definition: After the class body is evaluated, the locals are passed to the class definition.

RETURN_VALUE
Returns with TOS to the caller of the function.

YIELD_VALUE
Pops TOS and yields it from a generator.

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 *.

EXEC_STMT
Implements exec TOS2,TOS1,TOS. The compiler fills missing optional parameters with None.

POP_BLOCK
Removes one block from the block stack. Per frame, there is a stack of blocks, denoting nested loops, try statements, and such.

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.

BUILD_CLASS
Creates a new class object. TOS is the methods dictionary, TOS1 the tuple of the names of the base classes, and TOS2 the class name.

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 attribute co_names of the code object. The compiler tries to use STORE_LOCAL 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.

DUP_TOPX    count
Duplicate count items, keeping them in the same order. Due to implementation limits, count should be between 1 and 5 inclusive.

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_MAP    zero
Pushes a new empty dictionary object onto the stack. The argument is ignored and set to zero by the compiler.

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]. 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 byte code counter by delta.

JUMP_IF_TRUE    delta
If TOS is true, increment the byte code counter by delta. TOS is left on the stack.

JUMP_IF_FALSE    delta
If TOS is false, increment the byte code counter by delta. TOS is not changed.

JUMP_ABSOLUTE    target
Set byte code 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 is co_freevars[i - len(co_cellvars)].

LOAD_DEREF    i
Loads the cell contained in slot i of the cell and free variable storage. Pushes a reference to the object the cell contains on the stack.

STORE_DEREF    i
Stores TOS into the cell contained in slot i of the cell and free variable storage.

SET_LINENO    lineno
This opcode is obsolete.

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.

MAKE_FUNCTION    argc
Pushes a new function object on the stack. TOS is the code associated with the function. The function object is defined to have argc default parameters, which are found below TOS.

MAKE_CLOSURE    argc
Creates a new function object, sets its func_closure slot, and pushes it on the stack. TOS is the code associated with the function. If the code object has N free variables, the next N items on the stack are the cells for these variables. The function also has argc default parameters, where are found before the cells.

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 the slice() built-in function for more information.

EXTENDED_ARG    ext
Prefixes any opcode which has an argument too big to fit into the default two bytes. ext holds two additional bytes which, taken together with the subsequent opcode's argument, comprise a four-byte argument, ext being the two most-significant bytes.

CALL_FUNCTION_VAR    argc
Calls a function. argc is interpreted as in CALL_FUNCTION. The top element on the stack contains the variable argument list, followed by keyword and positional arguments.

CALL_FUNCTION_KW    argc
Calls a function. argc is interpreted as in CALL_FUNCTION. The top element on the stack contains the keyword arguments dictionary, followed by explicit keyword and positional arguments.

CALL_FUNCTION_VAR_KW    argc
Calls a function. argc is interpreted as in CALL_FUNCTION. The top element on the stack contains the keyword arguments dictionary, followed by the variable-arguments tuple, followed by explicit keyword and positional arguments.

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.
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