gagsl-py2 at yahoo.com.ar
Mon Mar 19 01:54:08 CET 2007
En Sun, 18 Mar 2007 10:21:27 -0300, Dustan <DustanGroups at gmail.com>
> 21 0 LOAD_DEREF 0 (func)
> 3 LOAD_DEREF 1 (internalData)
> 6 LOAD_FAST 0 (args)
> 9 CALL_FUNCTION_VAR 1
> 12 RETURN_VALUE
> What's the difference between 'LOAD_DEREF', 'LOAD_FAST', and
> 'LOAD_CONST', and, as seen at http://docs.python.org/lib/module-dis.html,
> 'LOAD_GLOBAL'? I can imagine that 'LOAD_GLOBAL' loads a global, but
> seeing as python is such a dynamic language, how exactly is it
> supposed to distinguish between them?
The Python interpreter executes a stack-based machine. Look at
Python/compile.c for the code generation and Python/ceval.c for the code
LOAD_CONST pushes a constant onto the stack (all constants are previously
built and stored as attribute co_consts of the code object). LOAD_FAST and
LOAD_GLOBAL pushes a local or global variable reference. (The compiler
knows whether a name is local or not, just by lexical analysis).
LOAD_DEREF appears to be used for accessing variables inside closures, I'm
> I don't understand the following at all: 'DUP_TOP', 'ROT_TWO'. Any
They manipulate the stack. DUP_TOP duplicates the top entry; ROT_TWO swaps
the two top entries.
> What does 'INPLACE_ADD' mean, if not in place addition, and if it is
> in place addition, why does it need to 'STORE_ATTR' afterward?
That corresponds to A += B. The compiler can't know if A has or not an
__iadd__ method; even if A implements __iadd__, that method could return a
different object, not always A (it *may* try to do the operation inplace,
but that might not always be possible). When the inplace method is not
implemented, __add__ is used (so effectively A += B is computed as A = A+B)
More information about the Python-list