PERF/REF: make window/groupby imports lazy

pandas/__init__.py

@@ -98,11 +98,9 @@
     to_timedelta,
     # misc
     Flags,
-    Grouper,
     factorize,
     unique,
     value_counts,
-    NamedAgg,
     array,
     Categorical,
     set_eng_float_format,
@@ -184,6 +182,22 @@
 del get_versions, v
 
 
+def __getattr__(name: str):
+    # Lazify imports to speed "import pandas as pd"
+    if name in ("Grouper", "NamedAgg"):
+        from pandas.core import groupby
+
+        return getattr(groupby, name)
+    raise AttributeError(f"module 'pandas' has no attribute '{name}'")
+
+
+def __dir__() -> list[str]:
+    # include lazy imports defined in __getattr__ in dir()
+    base = list(globals().keys())
+    result = base + ["Grouper", "NamedAgg"]
+    return result
+
+
 # module level doc-string
 __doc__ = """
 pandas - a powerful data analysis and manipulation library for Python
@@ -243,7 +257,7 @@
     "Flags",
     "Float32Dtype",
     "Float64Dtype",
-    "Grouper",
+    "Grouper",  # pyright: ignore[reportUnsupportedDunderAll]  # pylint: disable=undefined-all-variable  # noqa:E501
     "HDFStore",
     "Index",
     "IndexSlice",
@@ -257,7 +271,7 @@
     "MultiIndex",
     "NA",
     "NaT",
-    "NamedAgg",
+    "NamedAgg",  # pyright: ignore[reportUnsupportedDunderAll]  # pylint: disable=undefined-all-variable  # noqa:E501
     "Period",
     "PeriodDtype",
     "PeriodIndex",

pandas/core/generic.py

@@ -93,7 +93,10 @@
     SettingWithCopyError,
     SettingWithCopyWarning,
 )
-from pandas.util._decorators import doc
+from pandas.util._decorators import (
+    Appender,
+    doc,
+)
 from pandas.util._exceptions import find_stack_level
 from pandas.util._validators import (
     check_dtype_backend,
@@ -177,14 +180,13 @@
     find_valid_index,
 )
 from pandas.core.reshape.concat import concat
-from pandas.core.shared_docs import _shared_docs
-from pandas.core.sorting import get_indexer_indexer
-from pandas.core.window import (
-    Expanding,
-    ExponentialMovingWindow,
-    Rolling,
-    Window,
+from pandas.core.shared_docs import (
+    _shared_docs,
+    expanding_doc,
+    exponential_moving_window_doc,
+    window_doc,
 )
+from pandas.core.sorting import get_indexer_indexer
 
 from pandas.io.formats.format import (
     DataFrameFormatter,
@@ -203,6 +205,12 @@
     )
     from pandas.core.indexers.objects import BaseIndexer
     from pandas.core.resample import Resampler
+    from pandas.core.window import (
+        Expanding,
+        ExponentialMovingWindow,
+        Rolling,
+        Window,
+    )
 
 # goal is to be able to define the docs close to function, while still being
 # able to share
@@ -11498,7 +11506,7 @@ def prod(
     product = prod
 
     @final
-    @doc(Rolling)
+    @Appender(window_doc)
     def rolling(
         self,
         window: int | dt.timedelta | str | BaseOffset | BaseIndexer,
@@ -11533,6 +11541,11 @@ def rolling(
         else:
             axis = 0
 
+        from pandas.core.window import (
+            Rolling,
+            Window,
+        )
+
         if win_type is not None:
             return Window(
                 self,
@@ -11561,13 +11574,15 @@ def rolling(
         )
 
     @final
-    @doc(Expanding)
+    @Appender(expanding_doc)
     def expanding(
         self,
         min_periods: int = 1,
         axis: Axis | lib.NoDefault = lib.no_default,
         method: str = "single",
     ) -> Expanding:
+        from pandas.core.window import Expanding
+
         if axis is not lib.no_default:
             axis = self._get_axis_number(axis)
             name = "expanding"
@@ -11592,7 +11607,7 @@ def expanding(
         return Expanding(self, min_periods=min_periods, axis=axis, method=method)
 
     @final
-    @doc(ExponentialMovingWindow)
+    @Appender(exponential_moving_window_doc)
     def ewm(
         self,
         com: float | None = None,
@@ -11606,6 +11621,8 @@ def ewm(
         times: np.ndarray | DataFrame | Series | None = None,
         method: str = "single",
     ) -> ExponentialMovingWindow:
+        from pandas.core.window import ExponentialMovingWindow
+
         if axis is not lib.no_default:
             axis = self._get_axis_number(axis)
             name = "ewm"

pandas/core/groupby/ops.py

@@ -673,7 +673,8 @@ def groups(self) -> dict[Hashable, np.ndarray]:
         if len(self.groupings) == 1:
             return self.groupings[0].groups
         else:
-            to_groupby = zip(*(ping.grouping_vector for ping in self.groupings))
+            pings = (ping.grouping_vector for ping in self.groupings)
+            to_groupby = zip(*pings)
             index = Index(to_groupby)
             return self.axis.groupby(index)
 

pandas/core/reshape/pivot.py

@@ -31,7 +31,6 @@
 
 import pandas.core.common as com
 from pandas.core.frame import _shared_docs
-from pandas.core.groupby import Grouper
 from pandas.core.indexes.api import (
     Index,
     MultiIndex,
@@ -143,6 +142,8 @@ def __internal_pivot_table(
             if i not in data:
                 raise KeyError(i)
 
+        from pandas.core.groupby import Grouper
+
         to_filter = []
         for x in keys + values:
             if isinstance(x, Grouper):
@@ -492,6 +493,8 @@ def _all_key():
 
 
 def _convert_by(by):
+    from pandas.core.groupby import Grouper
+
     if by is None:
         by = []
     elif (