On 15/05/2015 09:59, Marko Rauhamaa wrote:
The path from decoding a bytecode to the C code that implements it can
be rather convoluted, but there are reasons for each of the
complications -- mainly to do with supporting the ability to override
operators with C and/or Python code.
If you removed those abilities, the implemention would be simpler, and
possibly faster. But then the language wouldn't be Python any more.
I agree that Python's raison-d'être is its dynamism and expressive
power. It definitely shouldn't be sacrificed for performance.
However, in some respects, Python might be going overboard with its
dynamism; are all those dunder methods really needed? Must "false" be
defined so broadly? Must a method lookup necessarily involve object
creation?
What /is/ a method lookup? Is it when you have this:
A.B()
and need to find whether the expression A (or its class or type) has a
name B associated with it? (And it then needs to check whether B is
something that can be called.)
If so, does that have to be done using Python's Dict mechanism? (Ie.
searching for a key 'B' by name and seeing if the object associated with
it is a method. That does not sound efficient.)
(And I guess Python's classes come into play so if B is not part of A's
class then it might be part of some base-class. I can see that it can
get complicated, but I don't use OO so can't speculate further.)
(In the language whose implementation I'm comparing with CPython's, it
doesn't have classes. A.B() can still appear, but .B will need to be an
attribute that the (bytecode) compiler already knows from a prior
definition (usually, some struct or record if A is an expression).
If there is only one .B it knows, then a simple check that A is the
correct type is all that is needed. Otherwise a runtime search through
all .Bs (and a compact table will have been set up for this) is needed
to find the .B that matches A's type. But this is all still pretty quick.
In this context, A.B will need to be some function pointer, and A.B()
will call it.)
--
Bartc
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