Sep 26, 2024 · May 21, 2024 · May 21, 2024 · May 21, 2024 · May 21, 2024 · May 21, 2024
diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst
      >>> basetwo('10010')
      18

   If ``Placeholder`` sentinels are present in *args*, they will be filled first
   when :func:`partial` is called. This allows custom selection of positional arguments
   to be pre-filled when constructing :ref:`partial object<partial-objects>`.
   If ``Placeholder`` sentinels are used, all of them must be filled at call time.:

      >>> from functools import partial, Placeholder
      >>> say_to_world = partial(print, Placeholder, 'world!')
      >>> say_to_world('Hello')
      Hello world!

   .. versionchanged:: 3.14
      Support for ``Placeholder`` in *args*

 .. class:: partialmethod(func, /, *args, **keywords)

diff --git a/Lib/functools.py b/Lib/functools.py
 ### partial() argument application
 ################################################################################


 class Placeholder:
    """placeholder for partial arguments"""


 # Purely functional, no descriptor behaviour
 class partial:
    """New function with partial application of the given arguments
        if not callable(func):
            raise TypeError("the first argument must be callable")

        np = 0
        nargs = len(args)
        if args:
            while nargs and args[nargs-1] is Placeholder:
                nargs -= 1
            args = args[:nargs]
            np = args.count(Placeholder)
        if isinstance(func, partial):
            args = func.args + args
            pargs = func.args
            pnp = func.np
            if pnp and args:
                all_args = list(pargs)
                nargs = len(args)
                j, pos = 0, 0
                end = nargs if nargs < pnp else pnp
                while j < end:
                    pos = all_args.index(Placeholder, pos)
                    all_args[pos] = args[j]
                    j += 1
                    pos += 1
                if pnp < nargs:
                    all_args.extend(args[pnp:])
                np += pnp - end
                args = tuple(all_args)
            else:
                np += pnp
                args = func.args + args
            keywords = {**func.keywords, **keywords}
            func = func.func

        self.func = func
        self.args = args
        self.keywords = keywords
        self.np = np
        return self

    def __call__(self, /, *args, **keywords):
        keywords = {**self.keywords, **keywords}
        return self.func(*self.args, *args, **keywords)
        if not hasattr(self, 'np'):
            self.np = self.args.count(Placeholder)
        if np := self.np:
            if len(args) < np:
                raise TypeError("unfilled placeholders in 'partial' call")
            f_args = list(self.args)
            j, pos = 0, 0
            while j < np:
                pos = f_args.index(Placeholder, pos)
                f_args[pos] = args[j]
                j += 1
                pos += 1
            keywords = {**self.keywords, **keywords}
            return self.func(*f_args, *args[np:], **keywords)
        else:
            keywords = {**self.keywords, **keywords}
            return self.func(*self.args, *args, **keywords)

    @recursive_repr()
    def __repr__(self):
        self.keywords = kwds

 try:
    from _functools import partial
    from _functools import partial, Placeholder
 except ImportError:
    pass

diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
        p2.new_attr = 'spam'
        self.assertEqual(p2.new_attr, 'spam')

    def test_placeholders_trailing_trim(self):
        PH = self.module.Placeholder
        for args in [(PH,), (PH, 0), (0, PH), (0, PH, 1, PH, PH, PH)]:
            expected, n = tuple(args), len(args)
            while n and args[n-1] is PH:
                n -= 1
            expected = expected[:n]
            p = self.partial(capture, *args)
            self.assertTrue(p.args == expected)

    def test_placeholders(self):
        PH = self.module.Placeholder
        # 1 Placeholder
        args = (PH, 0)
        p = self.partial(capture, *args)
        got, empty = p('x')
        self.assertTrue(('x', 0) == got and empty == {})
        # 2 Placeholders
        args = (PH, 0, PH, 1)
        p = self.partial(capture, *args)
        with self.assertRaises(TypeError):
            got, empty = p('x')
        got, empty = p('x', 'y')
        expected = ('x', 0, 'y', 1)
        self.assertTrue(expected == got and empty == {})

    def test_placeholders_optimization(self):
        PH = self.module.Placeholder
        p = self.partial(capture, PH, 0)
        p2 = self.partial(p, PH, 1, 2, 3)
        expected = (PH, 0, 1, 2, 3)
        self.assertTrue(expected == p2.args)
        p3 = self.partial(p2, -1, 4)
        got, empty = p3(5)
        expected = (-1, 0, 1, 2, 3, 4, 5)
        self.assertTrue(expected == got and empty == {})

    def test_repr(self):
        args = (object(), object())
        args_repr = ', '.join(repr(a) for a in args)
diff --git a/Misc/NEWS.d/next/Library/2024-05-25-00-54-26.gh-issue-119127.LpPvag.rst b/Misc/NEWS.d/next/Library/2024-05-25-00-54-26.gh-issue-119127.LpPvag.rst
 ``partial`` of ``functools`` module now supports placeholders for positional
 arguments.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -358,6 +358,18 @@ The :mod:`functools` module defines the following functions:
		>>> basetwo('10010')
		18

		If ``Placeholder`` sentinels are present in args, they will be filled first
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		when :func:`partial` is called. This allows custom selection of positional arguments
		to be pre-filled when constructing :ref:`partial object<partial-objects>`.
		If ``Placeholder`` sentinels are used, all of them must be filled at call time.:
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		>>> from functools import partial, Placeholder
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		>>> say_to_world = partial(print, Placeholder, 'world!')
		>>> say_to_world('Hello')
		Hello world!

		.. versionchanged:: 3.14
		Support for ``Placeholder`` in args
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		.. class:: partialmethod(func, /, args, *keywords)

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -273,6 +273,11 @@ def reduce(function, sequence, initial=_initial_missing):
		### partial() argument application
		################################################################################


		class Placeholder:
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		"""placeholder for partial arguments"""


		# Purely functional, no descriptor behaviour
		class partial:
		"""New function with partial application of the given arguments
Expand All		@@ -285,8 +290,33 @@ def __new__(cls, func, /, args, *keywords):
		if not callable(func):
		raise TypeError("the first argument must be callable")

		np = 0
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		nargs = len(args)
		if args:
		while nargs and args[nargs-1] is Placeholder:
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		nargs -= 1
		args = args[:nargs]
		np = args.count(Placeholder)
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		if isinstance(func, partial):
		args = func.args + args
		pargs = func.args
		pnp = func.np
		if pnp and args:
		all_args = list(pargs)
		nargs = len(args)
		j, pos = 0, 0
		end = nargs if nargs < pnp else pnp
		while j < end:
		pos = all_args.index(Placeholder, pos)
		all_args[pos] = args[j]
		j += 1
		pos += 1
		if pnp < nargs:
		all_args.extend(args[pnp:])
		np += pnp - end
		args = tuple(all_args)
		else:
		np += pnp
		args = func.args + args
		keywords = {func.keywords, keywords}
		func = func.func

Expand All		@@ -295,11 +325,27 @@ def __new__(cls, func, /, args, *keywords):
		self.func = func
		self.args = args
		self.keywords = keywords
		self.np = np
		return self

		def __call__(self, /, args, *keywords):
		keywords = {self.keywords, keywords}
		return self.func(self.args, args, **keywords)
		if not hasattr(self, 'np'):
		self.np = self.args.count(Placeholder)
		if np := self.np:
		if len(args) < np:
		raise TypeError("unfilled placeholders in 'partial' call")
		f_args = list(self.args)
		j, pos = 0, 0
		while j < np:
		pos = f_args.index(Placeholder, pos)
		f_args[pos] = args[j]
		j += 1
		pos += 1
		keywords = {self.keywords, keywords}
		return self.func(f_args, args[np:], **keywords)
		else:
		keywords = {self.keywords, keywords}
		return self.func(self.args, args, **keywords)

		@recursive_repr()
		def __repr__(self):
Expand DownExpand Up		@@ -340,7 +386,7 @@ def __setstate__(self, state):
		self.keywords = kwds

		try:
		from _functools import partial
		from _functools import partial, Placeholder
		except ImportError:
		pass

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -210,6 +210,43 @@ def foo(bar):
		p2.new_attr = 'spam'
		self.assertEqual(p2.new_attr, 'spam')

		def test_placeholders_trailing_trim(self):
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		PH = self.module.Placeholder
		for args in [(PH,), (PH, 0), (0, PH), (0, PH, 1, PH, PH, PH)]:
		expected, n = tuple(args), len(args)
		while n and args[n-1] is PH:
		n -= 1
		expected = expected[:n]
		p = self.partial(capture, *args)
		self.assertTrue(p.args == expected)

		def test_placeholders(self):
		PH = self.module.Placeholder
		# 1 Placeholder
		args = (PH, 0)
		p = self.partial(capture, *args)
		got, empty = p('x')
		self.assertTrue(('x', 0) == got and empty == {})
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		# 2 Placeholders
		args = (PH, 0, PH, 1)
		p = self.partial(capture, *args)
		with self.assertRaises(TypeError):
		got, empty = p('x')
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		got, empty = p('x', 'y')
		expected = ('x', 0, 'y', 1)
		self.assertTrue(expected == got and empty == {})
Copy link Member picnixzAug 12, 2024 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Ditto

		def test_placeholders_optimization(self):
		PH = self.module.Placeholder
		p = self.partial(capture, PH, 0)
		p2 = self.partial(p, PH, 1, 2, 3)
		expected = (PH, 0, 1, 2, 3)
		self.assertTrue(expected == p2.args)
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		p3 = self.partial(p2, -1, 4)
		got, empty = p3(5)
		expected = (-1, 0, 1, 2, 3, 4, 5)
		self.assertTrue(expected == got and empty == {})

		def test_repr(self):
		args = (object(), object())
		args_repr = ', '.join(repr(a) for a in args)
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		``partial`` of ``functools`` module now supports placeholders for positional
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		arguments.