Add :subscript: option to :py:{function,method}

This can be used to document *subscript methods* and *subscript
functions*, like `arr.vindex[1:2, [3, 4, 5]]`.

Author: jbms

doc/conf.py

@@ -243,6 +243,7 @@
     ('py:exc', 'sphinx.environment.NoUri'),
     ('py:func', 'setup'),
     ('py:func', 'sphinx.util.nodes.nested_parse_with_titles'),
+    ('py:class', 'IndexExpression'),  # doc/usage/domains/python.rst
     # Error in sphinxcontrib.websupport.core::WebSupport.add_comment
     ('py:meth', 'get_comments'),
     ('py:mod', 'autodoc'),

doc/usage/domains/python.rst

@@ -120,6 +120,45 @@ The following directives are provided for module and class contents:
 
       .. versionadded:: 7.1
 
+   .. rst:directive:option:: subscript
+      :type: no value
+
+      Indicate that the function's parameters should be displayed
+      within square brackets instead of parentheses, in order to
+      indicate that it must be invoked as a *subscript function*..
+
+      For example:
+
+      .. code-block:: rst
+
+         .. py:function:: numpy.s_(indexing_expr: tuple[int, ...]) -> IndexExpression
+            :subscript:
+
+            Creates an index expression object.
+
+      This is rendered as:
+
+      .. py:method:: numpy.s_(indexing_expr: tuple[int, ...]) -> IndexExpression
+         :no-contents-entry:
+         :no-index-entry:
+         :subscript:
+
+         Creates an index expression object.
+
+      A *subscript function* can be implemented as follows:
+
+      .. code-block:: python
+
+	 class _S:
+	     @staticmethod
+	     def __getitem__(indexing_expr: tuple[int, ...]) -> IndexExpression:
+		 ...
+
+         s_ = _S()
+
+      .. versionadded:: 8.3
+      
+
 
 .. rst:directive:: .. py:data:: name
 
@@ -516,6 +555,46 @@ The following directives are provided for module and class contents:
 
       .. versionadded:: 2.1
 
+   .. rst:directive:option:: subscript
+      :type: no value
+
+      Indicate that the method's parameters should be displayed within
+      square brackets instead of parentheses, in order to indicate
+      that it must be invoked as a *subscript method*.
+
+      For example:
+
+      .. code-block:: rst
+
+         .. py:method:: Array.vindex(self, indexing_expr: tuple[int, ...]) -> list[int]
+            :subscript:
+
+            Index the array using *vindex* semantics.
+
+      This is rendered as:
+
+      .. py:method:: Array.vindex(self, indexing_expr: tuple[int, ...]) -> list[int]
+         :no-contents-entry:
+         :no-index-entry:
+         :subscript:
+
+         Index the array using *vindex* semantics.
+
+      A *subscript method* can be implemented as follows:
+
+      .. code-block:: python
+
+         class Array:
+             class _Vindex:
+                 def __init__(self, parent: Array):
+                     self.parent = parent
+                 def __getitem__(self, indexing_expr: tuple[int, ...]) -> list[int]:
+                     ...
+             @property
+	     def vindex(self) -> Array._Vindex:
+	         return Array._Vindex(self)
+
+      .. versionadded:: 8.3
 
 .. rst:directive:: .. py:staticmethod:: name(parameters)
                    .. py:staticmethod:: name[type parameters](parameters)

sphinx/addnodes.py

@@ -246,12 +246,20 @@ class desc_parameterlist(nodes.Part, nodes.Inline, nodes.FixedTextElement):
     In that case each parameter will then be written on its own, indented line.
     A trailing comma will be added on the last line
     if ``multi_line_trailing_comma`` is True.
+
+    By default, it is surrounded by parentheses ``("(", ")")``, but this may be
+    overridden by specifying a ``brackets`` attribute.
     """
 
     child_text_separator = ', '
 
+    @property
+    def brackets(self) -> tuple[str, str]:
+        return self.get('brackets', ('(', ')'))
+
     def astext(self) -> str:
-        return f'({super().astext()})'
+        open_punct, close_punct = self.brackets
+        return f'{open_punct}{super().astext()}{close_punct}'
 
 
 class desc_type_parameter_list(nodes.Part, nodes.Inline, nodes.FixedTextElement):

sphinx/domains/python/__init__.py

@@ -88,6 +88,7 @@ class PyFunction(PyObject):
     option_spec: ClassVar[OptionSpec] = PyObject.option_spec.copy()
     option_spec.update({
         'async': directives.flag,
+        'subscript': directives.flag,
     })
 
     def get_signature_prefix(self, sig: str) -> Sequence[nodes.Node]:
@@ -235,6 +236,7 @@ class PyMethod(PyObject):
         'classmethod': directives.flag,
         'final': directives.flag,
         'staticmethod': directives.flag,
+        'subscript': directives.flag,
     })
 
     def needs_arglist(self) -> bool:
@@ -293,6 +295,10 @@ class PyClassMethod(PyMethod):
     """Description of a classmethod."""
 
     option_spec: ClassVar[OptionSpec] = PyObject.option_spec.copy()
+    option_spec.update({
+        'async': directives.flag,
+        'subscript': directives.flag,
+    })
 
     def run(self) -> list[Node]:
         self.name = 'py:method'
@@ -305,6 +311,10 @@ class PyStaticMethod(PyMethod):
     """Description of a staticmethod."""
 
     option_spec: ClassVar[OptionSpec] = PyObject.option_spec.copy()
+    option_spec.update({
+        'async': directives.flag,
+        'subscript': directives.flag,
+    })
 
     def run(self) -> list[Node]:
         self.name = 'py:method'

sphinx/domains/python/_object.py

@@ -384,6 +384,10 @@ def handle_signature(self, sig: str, signode: desc_signature) -> tuple[str, str]
                 # for callables, add an empty parameter list
                 signode += addnodes.desc_parameterlist()
 
+        if 'subscript' in self.options:
+            for node in signode.findall(addnodes.desc_parameterlist):
+                node['brackets'] = '[', ']'
+
         if retann:
             children = _parse_annotation(retann, self.env)
             signode += addnodes.desc_returns(retann, '', *children)

sphinx/texinputs/sphinxlatexobjects.sty

@@ -124,8 +124,8 @@
 \setlength\sphinxsignaturelistskip{0pt}
 \newcommand{\pysigtypelistopen}{\hskip\sphinxsignaturelistskip\sphinxcode{[}}
 \newcommand{\pysigtypelistclose}{\sphinxcode{]}}
-\newcommand{\pysigarglistopen}{\hskip\sphinxsignaturelistskip\sphinxcode{(}}
-\newcommand{\pysigarglistclose}{\sphinxcode{)}}
+\newcommand{\pysigarglistopen}{\hskip\sphinxsignaturelistskip\sphinxcode{\pysigarglistopenpunct}}
+\newcommand{\pysigarglistclose}{\sphinxcode{\pysigarglistclosepunct}}
 %
 % Use a \parbox to accommodate long argument list in signatures
 % LaTeX did not imagine that an \item label could need multi-line rendering

sphinx/writers/html5.py

@@ -186,7 +186,10 @@ def _depart_sig_parameter_list(self, node: Element) -> None:
         self.body.append(f'<span class="sig-paren">{sig_close_paren}</span>')
 
     def visit_desc_parameterlist(self, node: Element) -> None:
-        self._visit_sig_parameter_list(node, addnodes.desc_parameter, '(', ')')
+        open_punct, close_punct = node.brackets  # type: ignore[attr-defined]
+        self._visit_sig_parameter_list(
+            node, addnodes.desc_parameter, open_punct, close_punct
+        )
 
     def depart_desc_parameterlist(self, node: Element) -> None:
         self._depart_sig_parameter_list(node)

sphinx/writers/latex.py

@@ -816,6 +816,16 @@ def depart_desc(self, node: Element) -> None:
         else:
             self.body.append(CR + r'\end{fulllineitems}' + BLANKLINE)
 
+    def _define_parameterlist_brackets(self, open_punct: str, close_punct: str) -> None:
+        self.body.append(
+            r'\def\pysigarglistopenpunct{'
+            + self.escape(open_punct)
+            + '}'
+            + r'\def\pysigarglistclosepunct{'
+            + self.escape(close_punct)
+            + '}'
+        )
+
     def _visit_signature_line(self, node: Element) -> None:
         def next_sibling(e: Node) -> Node | None:
             try:
@@ -837,6 +847,7 @@ def has_multi_line(e: Element) -> bool:
                 if isinstance(arglist, addnodes.desc_parameterlist):
                     # tp_list + arglist: \macro{name}{tp_list}{arglist}{retann}
                     multi_arglist = has_multi_line(arglist)
+                    self._define_parameterlist_brackets(*arglist.brackets)
                 else:
                     # orphan tp_list:    \macro{name}{tp_list}{}{retann}
                     # see: https://github.com/sphinx-doc/sphinx/issues/12543
@@ -867,6 +878,7 @@ def has_multi_line(e: Element) -> bool:
                 break
 
             if isinstance(child, addnodes.desc_parameterlist):
+                self._define_parameterlist_brackets(*child.brackets)
                 # arglist only: \macro{name}{arglist}{retann}
                 if has_multi_line(child):
                     self.body.append(CR + r'\pysigwithonelineperarg' + CR + '{')

sphinx/writers/manpage.py

@@ -188,11 +188,13 @@ def depart_desc_returns(self, node: Element) -> None:
         pass
 
     def visit_desc_parameterlist(self, node: Element) -> None:
-        self.body.append('(')
+        open_punct, _ = node.brackets  # type: ignore[attr-defined]
+        self.body.append(open_punct)
         self.first_param = 1
 
     def depart_desc_parameterlist(self, node: Element) -> None:
-        self.body.append(')')
+        _, close_punct = node.brackets  # type: ignore[attr-defined]
+        self.body.append(close_punct)
 
     def visit_desc_type_parameter_list(self, node: Element) -> None:
         self.body.append('[')

sphinx/writers/texinfo.py

@@ -1480,11 +1480,13 @@ def depart_desc_returns(self, node: Element) -> None:
         pass
 
     def visit_desc_parameterlist(self, node: Element) -> None:
-        self.body.append(' (')
+        open_punct, _ = node.brackets  # type: ignore[attr-defined]
+        self.body.append(f' {open_punct}')
         self.first_param = 1
 
     def depart_desc_parameterlist(self, node: Element) -> None:
-        self.body.append(')')
+        _, close_punct = node.brackets  # type: ignore[attr-defined]
+        self.body.append(close_punct)
 
     def visit_desc_type_parameter_list(self, node: Element) -> None:
         self.body.append(' [')