pandas-dev · mroeschke · Apr 17, 2023 · Sep 9, 2022 · Dec 31, 2022 · Jan 1, 2023
diff --git a/doc/source/reference/groupby.rst b/doc/source/reference/groupby.rst
@@ -7,7 +7,9 @@ GroupBy
 =======
 .. currentmodule:: pandas.core.groupby
 
-GroupBy objects are returned by groupby calls: :func:`pandas.DataFrame.groupby`, :func:`pandas.Series.groupby`, etc.
+:class:`pandas.api.typing.DataFrameGroupBy` and :class:`pandas.api.typing.SeriesGroupBy`
+instances are returned by groupby calls :func:`pandas.DataFrame.groupby` and
+:func:`pandas.Series.groupby` respectively.
 
 Indexing, iteration
 -------------------

diff --git a/doc/source/reference/index.rst b/doc/source/reference/index.rst
@@ -9,11 +9,24 @@ API reference
 This page gives an overview of all public pandas objects, functions and
 methods. All classes and functions exposed in ``pandas.*`` namespace are public.
 
-Some subpackages are public which include ``pandas.errors``,
-``pandas.plotting``, and ``pandas.testing``. Public functions in
-``pandas.io`` and ``pandas.tseries`` submodules are mentioned in
-the documentation. ``pandas.api.types`` subpackage holds some
-public functions related to data types in pandas.
+The following subpackages are public.
+
+ - ``pandas.errors``: Custom exception and warnings classes that are raised by pandas.
+ - ``pandas.plotting``: Plotting public API.
+ - ``pandas.testing``: Functions that are useful for writing tests involving pandas objects.
+ - ``pandas.api.extensions``: Functions and classes for extending pandas objects.
+ - ``pandas.api.indexers``: Functions and classes for rolling window indexers.
+ - ``pandas.api.interchange``: DataFrame interchange protocol.
+ - ``pandas.api.types``: Datatype classes and functions.
+ - ``pandas.api.typing``: Classes that may be necessary for type-hinting. These are
+   classes that are encountered as intermediate results but should not be
+   instantiated  directly by users. These classes are not to be confused with
+   classes from the `pandas-stubs <https://github.com/pandas-dev/pandas-stubs>`_
+   package which has classes in addition to those that occur in pandas for type-hinting.
+
+In addition, public functions in ``pandas.io`` and ``pandas.tseries`` submodules
+are mentioned in the documentation.
+
 
 .. warning::
 

diff --git a/doc/source/reference/resampling.rst b/doc/source/reference/resampling.rst
@@ -7,7 +7,8 @@ Resampling
 ==========
 .. currentmodule:: pandas.core.resample
 
-Resampler objects are returned by resample calls: :func:`pandas.DataFrame.resample`, :func:`pandas.Series.resample`.
+:class:`pandas.api.typing.Resampler` instances are returned by
+resample calls: :func:`pandas.DataFrame.resample`, :func:`pandas.Series.resample`.
 
 Indexing, iteration
 ~~~~~~~~~~~~~~~~~~~

diff --git a/doc/source/reference/window.rst b/doc/source/reference/window.rst
@@ -6,9 +6,12 @@
 Window
 ======
 
-Rolling objects are returned by ``.rolling`` calls: :func:`pandas.DataFrame.rolling` and :func:`pandas.Series.rolling`.
-Expanding objects are returned by ``.expanding`` calls: :func:`pandas.DataFrame.expanding` and :func:`pandas.Series.expanding`.
-ExponentialMovingWindow objects are returned by ``.ewm`` calls: :func:`pandas.DataFrame.ewm` and :func:`pandas.Series.ewm`.
+:class:`pandas.api.typing.Rolling` instances are returned by ``.rolling`` calls:
+:func:`pandas.DataFrame.rolling` and :func:`pandas.Series.rolling`.
+:class:`pandas.api.typing.Expanding` instances are returned by ``.expanding`` calls:
+:func:`pandas.DataFrame.expanding` and :func:`pandas.Series.expanding`.
+:class:`pandas.api.typing.ExponentialMovingWindow` instances are returned by ``.ewm``
+calls: :func:`pandas.DataFrame.ewm` and :func:`pandas.Series.ewm`.
 
 .. _api.functions_rolling:
 

diff --git a/doc/source/user_guide/groupby.rst b/doc/source/user_guide/groupby.rst
@@ -128,6 +128,7 @@ consider the following ``DataFrame``:
    df
 
 On a DataFrame, we obtain a GroupBy object by calling :meth:`~DataFrame.groupby`.
+This method returns a ``pandas.api.typing.DataFrameGroupBy`` instance.
 We could naturally group by either the ``A`` or ``B`` columns, or both:
 
 .. ipython:: python
@@ -1413,8 +1414,9 @@ Groupby a specific column with the desired frequency. This is like resampling.
 
    df.groupby([pd.Grouper(freq="1M", key="Date"), "Buyer"])[["Quantity"]].sum()
 
-You have an ambiguous specification in that you have a named index and a column
-that could be potential groupers.
+When ``freq`` is specified, the object returned by ``pd.Grouper`` will be an
+instance of ``pandas.api.typing.TimeGrouper``. You have an ambiguous specification
+in that you have a named index and a column that could be potential groupers.
 
 .. ipython:: python
 

diff --git a/doc/source/user_guide/io.rst b/doc/source/user_guide/io.rst
@@ -2069,7 +2069,7 @@ is ``None``. To explicitly force ``Series`` parsing, pass ``typ=series``
   seconds, milliseconds, microseconds or nanoseconds respectively.
 * ``lines`` : reads file as one json object per line.
 * ``encoding`` : The encoding to use to decode py3 bytes.
-* ``chunksize`` : when used in combination with ``lines=True``, return a JsonReader which reads in ``chunksize`` lines per iteration.
+* ``chunksize`` : when used in combination with ``lines=True``, return a ``pandas.api.typing.JsonReader`` which reads in ``chunksize`` lines per iteration.
 * ``engine``: Either ``"ujson"``, the built-in JSON parser, or ``"pyarrow"`` which dispatches to pyarrow's ``pyarrow.json.read_json``.
   The ``"pyarrow"`` is only available when ``lines=True``
 
@@ -5984,15 +5984,15 @@ Reading from Stata format
 '''''''''''''''''''''''''
 
 The top-level function ``read_stata`` will read a dta file and return
-either a ``DataFrame`` or a :class:`~pandas.io.stata.StataReader` that can
+either a ``DataFrame`` or a :class:`pandas.api.typing.StataReader` that can
 be used to read the file incrementally.
 
 .. ipython:: python
 
    pd.read_stata("stata.dta")
 
 Specifying a ``chunksize`` yields a
-:class:`~pandas.io.stata.StataReader` instance that can be used to
+:class:`pandas.api.typing.StataReader` instance that can be used to
 read ``chunksize`` lines from the file at a time.  The ``StataReader``
 object can be used as an iterator.
 

diff --git a/doc/source/user_guide/timeseries.rst b/doc/source/user_guide/timeseries.rst
@@ -1750,8 +1750,9 @@ We can instead only resample those groups where we have points as follows:
 Aggregation
 ~~~~~~~~~~~
 
-Similar to the :ref:`aggregating API <basics.aggregate>`, :ref:`groupby API <groupby.aggregate>`, and the :ref:`window API <window.overview>`,
-a ``Resampler`` can be selectively resampled.
+The ``resample()`` method returns a ``pandas.api.typing.Resampler`` instance.  Similar to
+the :ref:`aggregating API <basics.aggregate>`, :ref:`groupby API <groupby.aggregate>`,
+and the :ref:`window API <window.overview>`, a ``Resampler`` can be selectively resampled.
 
 Resampling a ``DataFrame``, the default will be to act on all columns with the same function.
 

diff --git a/doc/source/user_guide/window.rst b/doc/source/user_guide/window.rst
@@ -37,14 +37,14 @@ pandas supports 4 types of windowing operations:
 #. Expanding window: Accumulating window over the values.
 #. Exponentially Weighted window: Accumulating and exponentially weighted window over the values.
 
-=============================   =================  ===========================   ===========================  ========================  ===================================  ===========================
-Concept                         Method             Returned Object               Supports time-based windows  Supports chained groupby  Supports table method                Supports online operations
-=============================   =================  ===========================   ===========================  ========================  ===================================  ===========================
-Rolling window                  ``rolling``        ``Rolling``                   Yes                          Yes                       Yes (as of version 1.3)              No
-Weighted window                 ``rolling``        ``Window``                    No                           No                        No                                   No
-Expanding window                ``expanding``      ``Expanding``                 No                           Yes                       Yes (as of version 1.3)              No
-Exponentially Weighted window   ``ewm``            ``ExponentialMovingWindow``   No                           Yes (as of version 1.2)   No                                   Yes (as of version 1.3)
-=============================   =================  ===========================   ===========================  ========================  ===================================  ===========================
+=============================   =================  =============================================   ===========================  ========================  ===================================  ===========================
+Concept                         Method             Returned Object                                 Supports time-based windows  Supports chained groupby  Supports table method                Supports online operations
+=============================   =================  =============================================   ===========================  ========================  ===================================  ===========================
+Rolling window                  ``rolling``        ``pandas.typing.api.Rolling``                   Yes                          Yes                       Yes (as of version 1.3)              No
+Weighted window                 ``rolling``        ``pandas.typing.api.Window``                    No                           No                        No                                   No
+Expanding window                ``expanding``      ``pandas.typing.api.Expanding``                 No                           Yes                       Yes (as of version 1.3)              No
+Exponentially Weighted window   ``ewm``            ``pandas.typing.api.ExponentialMovingWindow``   No                           Yes (as of version 1.2)   No                                   Yes (as of version 1.3)
+=============================   =================  =============================================   ===========================  ========================  ===================================  ===========================
 
 As noted above, some operations support specifying a window based on a time offset:
 

diff --git a/doc/source/whatsnew/v2.1.0.rst b/doc/source/whatsnew/v2.1.0.rst
@@ -75,6 +75,7 @@ Other enhancements
   :meth:`Categorical.map` implicitly had a default value of ``"ignore"`` for ``na_action``. This has formally been deprecated and will be changed to ``None`` in the future.
   Also notice that :meth:`Series.map` has default ``na_action=None`` and calls to series with categorical data will now use ``na_action=None`` unless explicitly set otherwise (:issue:`44279`)
 - Implemented ``__pandas_priority__`` to allow custom types to take precedence over :class:`DataFrame`, :class:`Series`, :class:`Index`, or :class:`ExtensionArray` for arithmetic operations, :ref:`see the developer guide <extending.pandas_priority>` (:issue:`48347`)
+- Classes that are useful for type-hinting have been added to the public API in the new submodule ``pandas.api.typing`` (:issue:`48577`)
 - :meth:`MultiIndex.sort_values` now supports ``na_position`` (:issue:`51612`)
 - :meth:`MultiIndex.sortlevel` and :meth:`Index.sortlevel` gained a new keyword ``na_position`` (:issue:`51612`)
 - :meth:`arrays.DatetimeArray.map`, :meth:`arrays.TimedeltaArray.map` and :meth:`arrays.PeriodArray.map` can now take a ``na_action`` argument (:issue:`51644`)

diff --git a/pandas/api/__init__.py b/pandas/api/__init__.py
@@ -4,11 +4,13 @@
     indexers,
     interchange,
     types,
+    typing,
 )
 
 __all__ = [
     "interchange",
     "extensions",
     "indexers",
     "types",
+    "typing",
 ]
diff --git a/pandas/api/typing/__init__.py b/pandas/api/typing/__init__.py
@@ -0,0 +1,50 @@
+"""
+Public API classes that store intermediate results useful for type-hinting.
+"""
+
+from pandas.core.groupby import (
+    DataFrameGroupBy,
+    SeriesGroupBy,
+)
+from pandas.core.resample import (
+    DatetimeIndexResamplerGroupby,
+    PeriodIndexResamplerGroupby,
+    Resampler,
+    TimedeltaIndexResamplerGroupby,
+    TimeGrouper,
+)
+from pandas.core.window import (
+    Expanding,
+    ExpandingGroupby,
+    ExponentialMovingWindow,
+    ExponentialMovingWindowGroupby,
+    Rolling,
+    RollingGroupby,
+    Window,
+)
+
+# TODO: Can't import Styler without importing jinja2
+# from pandas.io.formats.style import Styler
+from pandas.io.json._json import JsonReader
+from pandas.io.stata import StataReader
+
+__all__ = [
+    "DataFrameGroupBy",
+    "DatetimeIndexResamplerGroupby",
+    "Expanding",
+    "ExpandingGroupby",
+    "ExponentialMovingWindow",
+    "ExponentialMovingWindowGroupby",
+    "JsonReader",
+    "PeriodIndexResamplerGroupby",
+    "Resampler",
+    "Rolling",
+    "RollingGroupby",
+    "SeriesGroupBy",
+    "StataReader",
+    # See TODO above
+    # "Styler",
+    "TimedeltaIndexResamplerGroupby",
+    "TimeGrouper",
+    "Window",
+]
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
@@ -8699,7 +8699,7 @@ def resample(
 
         Returns
         -------
-        pandas.core.Resampler
+        pandas.api.typing.Resampler
             :class:`~pandas.core.Resampler` object.
 
         See Also

@@ -2618,8 +2618,11 @@ def resample(self, rule, *args, **kwargs):
 
         Returns
         -------
-        Grouper
-            Return a new grouper with our resampler appended.
+        pandas.api.typing.DatetimeIndexResamplerGroupby,
+        pandas.api.typing.PeriodIndexResamplerGroupby, or
+        pandas.api.typing.TimedeltaIndexResamplerGroupby
+            Return a new groupby object, with type depending on the data
+            being resampled.
 
         See Also
         --------
@@ -2783,7 +2786,7 @@ def rolling(self, *args, **kwargs) -> RollingGroupby:
 
         Returns
         -------
-        RollingGroupby
+        pandas.api.typing.RollingGroupby
             Return a new grouper with our rolling appended.
 
         See Also
@@ -2846,6 +2849,10 @@ def expanding(self, *args, **kwargs) -> ExpandingGroupby:
         """
         Return an expanding grouper, providing expanding
         functionality per group.
+
+        Returns
+        -------
+        pandas.api.typing.ExpandingGroupby
         """
         from pandas.core.window import ExpandingGroupby
 
@@ -2862,6 +2869,10 @@ def expanding(self, *args, **kwargs) -> ExpandingGroupby:
     def ewm(self, *args, **kwargs) -> ExponentialMovingWindowGroupby:
         """
         Return an ewm grouper, providing ewm functionality per group.
+
+        Returns
+        -------
+        pandas.api.typing.ExponentialMovingWindowGroupby
         """
         from pandas.core.window import ExponentialMovingWindowGroupby
 

@@ -120,7 +120,9 @@ class Grouper:
 
     Returns
     -------
-    A specification for a groupby instruction
+    Grouper or pandas.api.typing.TimeGrouper
+        A TimeGrouper is returned if ``freq`` is not ``None``. Otherwise, a Grouper
+        is returned.
 
     Examples
     --------

diff --git a/pandas/core/shared_docs.py b/pandas/core/shared_docs.py
@@ -178,7 +178,7 @@
 
 Returns
 -------
-%(klass)sGroupBy
+pandas.api.typing.%(klass)sGroupBy
     Returns a groupby object that contains information about the groups.
 
 See Also

diff --git a/pandas/core/window/ewm.py b/pandas/core/window/ewm.py
@@ -231,7 +231,7 @@ class ExponentialMovingWindow(BaseWindow):
 
     Returns
     -------
-    ``ExponentialMovingWindow`` subclass
+    pandas.api.typing.ExponentialMovingWindow
 
     See Also
     --------

diff --git a/pandas/core/window/expanding.py b/pandas/core/window/expanding.py
@@ -72,7 +72,7 @@ class Expanding(RollingAndExpandingMixin):
 
     Returns
     -------
-    ``Expanding`` subclass
+    pandas.api.typing.Expanding
 
     See Also
     --------

diff --git a/pandas/core/window/rolling.py b/pandas/core/window/rolling.py
@@ -965,9 +965,9 @@ class Window(BaseWindow):
 
     Returns
     -------
-    ``Window`` subclass if a ``win_type`` is passed
-
-    ``Rolling`` subclass if ``win_type`` is not passed
+    pandas.api.typing.Window or pandas.api.typing.Rolling
+        An instance of Window is returned if ``win_type`` is passed. Otherwise,
+        an instance of Rolling is returned.
 
     See Also
     --------

diff --git a/pandas/io/json/_json.py b/pandas/io/json/_json.py
@@ -665,8 +665,9 @@ def read_json(
 
     Returns
     -------
-    Series or DataFrame
-        The type returned depends on the value of `typ`.
+    Series, DataFrame, or pandas.api.typing.JsonReader
+        A JsonReader is returned when ``chunksize`` is not ``0`` or ``None``.
+        Otherwise, the type returned depends on the value of ``typ``.
 
     See Also
     --------

diff --git a/pandas/io/stata.py b/pandas/io/stata.py
@@ -156,7 +156,7 @@
 
 Returns
 -------
-DataFrame or StataReader
+DataFrame or pandas.api.typing.StataReader
 
 See Also
 --------

diff --git a/pandas/tests/api/test_api.py b/pandas/tests/api/test_api.py
@@ -236,7 +236,7 @@ def test_depr(self):
 
 
 class TestApi(Base):
-    allowed = ["types", "extensions", "indexers", "interchange"]
+    allowed = ["types", "extensions", "indexers", "interchange", "typing"]
 
     def test_api(self):
         self.check(api, self.allowed)
-Original file line number
+Diff line change
@@ Expand Up / @@ -231,7 +231,7 @@ class ExponentialMovingWindow(BaseWindow): @@
         Returns
         -------
-        ``ExponentialMovingWindow`` subclass
+        pandas.api.typing.ExponentialMovingWindow
         See Also
         --------
@@ Expand Down @@