[Patches] [ python-Patches-941881 ] PEP309 Partial implementation
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Sun Feb 27 21:43:39 CET 2005
Patches item #941881, was opened at 2004-04-25 19:05
Message generated for change (Comment added) made by pmoore
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Category: Library (Lib)
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Hye-Shik Chang (perky)
Assigned to: Nobody/Anonymous (nobody)
Summary: PEP309 Partial implementation
Initial Comment:
This patch implements functional module which is
introduced by PEP309. It has only 'partial' function as
its member in this stage.
Unittest code is copied and modified slightly from
Patch #931010 by Peter Harris.
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Comment By: Paul Moore (pmoore)
Date: 2005-02-27 20:43
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To build on Windows (at least with mingw gcc, I don't know
about MSVC) you need to assign members of partial_type which
are symbols in the Python DLL at runtime, not compile time.
The following diff probably explains better:
--- functionalmodule.c.orig 2005-02-27
20:41:41.000000000 +000
+++ functionalmodule.c 2005-02-26 21:41:14.000000000 +0000
@@ -197,7 +197,7 @@
0, /* tp_hash */
(ternaryfunc)partial_call, /* tp_call */
0, /* tp_str */
- PyObject_GenericGetAttr, /* tp_getattro */
+ 0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
@@ -220,7 +220,7 @@
0, /* tp_init */
0, /* tp_alloc */
partial_new, /* tp_new */
- PyObject_GC_Del, /* tp_free */
+ 0, /* tp_free */
};
@@ -239,6 +239,8 @@
int i;
PyObject *m;
char *name;
+ partial_type.tp_getattro = PyObject_GenericGetAttr;
+ partial_type.tp_free = PyObject_GC_Del;
PyTypeObject *typelist[] = {
&partial_type,
NULL
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Comment By: Nick Coghlan (ncoghlan)
Date: 2005-02-26 05:27
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Moving the discussion to python-dev :)
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Comment By: Steven Bethard (bediviere)
Date: 2005-02-26 03:58
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Oops -- wrong order of association.
... self.args = args[2:] + func.args
... d = func.kw.copy()
... d.update(kw)
should have been
... self.args = func.args + args[2:]
... kw.update(func.kw)
... self.kw = kw
hopefully these errors didn't confuse my intent too much.
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Comment By: Steven Bethard (bediviere)
Date: 2005-02-26 03:53
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Yes, that's much clearer. I don't remember why I couldn't
get it to work this way before (I tried something quite
similar to this), but I'm glad someone could figure out the
simpler way to do it. ;-)
One potential problem with my proposal -- it doesn't work
for nested partials:
py> class C(object):
... pass
...
py> def func(self, arg1, arg2):
... return self, arg1, arg2
...
py> setattr(C, 'a', partial(func, 'a', 'b'))
py> C().a()
(<__main__.C object at 0x01186470>, 'a', 'b')
py> setattr(C, 'a', partial(partial(func, 'a'), 'b'))
py> C().a()
('a', <__main__.C object at 0x01186370>, 'b')
One possible solution would be to merge nested partials, but
I'm not at all certain this solves all the problems:
py> class partial(object):
... def __init__(*args, **kw):
... self = args[0]
... func = args[1]
... if isinstance(func, partial):
... self.fn = func.fn
... self.args = args[2:] + func.args
... d = func.kw.copy()
... d.update(kw)
... self.kw = d
... else:
... self.fn, self.args, self.kw = (args[1],
args[2:], kw)
... def __call__(self, *args, **kw):
... if kw and self.kw:
... d = self.kw.copy()
... d.update(kw)
... else:
... d = kw or self.kw
... return self.fn(*(self.args + args), **d)
... def __get__(self, obj, type=None):
... if obj is None:
... return self
... return partial(self.fn, obj, *self.args, **self.kw)
...
py> class C(object):
... pass
...
py> def func(self, arg1, arg2):
... return self, arg1, arg2
...
py> setattr(C, 'a', partial(func, 'a', 'b'))
py> C().a()
(<__main__.C object at 0x01186BB0>, 'a', 'b')
py> setattr(C, 'a', partial(partial(func, 'a'), 'b'))
py> C().a()
(<__main__.C object at 0x01186650>, 'b', 'a')
On the other hand, merging nested partials does reduce the
number of function calls, so perhaps it's useful in and of
itself...
----------------------------------------------------------------------
Comment By: Nick Coghlan (ncoghlan)
Date: 2005-02-26 03:45
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If the __get__ method is added to make partial functions
behave like instance methods, the documentation should
probably mention that classmethod() and staticmethod() can
then be used to alter the behaviour:
Py> def f(*args):
... print args
...
Py> class C:
... a = functional.partial(f)
... b = classmethod(functional.partial(f))
... c = staticmethod(functional.partial(f))
...
Py> C().a
<functional.partial object at 0x009E0DD0>
Py> C().a()
(<__main__.C instance at 0x009E6698>,)
Py> C().b()
(<class __main__.C at 0x009DDB40>,)
Py> C().c()
()
(This example used the simpler __get__ implementation I
posted earlier)
----------------------------------------------------------------------
Comment By: Nick Coghlan (ncoghlan)
Date: 2005-02-26 03:27
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Steve's suggestion does sound good, but can't it simply be
implemented with the PEP implementation and the following
__get__ method?:
def __get__(self, obj, type=None):
if obj is None:
return self
return partial(self.func, obj, *self.args, **self.kwargs)
----------------------------------------------------------------------
Comment By: Nick Coghlan (ncoghlan)
Date: 2005-02-26 03:17
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Peter Harris already wrote docs in Patch 931007. Presumably
they are still accurate, or perky would have said something.
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Comment By: Martin v. Löwis (loewis)
Date: 2005-02-25 20:34
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In this form, the patch cannot be applied, since it lacks
documentation changes. It might be that perky does not
consider himself fluent enough in English to write the
documentation - any other volunteers?
I also think there is value to bediviere's point, even
though the PEP currently specifies partial() differently.
----------------------------------------------------------------------
Comment By: Steven Bethard (bediviere)
Date: 2005-02-19 20:38
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It might be nice if partial objects were usable as
instancemethods, like functions are. Note the following
behavior with the current patch:
>>> import functional
>>> class C(object):
... pass
...
>>> def func(self, arg):
... return arg
...
>>> for item in ['a', 'b', 'c']:
... setattr(C, item, functional.partial(func, item))
...
>>> C().a()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: func() takes exactly 2 arguments (1 given)
If functional.partial was instead defined like:
class partial(object):
def __init__(*args, **kwargs):
self = args[0]
try:
self.func = args[1]
except IndexError:
raise TypeError('expected 2 or more arguments,
got ' %
len(args))
self.obj = ()
self.args = args[2:]
self.kwargs = kwargs
def __call__(self, *args, **kwargs):
if kwargs and self.kwargs:
d = self.kwargs.copy()
d.update(kwargs)
else:
d = kwargs or self.kwargs
return self.func(*(self.obj + self.args + args), **d)
def __get__(self, obj, type=None):
if obj is None:
return self
result = partial(self.func, *self.args, **self.kwargs)
result.obj = (obj,)
return result
where an appropriate __get__ method is provided, then
partial objects behave properly when set as attributes to a
class:
py> def test():
... class C(object):
... pass
... def func(self, arg):
... return arg
... for item in ['a', 'b', 'c']:
... setattr(C, item, functional.partial(func, item))
... c = C()
... return c.a(), c.b(), c.c()
...
py> test()
('a', 'b', 'c')
----------------------------------------------------------------------
Comment By: Nick Coghlan (ncoghlan)
Date: 2004-08-11 01:11
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I have tested this patch on Windows, and it passes its own
test suite, without affecting any other tests.
However, PCBuild\pythoncore.vcproj & PC\config.c require
modification to allow Python to pick up the new module
correctly.
Patch #1006948 created with the needed changes (also removes
unneeded ODBC references from pythoncore.vcproj as I am
using the free MS toolkits to build here)
My patch definitely needs to be checked by someone with a
copy of Vis Studio 2003!
----------------------------------------------------------------------
Comment By: Paul Moore (pmoore)
Date: 2004-08-03 21:23
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OK, a real need beats my theoretical worries :-) Consider me
convinced.
----------------------------------------------------------------------
Comment By: Bob Ippolito (etrepum)
Date: 2004-05-18 05:05
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I would use partial in situations where speed can matter (imap,
commonly used event handlers, etc.), so a fast C implementation would
be nice to have.
----------------------------------------------------------------------
Comment By: Paul Moore (pmoore)
Date: 2004-04-27 09:03
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Yes, that looks like a significant speed improvement :-) I was
basing my assumptions on the comments made in the PEP.
Sorry.
But I still wonder if having the implementation in Python
wouldn't be better from a maintenance point of view. (As well
as all the arguments about usefulness as sample code, ability
to backport, etc etc, that have come up on python-dev
regarding moving other Python library modules into C...).
----------------------------------------------------------------------
Comment By: Hye-Shik Chang (perky)
Date: 2004-04-27 03:05
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Python-version (function) ... 1.19 2.69
Python-version (class) ... 2.61 2.38
C-version ... 0.50 0.37
(former value is for 100000 instanciations and latter is for
100000 calls.)
And, C version have a facility that changing attributes after
the instantiation that is supported by class version only.
----------------------------------------------------------------------
Comment By: Paul Moore (pmoore)
Date: 2004-04-26 20:30
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Why implement this in C? I can't imagine that the
performance improvement will be that significant. A pure
Python module in the standard library seems to me to be a
far better idea. As the PEP says, "the case for a built-in
coded in C is not very strong". And a Python module is good
self-documentation.
I prefer the function version suggested in the PEP (credited
to Carl Banks) over the class-based one. You need to take a
little care to avoid capturing argument names:
def partial(*args, **kwds):
def callit(*moreargs, **morekwds):
kw = kwds.copy()
kw.update(morekwds)
return args[0](*(args[1:]+moreargs), **kw)
return callit
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