gh-142041: Improve concurrent.interpreters documentation

- Add complete Queue method documentation (put, get, empty, full, qsize,
  maxsize, put_nowait, get_nowait) with parameter descriptions
- Expand prepare_main docs explaining its purpose with an example
- Fix exec() signature (remove incorrect dedent parameter)
- Add detailed exec() and call() descriptions with error handling info
- Expand call_in_thread docs explaining thread behavior
- Document create_queue parameters (maxsize, unbounditems)
- Add is_shareable() function documentation
- Rewrite Basic usage section with clearer examples for exec, call,
  prepare_main, queues, and parallel execution patterns
- Add tip pointing to InterpreterPoolExecutor for simpler use cases

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mvanhorn

Doc/library/concurrent.interpreters.rst

@@ -224,11 +224,25 @@ This module defines the following functions:
    Initialize a new (idle) Python interpreter
    and return a :class:`Interpreter` object for it.
 
-.. function:: create_queue()
+.. function:: create_queue(maxsize=0, *, unbounditems=UNBOUND)
 
    Initialize a new cross-interpreter queue and return a :class:`Queue`
    object for it.
 
+   *maxsize* sets the upper bound on the number of items that can be placed
+   in the queue.  If *maxsize* is less than or equal to zero, the queue
+   size is infinite.
+
+   *unbounditems* sets the default behavior when getting an item from the
+   queue whose original interpreter has been destroyed.
+   See :meth:`Queue.put` for supported values.
+
+.. function:: is_shareable(obj)
+
+   Return ``True`` if the object can be sent to another interpreter
+   without using :mod:`pickle`, and ``False`` otherwise.
+   See :ref:`interp-object-sharing`.
+
 
 Interpreter objects
 ^^^^^^^^^^^^^^^^^^^
@@ -261,27 +275,71 @@ Interpreter objects
 
       Finalize and destroy the interpreter.
 
-   .. method:: prepare_main(ns=None, **kwargs)
+   .. method:: prepare_main(ns=None, /, **kwargs)
+
+      Bind the given objects into the interpreter's :mod:`!__main__`
+      module namespace.  This is the primary way to pass data to code
+      running in another interpreter.
+
+      *ns* is an optional :class:`dict` mapping names to values.
+      Any additional keyword arguments are also bound as names.
+
+      The values must be shareable between interpreters.  Some objects
+      are actually shared, some are copied efficiently, and most are
+      copied via :mod:`pickle`.  See :ref:`interp-object-sharing`.
 
-      Bind objects in the interpreter's :mod:`!__main__` module.
+      For example::
 
-      Some objects are actually shared and some are copied efficiently,
-      but most are copied via :mod:`pickle`.  See :ref:`interp-object-sharing`.
+         interp = interpreters.create()
+         interp.prepare_main(name='world')
+         interp.exec('print(f"Hello, {name}!")')
 
-   .. method:: exec(code, /, dedent=True)
+      This is equivalent to setting variables in the interpreter's
+      :mod:`!__main__` module before calling :meth:`exec` or :meth:`call`.
+      The names are available as global variables in the executed code.
+
+   .. method:: exec(code, /)
 
       Run the given source code in the interpreter (in the current thread).
 
+      *code* is a :class:`str` of Python source code.  It is executed as
+      though it were the body of a script, using the interpreter's
+      :mod:`!__main__` module as the globals namespace.
+
+      There is no return value.  To get a result back, use :meth:`call`
+      instead, or communicate through a :class:`Queue`.
+
+      If the code raises an unhandled exception, an :exc:`ExecutionFailed`
+      exception is raised in the calling interpreter.  The actual
+      exception object is not preserved because objects cannot be shared
+      between interpreters directly.
+
+      This blocks the current thread until the code finishes.
+
    .. method:: call(callable, /, *args, **kwargs)
 
-      Return the result of calling running the given function in the
-      interpreter (in the current thread).
+      Call *callable* in the interpreter (in the current thread) and
+      return the result.
+
+      Nearly all callables, args, kwargs, and return values are supported.
+      All "shareable" objects are supported, as are "stateless" functions
+      (meaning non-closures that do not use any globals).  For other
+      objects, this method falls back to :mod:`pickle`.
+
+      If the callable raises an exception, an :exc:`ExecutionFailed`
+      exception is raised in the calling interpreter.
 
    .. _interp-call-in-thread:
 
    .. method:: call_in_thread(callable, /, *args, **kwargs)
 
-      Run the given function in the interpreter (in a new thread).
+      Start a new :class:`~threading.Thread` that calls *callable* in
+      the interpreter and return the thread object.
+
+      This is a convenience wrapper that combines
+      :mod:`threading` with :meth:`call`.  The thread is started
+      immediately.  Call :meth:`~threading.Thread.join` on the returned
+      thread to wait for it to finish.
 
 Exceptions
 ^^^^^^^^^^
@@ -318,19 +376,86 @@ Communicating Between Interpreters
 
 .. class:: Queue(id)
 
-   A wrapper around a low-level, cross-interpreter queue, which
-   implements the :class:`queue.Queue` interface.  The underlying queue
-   can only be created through :func:`create_queue`.
+   A cross-interpreter queue that can be used to pass data safely
+   between interpreters.  It provides the same interface as
+   :class:`queue.Queue`.  The underlying queue can only be created
+   through :func:`create_queue`.
+
+   When an object is placed in the queue, it is prepared for use in
+   another interpreter.  Some objects are actually shared and some are
+   copied efficiently, but most are copied via :mod:`pickle`.
+   See :ref:`interp-object-sharing`.
 
-   Some objects are actually shared and some are copied efficiently,
-   but most are copied via :mod:`pickle`.  See :ref:`interp-object-sharing`.
+   :class:`Queue` objects themselves are shareable between interpreters
+   (they reference the same underlying queue), making them suitable for
+   use with :meth:`Interpreter.prepare_main`.
 
    .. attribute:: id
 
       (read-only)
 
       The queue's ID.
 
+   .. attribute:: maxsize
+
+      (read-only)
+
+      The maximum number of items allowed in the queue.  A value of zero
+      means the queue size is infinite.
+
+   .. method:: empty()
+
+      Return ``True`` if the queue is empty, ``False`` otherwise.
+
+   .. method:: full()
+
+      Return ``True`` if the queue is full, ``False`` otherwise.
+
+   .. method:: qsize()
+
+      Return the number of items in the queue.
+
+   .. method:: put(obj, block=True, timeout=None, *, unbounditems=None)
+
+      Put *obj* into the queue.  If *block* is true (the default),
+      block if necessary until a free slot is available.  If *timeout*
+      is a positive number, block at most *timeout* seconds and raise
+      :exc:`QueueFullError` if no free slot is available within that time.
+
+      If *block* is false, put *obj* in the queue if a free slot is
+      immediately available, otherwise raise :exc:`QueueFullError`.
+
+      *unbounditems* controls what happens when the item is retrieved
+      via :meth:`get` after the interpreter that called :meth:`put` has
+      been destroyed.  If ``None`` (the default), the queue's default
+      (set via :func:`create_queue`) is used.  Supported values:
+
+      * :data:`UNBOUND` -- :meth:`get` returns the :data:`UNBOUND`
+        sentinel in place of the original object.
+      * :data:`UNBOUND_ERROR` -- :meth:`get` raises
+        :exc:`ItemInterpreterDestroyed`.
+      * :data:`UNBOUND_REMOVE` -- the item is silently removed from
+        the queue when the original interpreter is destroyed.
+
+   .. method:: put_nowait(obj, *, unbounditems=None)
+
+      Equivalent to ``put(obj, block=False)``.
+
+   .. method:: get(block=True, timeout=None)
+
+      Remove and return an item from the queue.  If *block* is true
+      (the default), block if necessary until an item is available.
+      If *timeout* is a positive number, block at most *timeout* seconds
+      and raise :exc:`QueueEmptyError` if no item is available within
+      that time.
+
+      If *block* is false, return an item if one is immediately
+      available, otherwise raise :exc:`QueueEmptyError`.
+
+   .. method:: get_nowait()
+
+      Equivalent to ``get(block=False)``.
+
 
 .. exception:: QueueEmptyError
 
@@ -354,31 +479,75 @@ Creating an interpreter and running code in it::
 
     interp = interpreters.create()
 
-    # Run in the current OS thread.
+    # Run source code directly.
+    interp.exec('print("Hello from a subinterpreter!")')
 
-    interp.exec('print("spam!")')
+    # Call a function and get the result.
+    def add(x, y):
+        return x + y
 
-    interp.exec("""if True:
-        print('spam!')
-        """)
+    result = interp.call(add, 3, 4)
+    print(result)  # 7
 
-    from textwrap import dedent
-    interp.exec(dedent("""
-        print('spam!')
-        """))
+    # Run a function in a new thread.
+    def worker():
+        print('Running in a thread!')
 
-    def run(arg):
-        return arg
+    t = interp.call_in_thread(worker)
+    t.join()
 
-    res = interp.call(run, 'spam!')
-    print(res)
+Passing data with :meth:`~Interpreter.prepare_main`::
 
-    def run():
-        print('spam!')
+    interp = interpreters.create()
 
-    interp.call(run)
+    # Bind variables into the interpreter's __main__ namespace.
+    interp.prepare_main(greeting='Hello', name='world')
+    interp.exec('print(f"{greeting}, {name}!")')
 
-    # Run in new OS thread.
+    # Can also use a dict.
+    config = {'host': 'localhost', 'port': 8080}
+    interp.prepare_main(config)
+    interp.exec('print(f"Connecting to {host}:{port}")')
 
-    t = interp.call_in_thread(run)
-    t.join()
+Using queues to communicate between interpreters::
+
+    interp = interpreters.create()
+
+    # Create a queue and share it with the subinterpreter.
+    queue = interpreters.create_queue()
+    interp.prepare_main(queue=queue)
+
+    # The subinterpreter puts results into the queue.
+    interp.exec("""
+    import math
+    queue.put(math.factorial(10))
+    """)
+
+    # The main interpreter reads from the same queue.
+    result = queue.get()
+    print(result)  # 3628800
+
+Running CPU-bound work in parallel using threads and interpreters::
+
+    import time
+    from concurrent import interpreters
+
+    def compute(n):
+        total = sum(range(n))
+        return total
+
+    interp1 = interpreters.create()
+    interp2 = interpreters.create()
+
+    # Each interpreter runs in its own thread and does not share
+    # the GIL, enabling true parallel execution.
+    t1 = interp1.call_in_thread(compute, 50_000_000)
+    t2 = interp2.call_in_thread(compute, 50_000_000)
+    t1.join()
+    t2.join()
+
+.. tip::
+
+   For many use cases, :class:`~concurrent.futures.InterpreterPoolExecutor`
+   provides a higher-level interface that combines threads with
+   interpreters automatically.

Misc/NEWS.d/next/Documentation/2026-03-08-00-00-00.gh-issue-142041.Ab6Luz.rst

@@ -0,0 +1,6 @@
+Improve :mod:`concurrent.interpreters` documentation with clearer
+descriptions of :class:`~concurrent.interpreters.Queue` methods,
+:meth:`~concurrent.interpreters.Interpreter.prepare_main` usage,
+:meth:`~concurrent.interpreters.Interpreter.exec` parameters,
+and expanded usage examples. Also fix the ``exec`` signature which
+incorrectly listed a ``dedent`` parameter.