From 2dc85a9d521dbc63e681469905ddbee131b0e512 Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Wed, 6 Sep 2017 10:26:53 -0700
Subject: [PATCH 1/2] Use cache_readonly attrs to minimize attrs set in
 __init__

This is a step towards making dateOffset immutable, is an approach suggested by @shoyer
---
 pandas/tseries/offsets.py | 44 +++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/pandas/tseries/offsets.py b/pandas/tseries/offsets.py
index 7ccecaa84e6d6..9267002acbee1 100644
--- a/pandas/tseries/offsets.py
+++ b/pandas/tseries/offsets.py
@@ -11,6 +11,7 @@
 from dateutil.relativedelta import relativedelta, weekday
 from dateutil.easter import easter
 from pandas._libs import tslib, Timestamp, OutOfBoundsDatetime, Timedelta
+from pandas.util._decorators import cache_readonly
 
 import functools
 import operator
@@ -938,12 +939,14 @@ def __init__(self, n=1, normalize=False, **kwds):
         self.normalize = normalize
         super(BusinessHour, self).__init__(**kwds)
 
+    @cache_readonly
+    def next_bday(self):
         # used for moving to next businessday
         if self.n >= 0:
             nb_offset = 1
         else:
             nb_offset = -1
-        self.next_bday = BusinessDay(n=nb_offset)
+        return BusinessDay(n=nb_offset)
 
 
 class CustomBusinessDay(BusinessDay):
@@ -1570,6 +1573,7 @@ class Week(DateOffset):
         Always generate specific day of week. 0 for Monday
     """
     _adjust_dst = True
+    _inc = timedelta(weeks=1)
 
     def __init__(self, n=1, normalize=False, **kwds):
         self.n = n
@@ -1581,7 +1585,6 @@ def __init__(self, n=1, normalize=False, **kwds):
                 raise ValueError('Day must be 0<=day<=6, got {day}'
                                  .format(day=self.weekday))
 
-        self._inc = timedelta(weeks=1)
         self.kwds = kwds
 
     def isAnchored(self):
@@ -1985,13 +1988,6 @@ class QuarterEnd(QuarterOffset):
     _default_startingMonth = 3
     _prefix = 'Q'
 
-    def __init__(self, n=1, normalize=False, **kwds):
-        self.n = n
-        self.normalize = normalize
-        self.startingMonth = kwds.get('startingMonth', 3)
-
-        self.kwds = kwds
-
     def isAnchored(self):
         return (self.n == 1 and self.startingMonth is not None)
 
@@ -2324,12 +2320,28 @@ def __init__(self, n=1, normalize=False, **kwds):
             raise ValueError('{variation} is not a valid variation'
                              .format(variation=self.variation))
 
+    @cache_readonly
+    def _rd_forward(self):
+        if self.variation == "nearest":
+            weekday_offset = weekday(self.weekday)
+            return relativedelta(weekday=weekday_offset)
+        else:
+            return None
+
+    @cache_readonly
+    def _rd_backward(self):
         if self.variation == "nearest":
             weekday_offset = weekday(self.weekday)
-            self._rd_forward = relativedelta(weekday=weekday_offset)
-            self._rd_backward = relativedelta(weekday=weekday_offset(-1))
+            return relativedelta(weekday=weekday_offset(-1))
         else:
-            self._offset_lwom = LastWeekOfMonth(n=1, weekday=self.weekday)
+            return None
+
+    @cache_readonly
+    def _offset_lwom(self):
+        if self.variation == "nearest":
+            return None
+        else:
+            return LastWeekOfMonth(n=1, weekday=self.weekday)
 
     def isAnchored(self):
         return self.n == 1 \
@@ -2550,7 +2562,10 @@ def __init__(self, n=1, normalize=False, **kwds):
         if self.n == 0:
             raise ValueError('N cannot be 0')
 
-        self._offset = FY5253(
+    @cache_readonly
+    def _offset(self):
+        kwds = self.kwds
+        return FY5253(
             startingMonth=kwds['startingMonth'],
             weekday=kwds["weekday"],
             variation=kwds["variation"])
@@ -2660,9 +2675,6 @@ class Easter(DateOffset):
     """
     _adjust_dst = True
 
-    def __init__(self, n=1, **kwds):
-        super(Easter, self).__init__(n, **kwds)
-
     @apply_wraps
     def apply(self, other):
         currentEaster = easter(other.year)

From d2d4e66b190098082bd03d0297e72102f4a70890 Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Wed, 6 Sep 2017 19:52:57 -0700
Subject: [PATCH 2/2] Spell out names per reviewer comments

---
 pandas/tseries/offsets.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pandas/tseries/offsets.py b/pandas/tseries/offsets.py
index 9267002acbee1..36aeff35d3923 100644
--- a/pandas/tseries/offsets.py
+++ b/pandas/tseries/offsets.py
@@ -2321,7 +2321,7 @@ def __init__(self, n=1, normalize=False, **kwds):
                              .format(variation=self.variation))
 
     @cache_readonly
-    def _rd_forward(self):
+    def _relativedelta_forward(self):
         if self.variation == "nearest":
             weekday_offset = weekday(self.weekday)
             return relativedelta(weekday=weekday_offset)
@@ -2329,7 +2329,7 @@ def _rd_forward(self):
             return None
 
     @cache_readonly
-    def _rd_backward(self):
+    def _relativedelta_backward(self):
         if self.variation == "nearest":
             weekday_offset = weekday(self.weekday)
             return relativedelta(weekday=weekday_offset(-1))
@@ -2445,8 +2445,8 @@ def _get_year_end_nearest(self, dt):
         if target_date.weekday() == self.weekday:
             return target_date
         else:
-            forward = target_date + self._rd_forward
-            backward = target_date + self._rd_backward
+            forward = target_date + self._relativedelta_forward
+            backward = target_date + self._relativedelta_backward
 
             if forward - target_date < target_date - backward:
                 return forward