> i am a longtime Reader of this list and this is the first time i a dare to
> speak up.
> Apology in advance for any noise, silly comments and not posting to
> python-ideas ;).
Welcome!
> Well how about implementing guards like in pypy?
Guards would allow to generate specialized functions without a JIT.
Dummy example:
def func(arg):
arg *= 1
arg += 0
return arg * 16
Can be optimized to:
def func(arg):
if type(arg) is int:
# fast path
return arg << 4
else:
# slow path
arg *= 1
arg += 0
return arg * 16
I prefer a check before executing the code, rather than an exception
and reexecute the same code twice.
Specializing all functions would waste a lot of memory, so it should
only be applied on some very specific cases... It can also be slower
if the guard check is slower than the function body! But I bet that
guards would help to enable more aggressive optimizations, or at least
make some optimizations safe.
Dave Malcolm wrote a patch modifying eval.c to support specialized
functions. See the
http://bugs.python.org/issue10399
I don't know yet what is the best approach for CPython.
--
For the specific case of builtin functions and types, I made two
changes in Python 3.3:
* the type of the builtins mapping can now be any mapping (Python <=
3.2 requires the dict type, dict subtypes are disallowed)
* "new" types.MappingProxyType type to create a read-only proxy for a
mapping (see also the rejected PEP 416)
We may combine these two changes to use a read-only mapping for
builtins. It would at least help to ensure that an application does
not monkeypatch builtin functions/types.
Victor
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