From 20511dd76266dd70b7a073da1091a4f52f37a3a4 Mon Sep 17 00:00:00 2001
From: lexual <lex@jbadigital.com>
Date: Sat, 14 Nov 2015 09:26:16 +1100
Subject: [PATCH] PERF: Faster Series construction with no data and
 DatetimeIndex.

ref pydata/pandas#11433

Code. taken from @jreback comment on pydata/pandas#11433
---
 asv_bench/benchmarks/series_methods.py | 14 ++++++++++++++
 doc/source/whatsnew/v0.17.1.txt        |  1 +
 pandas/core/series.py                  | 17 +++++++++++------
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/asv_bench/benchmarks/series_methods.py b/asv_bench/benchmarks/series_methods.py
index a40ed3f1d6482..4e368c6d7cde2 100644
--- a/asv_bench/benchmarks/series_methods.py
+++ b/asv_bench/benchmarks/series_methods.py
@@ -1,6 +1,20 @@
 from .pandas_vb_common import *
 
 
+class series_constructor_no_data_datetime_index(object):
+    goal_time = 0.2
+
+    def setup(self):
+        self.dr = pd.date_range(
+            start=datetime(2015,10,26),
+            end=datetime(2016,1,1),
+            freq='10s'
+        )  # ~500k long
+
+    def time_series_constructor_no_data_datetime_index(self):
+        Series(data=None, index=self.dr)
+
+
 class series_isin_int64(object):
     goal_time = 0.2
 
diff --git a/doc/source/whatsnew/v0.17.1.txt b/doc/source/whatsnew/v0.17.1.txt
index 3d10566e47075..1b8cd270b3e8c 100755
--- a/doc/source/whatsnew/v0.17.1.txt
+++ b/doc/source/whatsnew/v0.17.1.txt
@@ -86,6 +86,7 @@ Performance Improvements
 
 - Improved performance to ``to_excel`` (:issue:`11352`)
 - Performance bug in repr of ``Categorical`` categories, which was rendering the strings before chopping them for display (:issue:`11305`)
+- Improved performance of ``Series`` constructor with no data and ``DatetimeIndex`` (:issue:`11433`)
 
 .. _whatsnew_0171.bug_fixes:
 
diff --git a/pandas/core/series.py b/pandas/core/series.py
index 5106225cdd3c9..bc9a2f466530e 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -171,17 +171,22 @@ def __init__(self, data=None, index=None, dtype=None, name=None,
                         index = Index(_try_sort(data))
                 try:
                     if isinstance(index, DatetimeIndex):
-                        # coerce back to datetime objects for lookup
-                        data = _dict_compat(data)
-                        data = lib.fast_multiget(data, index.astype('O'),
-                                                 default=np.nan)
+                        if len(data):
+                            # coerce back to datetime objects for lookup
+                            data = _dict_compat(data)
+                            data = lib.fast_multiget(data, index.astype('O'),
+                                                     default=np.nan)
+                        else:
+                            data = np.nan
                     elif isinstance(index, PeriodIndex):
-                        data = [data.get(i, nan) for i in index]
+                        data = [data.get(i, nan)
+                                for i in index] if data else np.nan
                     else:
                         data = lib.fast_multiget(data, index.values,
                                                  default=np.nan)
                 except TypeError:
-                    data = [data.get(i, nan) for i in index]
+                    data = [data.get(i, nan)
+                            for i in index] if data else np.nan
 
             elif isinstance(data, SingleBlockManager):
                 if index is None: