From 52cba23e26b99494e0ed3144028bc937bb1f6ce4 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 29 Jan 2020 16:49:18 +0100
Subject: [PATCH 1/2] PERF: postpone imports in Index constructor

---
 pandas/core/indexes/base.py | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 1738c03e754b2..48eaa41c0735e 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -277,10 +277,6 @@ def __new__(
     ) -> "Index":
 
         from pandas.core.indexes.range import RangeIndex
-        from pandas import PeriodIndex, DatetimeIndex, TimedeltaIndex
-        from pandas.core.indexes.numeric import Float64Index, Int64Index, UInt64Index
-        from pandas.core.indexes.interval import IntervalIndex
-        from pandas.core.indexes.category import CategoricalIndex
 
         name = maybe_extract_name(name, data, cls)
 
@@ -296,10 +292,14 @@ def __new__(
 
         # categorical
         elif is_categorical_dtype(data) or is_categorical_dtype(dtype):
+            from pandas.core.indexes.category import CategoricalIndex
+
             return CategoricalIndex(data, dtype=dtype, copy=copy, name=name, **kwargs)
 
         # interval
         elif is_interval_dtype(data) or is_interval_dtype(dtype):
+            from pandas.core.indexes.interval import IntervalIndex
+
             closed = kwargs.pop("closed", None)
             if is_dtype_equal(_o_dtype, dtype):
                 return IntervalIndex(
@@ -314,6 +314,8 @@ def __new__(
             or is_datetime64_any_dtype(dtype)
             or "tz" in kwargs
         ):
+            from pandas import DatetimeIndex
+
             if is_dtype_equal(_o_dtype, dtype):
                 # GH#23524 passing `dtype=object` to DatetimeIndex is invalid,
                 #  will raise in the where `data` is already tz-aware.  So
@@ -328,6 +330,8 @@ def __new__(
                 return DatetimeIndex(data, copy=copy, name=name, dtype=dtype, **kwargs)
 
         elif is_timedelta64_dtype(data) or is_timedelta64_dtype(dtype):
+            from pandas import TimedeltaIndex
+
             if is_dtype_equal(_o_dtype, dtype):
                 # Note we can pass copy=False because the .astype below
                 #  will always make a copy
@@ -338,6 +342,8 @@ def __new__(
                 return TimedeltaIndex(data, copy=copy, name=name, dtype=dtype, **kwargs)
 
         elif is_period_dtype(data) or is_period_dtype(dtype):
+            from pandas import PeriodIndex
+
             if is_dtype_equal(_o_dtype, dtype):
                 return PeriodIndex(data, copy=False, name=name, **kwargs).astype(object)
             return PeriodIndex(data, dtype=dtype, copy=copy, name=name, **kwargs)
@@ -357,6 +363,12 @@ def __new__(
 
         # index-like
         elif isinstance(data, (np.ndarray, Index, ABCSeries)):
+            from pandas.core.indexes.numeric import (
+                Float64Index,
+                Int64Index,
+                UInt64Index,
+            )
+
             if dtype is not None:
                 # we need to avoid having numpy coerce
                 # things that look like ints/floats to ints unless

From dd6ee1b47231f476c5cdd3a9e54f9e733b160653 Mon Sep 17 00:00:00 2001
From: Tom Augspurger <tom.w.augspurger@gmail.com>
Date: Wed, 29 Jan 2020 10:57:01 -0600
Subject: [PATCH 2/2] added comments

---
 pandas/core/indexes/base.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 48eaa41c0735e..5274213f114e3 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -292,12 +292,14 @@ def __new__(
 
         # categorical
         elif is_categorical_dtype(data) or is_categorical_dtype(dtype):
+            # Delay import for perf. https://github.com/pandas-dev/pandas/pull/31423
             from pandas.core.indexes.category import CategoricalIndex
 
             return CategoricalIndex(data, dtype=dtype, copy=copy, name=name, **kwargs)
 
         # interval
         elif is_interval_dtype(data) or is_interval_dtype(dtype):
+            # Delay import for perf. https://github.com/pandas-dev/pandas/pull/31423
             from pandas.core.indexes.interval import IntervalIndex
 
             closed = kwargs.pop("closed", None)
@@ -314,6 +316,7 @@ def __new__(
             or is_datetime64_any_dtype(dtype)
             or "tz" in kwargs
         ):
+            # Delay import for perf. https://github.com/pandas-dev/pandas/pull/31423
             from pandas import DatetimeIndex
 
             if is_dtype_equal(_o_dtype, dtype):
@@ -330,6 +333,7 @@ def __new__(
                 return DatetimeIndex(data, copy=copy, name=name, dtype=dtype, **kwargs)
 
         elif is_timedelta64_dtype(data) or is_timedelta64_dtype(dtype):
+            # Delay import for perf. https://github.com/pandas-dev/pandas/pull/31423
             from pandas import TimedeltaIndex
 
             if is_dtype_equal(_o_dtype, dtype):
@@ -342,6 +346,7 @@ def __new__(
                 return TimedeltaIndex(data, copy=copy, name=name, dtype=dtype, **kwargs)
 
         elif is_period_dtype(data) or is_period_dtype(dtype):
+            # Delay import for perf. https://github.com/pandas-dev/pandas/pull/31423
             from pandas import PeriodIndex
 
             if is_dtype_equal(_o_dtype, dtype):
@@ -363,6 +368,7 @@ def __new__(
 
         # index-like
         elif isinstance(data, (np.ndarray, Index, ABCSeries)):
+            # Delay import for perf. https://github.com/pandas-dev/pandas/pull/31423
             from pandas.core.indexes.numeric import (
                 Float64Index,
                 Int64Index,