17.10.1 Python Byte Code Instructions
Keywords: lib

##
17.10.1 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.

`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`.

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`.

`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`.

`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[:TOS1]`.

`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]`.

`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.

`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.

`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_LOOP` delta
  Iterate over a sequence. TOS is the current index, TOS1 the sequence. First, the next element is computed. If the sequence is exhausted, increment byte code counter by delta. Otherwise, push the sequence, the incremented counter, and the current item onto the stack.

`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]`.

`SET_LINENO` lineno
  Sets the current line number to lineno.

`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.

`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.