From f4cb48a72b20b2d166d5303426ab4098243c35e1 Mon Sep 17 00:00:00 2001 From: Nick Coghlan Date: Sun, 3 Nov 2013 16:41:46 +1000 Subject: Issue #4331: Added functools.partialmethod Initial patch by Alon Horev --- Doc/library/functools.rst | 43 ++++++++++++++++- Doc/whatsnew/3.4.rst | 20 +++++++- Lib/functools.py | 78 +++++++++++++++++++++++++++++- Lib/test/test_functools.py | 116 +++++++++++++++++++++++++++++++++++++++++++++ Misc/NEWS | 2 + 5 files changed, 255 insertions(+), 4 deletions(-) diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst index 14e1351..4eb263a 100644 --- a/Doc/library/functools.rst +++ b/Doc/library/functools.rst @@ -194,6 +194,48 @@ The :mod:`functools` module defines the following functions: 18 +.. class:: partialmethod(func, *args, **keywords) + + Return a new :class:`partialmethod` descriptor which behaves + like :class:`partial` except that it is designed to be used as a method + definition rather than being directly callable. + + *func* must be a :term:`descriptor` or a callable (objects which are both, + like normal functions, are handled as descriptors). + + When *func* is a descriptor (such as a normal Python function, + :func:`classmethod`, :func:`staticmethod`, :func:`abstractmethod` or + another instance of :class:`partialmethod`), calls to ``__get__`` are + delegated to the underlying descriptor, and an appropriate + :class:`partial` object returned as the result. + + When *func* is a non-descriptor callable, an appropriate bound method is + created dynamically. This behaves like a normal Python function when + used as a method: the *self* argument will be inserted as the first + positional argument, even before the *args* and *keywords* supplied to + the :class:`partialmethod` constructor. + + Example:: + + >>> class Cell(object): + ... @property + ... def alive(self): + ... return self._alive + ... def set_state(self, state): + ... self._alive = bool(state) + ... set_alive = partialmethod(set_alive, True) + ... set_dead = partialmethod(set_alive, False) + ... + >>> c = Cell() + >>> c.alive + False + >>> c.set_alive() + >>> c.alive + True + + .. versionadded:: 3.4 + + .. function:: reduce(function, iterable[, initializer]) Apply *function* of two arguments cumulatively to the items of *sequence*, from @@ -431,4 +473,3 @@ differences. For instance, the :attr:`__name__` and :attr:`__doc__` attributes are not created automatically. Also, :class:`partial` objects defined in classes behave like static methods and do not transform into bound methods during instance attribute look-up. - diff --git a/Doc/whatsnew/3.4.rst b/Doc/whatsnew/3.4.rst index a570af8..ed6daee 100644 --- a/Doc/whatsnew/3.4.rst +++ b/Doc/whatsnew/3.4.rst @@ -342,7 +342,25 @@ handling). functools --------- -New :func:`functools.singledispatch` decorator: see the :pep:`443`. +The new :func:`~functools.partialmethod` descriptor bring partial argument +application to descriptors, just as :func:`~functools.partial` provides +for normal callables. The new descriptor also makes it easier to get +arbitrary callables (including :func:`~functools.partial` instances) +to behave like normal instance methods when included in a class definition. + +(Contributed by Alon Horev and Nick Coghlan in :issue:`4331`) + +The new :func:`~functools.singledispatch` decorator brings support for +single-dispatch generic functions to the Python standard library. Where +object oriented programming focuses on grouping multiple operations on a +common set of data into a class, a generic function focuses on grouping +multiple implementations of an operation that allows it to work with +*different* kinds of data. + +.. seealso:: + + :pep:`443` - Single-dispatch generic functions + PEP written and implemented by Łukasz Langa. hashlib diff --git a/Lib/functools.py b/Lib/functools.py index 6a6974f..8989361 100644 --- a/Lib/functools.py +++ b/Lib/functools.py @@ -19,7 +19,7 @@ except ImportError: pass from abc import get_cache_token from collections import namedtuple -from types import MappingProxyType +from types import MappingProxyType, MethodType from weakref import WeakKeyDictionary try: from _thread import RLock @@ -223,8 +223,9 @@ except ImportError: ### partial() argument application ################################################################################ +# Purely functional, no descriptor behaviour def partial(func, *args, **keywords): - """new function with partial application of the given arguments + """New function with partial application of the given arguments and keywords. """ def newfunc(*fargs, **fkeywords): @@ -241,6 +242,79 @@ try: except ImportError: pass +# Descriptor version +class partialmethod(object): + """Method descriptor with partial application of the given arguments + and keywords. + + Supports wrapping existing descriptors and handles non-descriptor + callables as instance methods. + """ + + def __init__(self, func, *args, **keywords): + if not callable(func) and not hasattr(func, "__get__"): + raise TypeError("{!r} is not callable or a descriptor" + .format(func)) + + # func could be a descriptor like classmethod which isn't callable, + # so we can't inherit from partial (it verifies func is callable) + if isinstance(func, partialmethod): + # flattening is mandatory in order to place cls/self before all + # other arguments + # it's also more efficient since only one function will be called + self.func = func.func + self.args = func.args + args + self.keywords = func.keywords.copy() + self.keywords.update(keywords) + else: + self.func = func + self.args = args + self.keywords = keywords + + def __repr__(self): + args = ", ".join(map(repr, self.args)) + keywords = ", ".join("{}={!r}".format(k, v) + for k, v in self.keywords.items()) + format_string = "{module}.{cls}({func}, {args}, {keywords})" + return format_string.format(module=self.__class__.__module__, + cls=self.__class__.__name__, + func=self.func, + args=args, + keywords=keywords) + + def _make_unbound_method(self): + def _method(*args, **keywords): + call_keywords = self.keywords.copy() + call_keywords.update(keywords) + cls_or_self, *rest = args + call_args = (cls_or_self,) + self.args + tuple(rest) + return self.func(*call_args, **call_keywords) + _method.__isabstractmethod__ = self.__isabstractmethod__ + return _method + + def __get__(self, obj, cls): + get = getattr(self.func, "__get__", None) + result = None + if get is not None: + new_func = get(obj, cls) + if new_func is not self.func: + # Assume __get__ returning something new indicates the + # creation of an appropriate callable + result = partial(new_func, *self.args, **self.keywords) + try: + result.__self__ = new_func.__self__ + except AttributeError: + pass + if result is None: + # If the underlying descriptor didn't do anything, treat this + # like an instance method + result = self._make_unbound_method().__get__(obj, cls) + return result + + @property + def __isabstractmethod__(self): + return getattr(self.func, "__isabstractmethod__", False) + ################################################################################ ### LRU Cache function decorator diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py index cb493bf..31c093b 100644 --- a/Lib/test/test_functools.py +++ b/Lib/test/test_functools.py @@ -1,3 +1,4 @@ +import abc import collections from itertools import permutations import pickle @@ -217,6 +218,120 @@ class TestPartialCSubclass(TestPartialC): partial = PartialSubclass +class TestPartialMethod(unittest.TestCase): + + class A(object): + nothing = functools.partialmethod(capture) + positional = functools.partialmethod(capture, 1) + keywords = functools.partialmethod(capture, a=2) + both = functools.partialmethod(capture, 3, b=4) + + nested = functools.partialmethod(positional, 5) + + over_partial = functools.partialmethod(functools.partial(capture, c=6), 7) + + static = functools.partialmethod(staticmethod(capture), 8) + cls = functools.partialmethod(classmethod(capture), d=9) + + a = A() + + def test_arg_combinations(self): + self.assertEqual(self.a.nothing(), ((self.a,), {})) + self.assertEqual(self.a.nothing(5), ((self.a, 5), {})) + self.assertEqual(self.a.nothing(c=6), ((self.a,), {'c': 6})) + self.assertEqual(self.a.nothing(5, c=6), ((self.a, 5), {'c': 6})) + + self.assertEqual(self.a.positional(), ((self.a, 1), {})) + self.assertEqual(self.a.positional(5), ((self.a, 1, 5), {})) + self.assertEqual(self.a.positional(c=6), ((self.a, 1), {'c': 6})) + self.assertEqual(self.a.positional(5, c=6), ((self.a, 1, 5), {'c': 6})) + + self.assertEqual(self.a.keywords(), ((self.a,), {'a': 2})) + self.assertEqual(self.a.keywords(5), ((self.a, 5), {'a': 2})) + self.assertEqual(self.a.keywords(c=6), ((self.a,), {'a': 2, 'c': 6})) + self.assertEqual(self.a.keywords(5, c=6), ((self.a, 5), {'a': 2, 'c': 6})) + + self.assertEqual(self.a.both(), ((self.a, 3), {'b': 4})) + self.assertEqual(self.a.both(5), ((self.a, 3, 5), {'b': 4})) + self.assertEqual(self.a.both(c=6), ((self.a, 3), {'b': 4, 'c': 6})) + self.assertEqual(self.a.both(5, c=6), ((self.a, 3, 5), {'b': 4, 'c': 6})) + + self.assertEqual(self.A.both(self.a, 5, c=6), ((self.a, 3, 5), {'b': 4, 'c': 6})) + + def test_nested(self): + self.assertEqual(self.a.nested(), ((self.a, 1, 5), {})) + self.assertEqual(self.a.nested(6), ((self.a, 1, 5, 6), {})) + self.assertEqual(self.a.nested(d=7), ((self.a, 1, 5), {'d': 7})) + self.assertEqual(self.a.nested(6, d=7), ((self.a, 1, 5, 6), {'d': 7})) + + self.assertEqual(self.A.nested(self.a, 6, d=7), ((self.a, 1, 5, 6), {'d': 7})) + + def test_over_partial(self): + self.assertEqual(self.a.over_partial(), ((self.a, 7), {'c': 6})) + self.assertEqual(self.a.over_partial(5), ((self.a, 7, 5), {'c': 6})) + self.assertEqual(self.a.over_partial(d=8), ((self.a, 7), {'c': 6, 'd': 8})) + self.assertEqual(self.a.over_partial(5, d=8), ((self.a, 7, 5), {'c': 6, 'd': 8})) + + self.assertEqual(self.A.over_partial(self.a, 5, d=8), ((self.a, 7, 5), {'c': 6, 'd': 8})) + + def test_bound_method_introspection(self): + obj = self.a + self.assertIs(obj.both.__self__, obj) + self.assertIs(obj.nested.__self__, obj) + self.assertIs(obj.over_partial.__self__, obj) + self.assertIs(obj.cls.__self__, self.A) + self.assertIs(self.A.cls.__self__, self.A) + + def test_unbound_method_retrieval(self): + obj = self.A + self.assertFalse(hasattr(obj.both, "__self__")) + self.assertFalse(hasattr(obj.nested, "__self__")) + self.assertFalse(hasattr(obj.over_partial, "__self__")) + self.assertFalse(hasattr(obj.static, "__self__")) + self.assertFalse(hasattr(self.a.static, "__self__")) + + def test_descriptors(self): + for obj in [self.A, self.a]: + with self.subTest(obj=obj): + self.assertEqual(obj.static(), ((8,), {})) + self.assertEqual(obj.static(5), ((8, 5), {})) + self.assertEqual(obj.static(d=8), ((8,), {'d': 8})) + self.assertEqual(obj.static(5, d=8), ((8, 5), {'d': 8})) + + self.assertEqual(obj.cls(), ((self.A,), {'d': 9})) + self.assertEqual(obj.cls(5), ((self.A, 5), {'d': 9})) + self.assertEqual(obj.cls(c=8), ((self.A,), {'c': 8, 'd': 9})) + self.assertEqual(obj.cls(5, c=8), ((self.A, 5), {'c': 8, 'd': 9})) + + def test_overriding_keywords(self): + self.assertEqual(self.a.keywords(a=3), ((self.a,), {'a': 3})) + self.assertEqual(self.A.keywords(self.a, a=3), ((self.a,), {'a': 3})) + + def test_invalid_args(self): + with self.assertRaises(TypeError): + class B(object): + method = functools.partialmethod(None, 1) + + def test_repr(self): + self.assertEqual(repr(vars(self.A)['both']), + 'functools.partialmethod({}, 3, b=4)'.format(capture)) + + def test_abstract(self): + class Abstract(abc.ABCMeta): + + @abc.abstractmethod + def add(self, x, y): + pass + + add5 = functools.partialmethod(add, 5) + + self.assertTrue(Abstract.add.__isabstractmethod__) + self.assertTrue(Abstract.add5.__isabstractmethod__) + + for func in [self.A.static, self.A.cls, self.A.over_partial, self.A.nested, self.A.both]: + self.assertFalse(getattr(func, '__isabstractmethod__', False)) + + class TestUpdateWrapper(unittest.TestCase): def check_wrapper(self, wrapper, wrapped, @@ -1433,6 +1548,7 @@ def test_main(verbose=None): TestPartialC, TestPartialPy, TestPartialCSubclass, + TestPartialMethod, TestUpdateWrapper, TestTotalOrdering, TestCmpToKeyC, diff --git a/Misc/NEWS b/Misc/NEWS index 45d8a8a..3099b7f 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -1192,6 +1192,8 @@ Core and Builtins Library ------- +- Issue #4331: Added functools.partialmethod (Initial patch by Alon Horev) + - Issue #13461: Fix a crash in the TextIOWrapper.tell method on 64-bit platforms. Patch by Yogesh Chaudhari. -- cgit v0.12