From 451d27d75797d052e1186a8201dc589da122cca2 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Wed, 26 Aug 2020 19:57:40 -0600
Subject: [PATCH 01/16] fix for issue #198

---
 cftime/__init__.py  |   1 +
 cftime/_cftime.pyx  | 100 +++++++++++++++++++++++++-------------------
 test/test_cftime.py |   4 +-
 3 files changed, 59 insertions(+), 46 deletions(-)

diff --git a/cftime/__init__.py b/cftime/__init__.py
index 7138316d..415214a0 100644
--- a/cftime/__init__.py
+++ b/cftime/__init__.py
@@ -6,4 +6,5 @@
 from ._cftime import microsec_units, millisec_units, \
                          sec_units, hr_units, day_units, min_units
 from ._cftime import num2date, date2num, date2index, num2pydate
+from ._cftime import to_calendar_specific_datetime
 from ._cftime import __version__
diff --git a/cftime/_cftime.pyx b/cftime/_cftime.pyx
index 0caa6641..f2f96220 100644
--- a/cftime/_cftime.pyx
+++ b/cftime/_cftime.pyx
@@ -148,8 +148,8 @@ def _dateparse(timestr,calendar):
             pass
     if not basedate:
         if not utc_offset:
-            basedate = datetime(year, month, day, hour, minute, second,
-                    microsecond)
+            basedate = _datetime(year, month, day, hour, minute, second,
+                                 microsecond)
         else:
             raise ValueError('cannot use utc_offset for this reference date/calendar')
     if calendar in ['julian', 'standard', 'gregorian', 'proleptic_gregorian']:
@@ -246,7 +246,7 @@ def date2num(dates,units,calendar='standard'):
             # remove time zone offset
             if getattr(date, 'tzinfo',None) is not None:
                 date = date.replace(tzinfo=None) - date.utcoffset()
-        else: # convert date to same calendar specific cftime.datetime instance
+        else: # convert date to same calendar specific cftime._datetime instance
             if not isinstance(date, DATE_TYPES[calendar]):
                 date = to_calendar_specific_datetime(date, calendar, False)
         if ismasked and mask.flat[n]:
@@ -332,20 +332,20 @@ DATE_TYPES = {
 }
 
 
-def to_calendar_specific_datetime(datetime, calendar, use_python_datetime):
+def to_calendar_specific_datetime(dt, calendar, use_python_datetime):
     if use_python_datetime:
         date_type = real_datetime
     else:
         date_type = DATE_TYPES[calendar]
 
     return date_type(
-        datetime.year,
-        datetime.month,
-        datetime.day,
-        datetime.hour,
-        datetime.minute,
-        datetime.second,
-        datetime.microsecond
+        dt.year,
+        dt.month,
+        dt.day,
+        dt.hour,
+        dt.minute,
+        dt.second,
+        dt.microsecond
     )
 
 
@@ -435,7 +435,7 @@ def num2date(
 
     **only_use_cftime_datetimes**: if False, python datetime.datetime
     objects are returned from num2date where possible; if True dates which
-    subclass cftime.datetime are returned for all calendars. Default **True**.
+    subclass cftime._datetime are returned for all calendars. Default **True**.
 
     **only_use_python_datetimes**: always return python datetime.datetime
     objects and raise an error if this is not possible. Ignored unless
@@ -498,7 +498,7 @@ def num2date(
 
     # Through np.timedelta64, convert integers scaled to have units of
     # microseconds to datetime.timedelta objects, the timedelta type compatible
-    # with all cftime.datetime objects.
+    # with all cftime._datetime objects.
     deltas = scaled_times.astype("timedelta64[us]").astype(timedelta)
     try:
         return basedate + deltas
@@ -841,7 +841,19 @@ cdef to_tuple(dt):
             dt.second, dt.microsecond)
 
 @cython.embedsignature(True)
-cdef class datetime(object):
+def datetime(year, month, day, hour=0, minute=0,
+             second=0, microsecond=0, dayofwk=-1, 
+             dayofyr = -1, calendar='standard'):
+    """
+Create a calendar specific datetime instance.
+    """
+    if calendar == '':
+        return _datetime(year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr,calendar=calendar)
+    else:
+        date_type = DATE_TYPES[calendar]
+        return date_type(year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr)
+
+cdef class _datetime(object):
     """
 The base class implementing most methods of datetime classes that
 mimic datetime.datetime but support calendars other than the proleptic
@@ -854,7 +866,7 @@ Gregorial calendar.
 
     # Python's datetime.datetime uses the proleptic Gregorian
     # calendar. This boolean is used to decide whether a
-    # cftime.datetime instance can be converted to
+    # cftime._datetime instance can be converted to
     # datetime.datetime.
     cdef readonly bint datetime_compatible
 
@@ -997,9 +1009,9 @@ Gregorial calendar.
                 self.second, self.microsecond)
 
     def __richcmp__(self, other, int op):
-        cdef datetime dt, dt_other
+        cdef _datetime dt, dt_other
         dt = self
-        if isinstance(other, datetime):
+        if isinstance(other, _datetime):
             dt_other = other
             # comparing two datetime instances
             if dt.calendar == dt_other.calendar:
@@ -1054,11 +1066,11 @@ Gregorial calendar.
         return NotImplemented
 
     def __add__(self, other):
-        cdef datetime dt
-        if isinstance(self, datetime) and isinstance(other, timedelta):
+        cdef _datetime dt
+        if isinstance(self, _datetime) and isinstance(other, timedelta):
             dt = self
             delta = other
-        elif isinstance(self, timedelta) and isinstance(other, datetime):
+        elif isinstance(self, timedelta) and isinstance(other, _datetime):
             dt = other
             delta = self
         else:
@@ -1066,10 +1078,10 @@ Gregorial calendar.
         return dt._add_timedelta(delta)
 
     def __sub__(self, other):
-        cdef datetime dt
-        if isinstance(self, datetime): # left arg is a datetime instance
+        cdef _datetime dt
+        if isinstance(self, _datetime): # left arg is a datetime instance
             dt = self
-            if isinstance(other, datetime):
+            if isinstance(other, _datetime):
                 # datetime - datetime
                 if dt.calendar != other.calendar:
                     raise ValueError("cannot compute the time difference between dates with different calendars")
@@ -1113,13 +1125,13 @@ datetime object."""
                 return NotImplemented
 
 @cython.embedsignature(True)
-cdef class DatetimeNoLeap(datetime):
+cdef class DatetimeNoLeap(_datetime):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "noleap" ("365_day") calendar.
     """
     def __init__(self, *args, **kwargs):
-        datetime.__init__(self, *args, **kwargs)
+        _datetime.__init__(self, *args, **kwargs)
         self.calendar = "noleap"
         self.datetime_compatible = False
         assert_valid_date(self, no_leap, False, has_year_zero=True)
@@ -1132,13 +1144,13 @@ but uses the "noleap" ("365_day") calendar.
         return _dpm[self.month-1]
 
 @cython.embedsignature(True)
-cdef class DatetimeAllLeap(datetime):
+cdef class DatetimeAllLeap(_datetime):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "all_leap" ("366_day") calendar.
     """
     def __init__(self, *args, **kwargs):
-        datetime.__init__(self, *args, **kwargs)
+        _datetime.__init__(self, *args, **kwargs)
         self.calendar = "all_leap"
         self.datetime_compatible = False
         assert_valid_date(self, all_leap, False, has_year_zero=True)
@@ -1151,13 +1163,13 @@ but uses the "all_leap" ("366_day") calendar.
         return _dpm_leap[self.month-1]
 
 @cython.embedsignature(True)
-cdef class Datetime360Day(datetime):
+cdef class Datetime360Day(_datetime):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "360_day" calendar.
     """
     def __init__(self, *args, **kwargs):
-        datetime.__init__(self, *args, **kwargs)
+        _datetime.__init__(self, *args, **kwargs)
         self.calendar = "360_day"
         self.datetime_compatible = False
         assert_valid_date(self, no_leap, False, has_year_zero=True, is_360_day=True)
@@ -1170,13 +1182,13 @@ but uses the "360_day" calendar.
         return _dpm_360[self.month-1]
 
 @cython.embedsignature(True)
-cdef class DatetimeJulian(datetime):
+cdef class DatetimeJulian(_datetime):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "julian" calendar.
     """
     def __init__(self, *args, **kwargs):
-        datetime.__init__(self, *args, **kwargs)
+        _datetime.__init__(self, *args, **kwargs)
         self.calendar = "julian"
         self.datetime_compatible = False
         assert_valid_date(self, is_leap_julian, False)
@@ -1185,7 +1197,7 @@ but uses the "julian" calendar.
         return DatetimeJulian(*add_timedelta(self, delta, is_leap_julian, False, False))
 
 @cython.embedsignature(True)
-cdef class DatetimeGregorian(datetime):
+cdef class DatetimeGregorian(_datetime):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the mixed Julian-Gregorian ("standard", "gregorian") calendar.
@@ -1199,7 +1211,7 @@ datetime.datetime instances and used to compute time differences
 a datetime.datetime instance or vice versa.
     """
     def __init__(self, *args, **kwargs):
-        datetime.__init__(self, *args, **kwargs)
+        _datetime.__init__(self, *args, **kwargs)
         self.calendar = "gregorian"
 
         # dates after 1582-10-15 can be converted to and compared to
@@ -1214,7 +1226,7 @@ a datetime.datetime instance or vice versa.
         return DatetimeGregorian(*add_timedelta(self, delta, is_leap_gregorian, True, False))
 
 @cython.embedsignature(True)
-cdef class DatetimeProlepticGregorian(datetime):
+cdef class DatetimeProlepticGregorian(_datetime):
     """
 Phony datetime object which mimics the python datetime object,
 but allows for dates that don't exist in the proleptic gregorian calendar.
@@ -1225,14 +1237,14 @@ Has strftime, timetuple, replace, __repr__, and __str__ methods. The
 format of the string produced by __str__ is controlled by self.format
 (default %Y-%m-%d %H:%M:%S). Supports comparisons with other
 datetime instances using the same calendar; comparison with
-native python datetime instances is possible for cftime.datetime
+native python datetime instances is possible for cftime._datetime
 instances using 'gregorian' and 'proleptic_gregorian' calendars.
 
 Instance variables are year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr,
 format, and calendar.
     """
     def __init__(self, *args, **kwargs):
-        datetime.__init__(self, *args, **kwargs)
+        _datetime.__init__(self, *args, **kwargs)
         self.calendar = "proleptic_gregorian"
         self.datetime_compatible = True
         assert_valid_date(self, is_leap_proleptic_gregorian, False)
@@ -1261,7 +1273,7 @@ cdef _findall(text, substr):
 # calendar.  ;)
 
 
-cdef _strftime(datetime dt, fmt):
+cdef _strftime(_datetime dt, fmt):
     if _illegal_s.search(fmt):
         raise TypeError("This strftime implementation does not handle %s")
     # don't use strftime method at all.
@@ -1321,7 +1333,7 @@ cdef int * month_lengths(bint (*is_leap)(int), int year):
     else:
         return _dpm
 
-cdef void assert_valid_date(datetime dt, bint (*is_leap)(int),
+cdef void assert_valid_date(_datetime dt, bint (*is_leap)(int),
                             bint julian_gregorian_mixed,
                             bint has_year_zero=False,
                             bint is_360_day=False) except *:
@@ -1356,7 +1368,7 @@ cdef void assert_valid_date(datetime dt, bint (*is_leap)(int),
     if dt.microsecond < 0 or dt.microsecond > 999999:
         raise ValueError("invalid microsecond provided in {0!r}".format(dt))
 
-# Add a datetime.timedelta to a cftime.datetime instance. Uses
+# Add a datetime.timedelta to a cftime._datetime instance. Uses
 # integer arithmetic to avoid rounding errors and preserve
 # microsecond accuracy.
 #
@@ -1370,7 +1382,7 @@ cdef void assert_valid_date(datetime dt, bint (*is_leap)(int),
 # The date of the transition from the Julian to Gregorian calendar and
 # the number of invalid dates are hard-wired (1582-10-4 is the last day
 # of the Julian calendar, after which follows 1582-10-15).
-cdef tuple add_timedelta(datetime dt, delta, bint (*is_leap)(int), bint julian_gregorian_mixed, bint has_year_zero):
+cdef tuple add_timedelta(_datetime dt, delta, bint (*is_leap)(int), bint julian_gregorian_mixed, bint has_year_zero):
     cdef int microsecond, second, minute, hour, day, month, year
     cdef int delta_microseconds, delta_seconds, delta_days
     cdef int* month_length
@@ -1444,13 +1456,13 @@ cdef tuple add_timedelta(datetime dt, delta, bint (*is_leap)(int), bint julian_g
 
     return (year, month, day, hour, minute, second, microsecond, -1, -1)
 
-# Add a datetime.timedelta to a cftime.datetime instance with the 360_day calendar.
+# Add a datetime.timedelta to a cftime._datetime instance with the 360_day calendar.
 #
 # Assumes that the 360_day,365_day and 366_day calendars (unlike the rest of supported
 # calendars) have the year 0. Also, there are no leap years and all
 # months are 30 days long, so we can compute month and year by using
 # "//" and "%".
-cdef tuple add_timedelta_360_day(datetime dt, delta):
+cdef tuple add_timedelta_360_day(_datetime dt, delta):
     cdef int microsecond, second, minute, hour, day, month, year
     cdef int delta_microseconds, delta_seconds, delta_days
 
@@ -1870,7 +1882,7 @@ def DateFromJulianDay(JD, calendar='standard', only_use_cftime_datetimes=True,
 
     if calendar='julian', Julian Day follows julian calendar.
 
-    If only_use_cftime_datetimes is set to True, then cftime.datetime
+    If only_use_cftime_datetimes is set to True, then cftime._datetime
     objects are returned for all calendars.  Otherwise the datetime object is a
     native python datetime object if the date falls in the Gregorian calendar
     (i.e. calendar='proleptic_gregorian', or  calendar = 'standard'/'gregorian'
@@ -2121,7 +2133,7 @@ are:
 
 @keyword only_use_cftime_datetimes: if False, datetime.datetime
 objects are returned from num2date where possible; if True dates which subclass
-cftime.datetime are returned for all calendars. Default True.
+cftime._datetime are returned for all calendars. Default True.
 
 @keyword only_use_python_datetimes: always return python datetime.datetime
 objects and raise an error if this is not possible. Ignored unless
diff --git a/test/test_cftime.py b/test/test_cftime.py
index 3e68b5ee..87a1792e 100644
--- a/test/test_cftime.py
+++ b/test/test_cftime.py
@@ -248,7 +248,7 @@ def test_tz_naive(self):
         # check date2num,num2date methods.
         # use datetime from cftime, since this date doesn't
         # exist in "normal" calendars.
-        d = datetimex(2000, 2, 30)
+        d = datetimex(2000, 2, 30, calendar='360_day')
         t1 = self.cdftime_360day.date2num(d)
         assert_almost_equal(t1, 360 * 400.)
         d2 = self.cdftime_360day.num2date(t1)
@@ -1581,7 +1581,7 @@ def test_num2date_only_use_cftime_datetimes_post_gregorian(
 
 def test_repr():
     #expected = 'cftime.datetime(2000-01-01 00:00:00)'
-    expected = 'cftime.datetime(2000, 1, 1, 0, 0, 0, 0)'
+    expected = 'cftime.DatetimeGregorian(2000, 1, 1, 0, 0, 0, 0)'
     assert repr(datetimex(2000, 1, 1)) == expected
 
 

From 4c577453bb7d89771711ebb26fb2f5bf940b3195 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Wed, 26 Aug 2020 20:00:31 -0600
Subject: [PATCH 02/16] update

---
 cftime/__init__.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/cftime/__init__.py b/cftime/__init__.py
index 415214a0..7138316d 100644
--- a/cftime/__init__.py
+++ b/cftime/__init__.py
@@ -6,5 +6,4 @@
 from ._cftime import microsec_units, millisec_units, \
                          sec_units, hr_units, day_units, min_units
 from ._cftime import num2date, date2num, date2index, num2pydate
-from ._cftime import to_calendar_specific_datetime
 from ._cftime import __version__

From 574430bca7df9c2f7c02875487953f9e48003514 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Wed, 26 Aug 2020 20:03:35 -0600
Subject: [PATCH 03/16] bump version number

---
 Changelog          | 6 ++++--
 cftime/_cftime.pyx | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Changelog b/Changelog
index 78ae9c1d..e5b500fb 100644
--- a/Changelog
+++ b/Changelog
@@ -1,6 +1,8 @@
-since version 1.2.1
-===================
+version 1.2.2 (not yet released)
+================================
  * zero pad years in strtime (issue #194)
+ * have cftime.datetime create calendar-specific instances that support
+   addition and subtraction (issue #198.)
 
 version 1.2.1 (release tag v1.2.1rel)
 =====================================
diff --git a/cftime/_cftime.pyx b/cftime/_cftime.pyx
index f2f96220..64b4a909 100644
--- a/cftime/_cftime.pyx
+++ b/cftime/_cftime.pyx
@@ -53,7 +53,7 @@ cdef int32_t* days_per_month_array = [
 _rop_lookup = {Py_LT: '__gt__', Py_LE: '__ge__', Py_EQ: '__eq__',
                Py_GT: '__lt__', Py_GE: '__le__', Py_NE: '__ne__'}
 
-__version__ = '1.2.1'
+__version__ = '1.2.2'
 
 # Adapted from http://delete.me.uk/2005/03/iso8601.html
 # Note: This regex ensures that all ISO8601 timezone formats are accepted - but, due to legacy support for other timestrings, not all incorrect formats can be rejected.

From aa9895bfb90423a0be85a9435fa55e55fb71d443 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Wed, 26 Aug 2020 20:04:04 -0600
Subject: [PATCH 04/16] update

---
 Changelog | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Changelog b/Changelog
index e5b500fb..9b9fbd0b 100644
--- a/Changelog
+++ b/Changelog
@@ -2,7 +2,7 @@ version 1.2.2 (not yet released)
 ================================
  * zero pad years in strtime (issue #194)
  * have cftime.datetime create calendar-specific instances that support
-   addition and subtraction (issue #198.)
+   addition and subtraction (issue #198).
 
 version 1.2.1 (release tag v1.2.1rel)
 =====================================

From 741f22a517da5c3614d0fe9d647c2427616ef649 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Fri, 28 Aug 2020 21:23:16 -0600
Subject: [PATCH 05/16] expose base class, renamed to datetime_base

---
 cftime/__init__.py |  2 +-
 cftime/_cftime.pyx | 72 +++++++++++++++++++++++-----------------------
 2 files changed, 37 insertions(+), 37 deletions(-)

diff --git a/cftime/__init__.py b/cftime/__init__.py
index 7138316d..b185a0be 100644
--- a/cftime/__init__.py
+++ b/cftime/__init__.py
@@ -1,6 +1,6 @@
 from ._cftime import utime, JulianDayFromDate, DateFromJulianDay, UNIT_CONVERSION_FACTORS
 from ._cftime import _parse_date, date2index, time2index
-from ._cftime import datetime, real_datetime
+from ._cftime import datetime, real_datetime, datetime_base
 from ._cftime import DatetimeNoLeap, DatetimeAllLeap, Datetime360Day, DatetimeJulian, \
                          DatetimeGregorian, DatetimeProlepticGregorian
 from ._cftime import microsec_units, millisec_units, \
diff --git a/cftime/_cftime.pyx b/cftime/_cftime.pyx
index 64b4a909..ccb16da6 100644
--- a/cftime/_cftime.pyx
+++ b/cftime/_cftime.pyx
@@ -148,7 +148,7 @@ def _dateparse(timestr,calendar):
             pass
     if not basedate:
         if not utc_offset:
-            basedate = _datetime(year, month, day, hour, minute, second,
+            basedate = datetime_base(year, month, day, hour, minute, second,
                                  microsecond)
         else:
             raise ValueError('cannot use utc_offset for this reference date/calendar')
@@ -246,7 +246,7 @@ def date2num(dates,units,calendar='standard'):
             # remove time zone offset
             if getattr(date, 'tzinfo',None) is not None:
                 date = date.replace(tzinfo=None) - date.utcoffset()
-        else: # convert date to same calendar specific cftime._datetime instance
+        else: # convert date to same calendar specific cftime.datetime_base instance
             if not isinstance(date, DATE_TYPES[calendar]):
                 date = to_calendar_specific_datetime(date, calendar, False)
         if ismasked and mask.flat[n]:
@@ -435,7 +435,7 @@ def num2date(
 
     **only_use_cftime_datetimes**: if False, python datetime.datetime
     objects are returned from num2date where possible; if True dates which
-    subclass cftime._datetime are returned for all calendars. Default **True**.
+    subclass cftime.datetime_base are returned for all calendars. Default **True**.
 
     **only_use_python_datetimes**: always return python datetime.datetime
     objects and raise an error if this is not possible. Ignored unless
@@ -498,7 +498,7 @@ def num2date(
 
     # Through np.timedelta64, convert integers scaled to have units of
     # microseconds to datetime.timedelta objects, the timedelta type compatible
-    # with all cftime._datetime objects.
+    # with all cftime.datetime_base objects.
     deltas = scaled_times.astype("timedelta64[us]").astype(timedelta)
     try:
         return basedate + deltas
@@ -848,12 +848,12 @@ def datetime(year, month, day, hour=0, minute=0,
 Create a calendar specific datetime instance.
     """
     if calendar == '':
-        return _datetime(year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr,calendar=calendar)
+        return datetime_base(year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr,calendar=calendar)
     else:
         date_type = DATE_TYPES[calendar]
         return date_type(year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr)
 
-cdef class _datetime(object):
+cdef class datetime_base(object):
     """
 The base class implementing most methods of datetime classes that
 mimic datetime.datetime but support calendars other than the proleptic
@@ -866,7 +866,7 @@ Gregorial calendar.
 
     # Python's datetime.datetime uses the proleptic Gregorian
     # calendar. This boolean is used to decide whether a
-    # cftime._datetime instance can be converted to
+    # cftime.datetime_base instance can be converted to
     # datetime.datetime.
     cdef readonly bint datetime_compatible
 
@@ -1009,9 +1009,9 @@ Gregorial calendar.
                 self.second, self.microsecond)
 
     def __richcmp__(self, other, int op):
-        cdef _datetime dt, dt_other
+        cdef datetime_base dt, dt_other
         dt = self
-        if isinstance(other, _datetime):
+        if isinstance(other, datetime_base):
             dt_other = other
             # comparing two datetime instances
             if dt.calendar == dt_other.calendar:
@@ -1066,11 +1066,11 @@ Gregorial calendar.
         return NotImplemented
 
     def __add__(self, other):
-        cdef _datetime dt
-        if isinstance(self, _datetime) and isinstance(other, timedelta):
+        cdef datetime_base dt
+        if isinstance(self, datetime_base) and isinstance(other, timedelta):
             dt = self
             delta = other
-        elif isinstance(self, timedelta) and isinstance(other, _datetime):
+        elif isinstance(self, timedelta) and isinstance(other, datetime_base):
             dt = other
             delta = self
         else:
@@ -1078,10 +1078,10 @@ Gregorial calendar.
         return dt._add_timedelta(delta)
 
     def __sub__(self, other):
-        cdef _datetime dt
-        if isinstance(self, _datetime): # left arg is a datetime instance
+        cdef datetime_base dt
+        if isinstance(self, datetime_base): # left arg is a datetime instance
             dt = self
-            if isinstance(other, _datetime):
+            if isinstance(other, datetime_base):
                 # datetime - datetime
                 if dt.calendar != other.calendar:
                     raise ValueError("cannot compute the time difference between dates with different calendars")
@@ -1125,13 +1125,13 @@ datetime object."""
                 return NotImplemented
 
 @cython.embedsignature(True)
-cdef class DatetimeNoLeap(_datetime):
+cdef class DatetimeNoLeap(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "noleap" ("365_day") calendar.
     """
     def __init__(self, *args, **kwargs):
-        _datetime.__init__(self, *args, **kwargs)
+        datetime_base.__init__(self, *args, **kwargs)
         self.calendar = "noleap"
         self.datetime_compatible = False
         assert_valid_date(self, no_leap, False, has_year_zero=True)
@@ -1144,13 +1144,13 @@ but uses the "noleap" ("365_day") calendar.
         return _dpm[self.month-1]
 
 @cython.embedsignature(True)
-cdef class DatetimeAllLeap(_datetime):
+cdef class DatetimeAllLeap(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "all_leap" ("366_day") calendar.
     """
     def __init__(self, *args, **kwargs):
-        _datetime.__init__(self, *args, **kwargs)
+        datetime_base.__init__(self, *args, **kwargs)
         self.calendar = "all_leap"
         self.datetime_compatible = False
         assert_valid_date(self, all_leap, False, has_year_zero=True)
@@ -1163,13 +1163,13 @@ but uses the "all_leap" ("366_day") calendar.
         return _dpm_leap[self.month-1]
 
 @cython.embedsignature(True)
-cdef class Datetime360Day(_datetime):
+cdef class Datetime360Day(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "360_day" calendar.
     """
     def __init__(self, *args, **kwargs):
-        _datetime.__init__(self, *args, **kwargs)
+        datetime_base.__init__(self, *args, **kwargs)
         self.calendar = "360_day"
         self.datetime_compatible = False
         assert_valid_date(self, no_leap, False, has_year_zero=True, is_360_day=True)
@@ -1182,13 +1182,13 @@ but uses the "360_day" calendar.
         return _dpm_360[self.month-1]
 
 @cython.embedsignature(True)
-cdef class DatetimeJulian(_datetime):
+cdef class DatetimeJulian(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "julian" calendar.
     """
     def __init__(self, *args, **kwargs):
-        _datetime.__init__(self, *args, **kwargs)
+        datetime_base.__init__(self, *args, **kwargs)
         self.calendar = "julian"
         self.datetime_compatible = False
         assert_valid_date(self, is_leap_julian, False)
@@ -1197,7 +1197,7 @@ but uses the "julian" calendar.
         return DatetimeJulian(*add_timedelta(self, delta, is_leap_julian, False, False))
 
 @cython.embedsignature(True)
-cdef class DatetimeGregorian(_datetime):
+cdef class DatetimeGregorian(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the mixed Julian-Gregorian ("standard", "gregorian") calendar.
@@ -1211,7 +1211,7 @@ datetime.datetime instances and used to compute time differences
 a datetime.datetime instance or vice versa.
     """
     def __init__(self, *args, **kwargs):
-        _datetime.__init__(self, *args, **kwargs)
+        datetime_base.__init__(self, *args, **kwargs)
         self.calendar = "gregorian"
 
         # dates after 1582-10-15 can be converted to and compared to
@@ -1226,7 +1226,7 @@ a datetime.datetime instance or vice versa.
         return DatetimeGregorian(*add_timedelta(self, delta, is_leap_gregorian, True, False))
 
 @cython.embedsignature(True)
-cdef class DatetimeProlepticGregorian(_datetime):
+cdef class DatetimeProlepticGregorian(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but allows for dates that don't exist in the proleptic gregorian calendar.
@@ -1237,14 +1237,14 @@ Has strftime, timetuple, replace, __repr__, and __str__ methods. The
 format of the string produced by __str__ is controlled by self.format
 (default %Y-%m-%d %H:%M:%S). Supports comparisons with other
 datetime instances using the same calendar; comparison with
-native python datetime instances is possible for cftime._datetime
+native python datetime instances is possible for cftime.datetime_base
 instances using 'gregorian' and 'proleptic_gregorian' calendars.
 
 Instance variables are year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr,
 format, and calendar.
     """
     def __init__(self, *args, **kwargs):
-        _datetime.__init__(self, *args, **kwargs)
+        datetime_base.__init__(self, *args, **kwargs)
         self.calendar = "proleptic_gregorian"
         self.datetime_compatible = True
         assert_valid_date(self, is_leap_proleptic_gregorian, False)
@@ -1273,7 +1273,7 @@ cdef _findall(text, substr):
 # calendar.  ;)
 
 
-cdef _strftime(_datetime dt, fmt):
+cdef _strftime(datetime_base dt, fmt):
     if _illegal_s.search(fmt):
         raise TypeError("This strftime implementation does not handle %s")
     # don't use strftime method at all.
@@ -1333,7 +1333,7 @@ cdef int * month_lengths(bint (*is_leap)(int), int year):
     else:
         return _dpm
 
-cdef void assert_valid_date(_datetime dt, bint (*is_leap)(int),
+cdef void assert_valid_date(datetime_base dt, bint (*is_leap)(int),
                             bint julian_gregorian_mixed,
                             bint has_year_zero=False,
                             bint is_360_day=False) except *:
@@ -1368,7 +1368,7 @@ cdef void assert_valid_date(_datetime dt, bint (*is_leap)(int),
     if dt.microsecond < 0 or dt.microsecond > 999999:
         raise ValueError("invalid microsecond provided in {0!r}".format(dt))
 
-# Add a datetime.timedelta to a cftime._datetime instance. Uses
+# Add a datetime.timedelta to a cftime.datetime_base instance. Uses
 # integer arithmetic to avoid rounding errors and preserve
 # microsecond accuracy.
 #
@@ -1382,7 +1382,7 @@ cdef void assert_valid_date(_datetime dt, bint (*is_leap)(int),
 # The date of the transition from the Julian to Gregorian calendar and
 # the number of invalid dates are hard-wired (1582-10-4 is the last day
 # of the Julian calendar, after which follows 1582-10-15).
-cdef tuple add_timedelta(_datetime dt, delta, bint (*is_leap)(int), bint julian_gregorian_mixed, bint has_year_zero):
+cdef tuple add_timedelta(datetime_base dt, delta, bint (*is_leap)(int), bint julian_gregorian_mixed, bint has_year_zero):
     cdef int microsecond, second, minute, hour, day, month, year
     cdef int delta_microseconds, delta_seconds, delta_days
     cdef int* month_length
@@ -1456,13 +1456,13 @@ cdef tuple add_timedelta(_datetime dt, delta, bint (*is_leap)(int), bint julian_
 
     return (year, month, day, hour, minute, second, microsecond, -1, -1)
 
-# Add a datetime.timedelta to a cftime._datetime instance with the 360_day calendar.
+# Add a datetime.timedelta to a cftime.datetime_base instance with the 360_day calendar.
 #
 # Assumes that the 360_day,365_day and 366_day calendars (unlike the rest of supported
 # calendars) have the year 0. Also, there are no leap years and all
 # months are 30 days long, so we can compute month and year by using
 # "//" and "%".
-cdef tuple add_timedelta_360_day(_datetime dt, delta):
+cdef tuple add_timedelta_360_day(datetime_base dt, delta):
     cdef int microsecond, second, minute, hour, day, month, year
     cdef int delta_microseconds, delta_seconds, delta_days
 
@@ -1882,7 +1882,7 @@ def DateFromJulianDay(JD, calendar='standard', only_use_cftime_datetimes=True,
 
     if calendar='julian', Julian Day follows julian calendar.
 
-    If only_use_cftime_datetimes is set to True, then cftime._datetime
+    If only_use_cftime_datetimes is set to True, then cftime.datetime_base
     objects are returned for all calendars.  Otherwise the datetime object is a
     native python datetime object if the date falls in the Gregorian calendar
     (i.e. calendar='proleptic_gregorian', or  calendar = 'standard'/'gregorian'
@@ -2133,7 +2133,7 @@ are:
 
 @keyword only_use_cftime_datetimes: if False, datetime.datetime
 objects are returned from num2date where possible; if True dates which subclass
-cftime._datetime are returned for all calendars. Default True.
+cftime.datetime_base are returned for all calendars. Default True.
 
 @keyword only_use_python_datetimes: always return python datetime.datetime
 objects and raise an error if this is not possible. Ignored unless

From 67af9f03cb79ab4229276c9332152c1099926bd7 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Fri, 28 Aug 2020 21:26:25 -0600
Subject: [PATCH 06/16] update docstring

---
 cftime/_cftime.pyx | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/cftime/_cftime.pyx b/cftime/_cftime.pyx
index ccb16da6..1b98b6fe 100644
--- a/cftime/_cftime.pyx
+++ b/cftime/_cftime.pyx
@@ -857,7 +857,8 @@ cdef class datetime_base(object):
     """
 The base class implementing most methods of datetime classes that
 mimic datetime.datetime but support calendars other than the proleptic
-Gregorial calendar.
+Gregorial calendar. The factory function cftime.datetime should be used
+to create calendar-specific sub-class instances.
     """
     cdef readonly int year, month, day, hour, minute
     cdef readonly int second, microsecond

From 39fe1a18c2c7a5202f92d623559521f6fbf1857b Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 29 Aug 2020 13:45:20 -0600
Subject: [PATCH 07/16] update

---
 Changelog | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Changelog b/Changelog
index 9b9fbd0b..16d838e3 100644
--- a/Changelog
+++ b/Changelog
@@ -1,8 +1,11 @@
 version 1.2.2 (not yet released)
 ================================
  * zero pad years in strtime (issue #194)
- * have cftime.datetime create calendar-specific instances that support
-   addition and subtraction (issue #198).
+ * have `cftime.datetime` create calendar-specific instances that support
+   addition and subtraction (issue #198). Name of base class changed
+   from `cftime.datetime` to `cftime.datetime_base` (if your are using 
+   `isinstance(my_datetime, cftime.datetime)` this will need to be changed
+   to `isinstance(my_datetime, cftime.datetime_base)`.
 
 version 1.2.1 (release tag v1.2.1rel)
 =====================================

From 3d1c2d96287496856f1104268f1994cea0f20017 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 29 Aug 2020 16:51:49 -0600
Subject: [PATCH 08/16] add test for issue #198

---
 cftime/__init__.py  |  2 +-
 test/test_cftime.py | 14 ++++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/cftime/__init__.py b/cftime/__init__.py
index b185a0be..49198c68 100644
--- a/cftime/__init__.py
+++ b/cftime/__init__.py
@@ -1,5 +1,5 @@
 from ._cftime import utime, JulianDayFromDate, DateFromJulianDay, UNIT_CONVERSION_FACTORS
-from ._cftime import _parse_date, date2index, time2index
+from ._cftime import _parse_date, date2index, time2index, DATE_TYPES
 from ._cftime import datetime, real_datetime, datetime_base
 from ._cftime import DatetimeNoLeap, DatetimeAllLeap, Datetime360Day, DatetimeJulian, \
                          DatetimeGregorian, DatetimeProlepticGregorian
diff --git a/test/test_cftime.py b/test/test_cftime.py
index 87a1792e..7fb6fd9c 100644
--- a/test/test_cftime.py
+++ b/test/test_cftime.py
@@ -819,6 +819,17 @@ def test_tz_naive(self):
         cal = 'proleptic_gregorian'
         dt2 = num2date(date2num(dt1, units, cal), units, cal)
         assert(dt1 == dt2)
+# issue #198 - cftime.datetime creates calendar specific datetimes that
+# support addition/subtraction of timedeltas.
+        dt = cftime.datetime(2020, 1, 1, calendar='')
+        assert(isinstance(dt, cftime.datetime_base))
+        dt = cftime.datetime(2020, 1, 1, calendar="julian")
+        dt += timedelta(hours=1)
+        assert(str(dt) == '2020-01-01 01:00:00')
+        assert(isinstance(dt, cftime.DatetimeJulian))
+        for cal in cftime.DATE_TYPES.keys():
+            dt = cftime.datetime(2020, 1, 1, calendar=cal)
+            assert(isinstance(dt, cftime.DATE_TYPES[cal]))
 
 
 class TestDate2index(unittest.TestCase):
@@ -1390,8 +1401,7 @@ def test_parse_incorrect_unitstring(self):
                 ValueError, cftime._cftime.date2num, datetime(1900, 1, 1, 0), datestr, 'standard')
 
 
-_DATE_TYPES = [DatetimeNoLeap, DatetimeAllLeap, DatetimeJulian, Datetime360Day,
-               DatetimeGregorian, DatetimeProlepticGregorian]
+_DATE_TYPES = cftime.DATE_TYPES.values()
 
 
 @pytest.fixture(params=_DATE_TYPES)

From 32f5797b63259bca03d35086a6e9f0fd0ef4b5c3 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Mon, 31 Aug 2020 19:50:40 -0600
Subject: [PATCH 09/16] update docstrings

---
 cftime/_cftime.pyx | 51 ++++++++++++++++++++++++++++++++++------------
 1 file changed, 38 insertions(+), 13 deletions(-)

diff --git a/cftime/_cftime.pyx b/cftime/_cftime.pyx
index 1b98b6fe..c2520a62 100644
--- a/cftime/_cftime.pyx
+++ b/cftime/_cftime.pyx
@@ -53,7 +53,7 @@ cdef int32_t* days_per_month_array = [
 _rop_lookup = {Py_LT: '__gt__', Py_LE: '__ge__', Py_EQ: '__eq__',
                Py_GT: '__lt__', Py_GE: '__le__', Py_NE: '__ne__'}
 
-__version__ = '1.2.2'
+__version__ = '1.3.0'
 
 # Adapted from http://delete.me.uk/2005/03/iso8601.html
 # Note: This regex ensures that all ISO8601 timezone formats are accepted - but, due to legacy support for other timestrings, not all incorrect formats can be rejected.
@@ -853,12 +853,25 @@ Create a calendar specific datetime instance.
         date_type = DATE_TYPES[calendar]
         return date_type(year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr)
 
+@cython.embedsignature(True)
 cdef class datetime_base(object):
     """
 The base class implementing most methods of datetime classes that
 mimic datetime.datetime but support calendars other than the proleptic
-Gregorial calendar. The factory function cftime.datetime should be used
+Gregorian calendar. The factory function cftime.datetime should be used
 to create calendar-specific sub-class instances.
+
+Calendar specific sub-classes support timedelta operations by overloading +/-.
+Comparisons with other datetime_base sub-class instances using the same
+calendar are supported.
+Comparison with native python datetime instances is possible
+for cftime.datetime_base sub-class instances using
+'gregorian' and 'proleptic_gregorian' calendars.
+
+Has isoformat, strftime, timetuple, replace, dayofwk, dayofyr, daysinmonth,
+__repr__, and __str__ methods. 
+The default format of the string produced by strftime is controlled by self.format
+(default %Y-%m-%d %H:%M:%S).
     """
     cdef readonly int year, month, day, hour, minute
     cdef readonly int second, microsecond
@@ -1130,6 +1143,10 @@ cdef class DatetimeNoLeap(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "noleap" ("365_day") calendar.
+
+The factory function cftime.datetime should be used
+to create instances of this class using the `calendar` kwarg to specify
+the calendar.
     """
     def __init__(self, *args, **kwargs):
         datetime_base.__init__(self, *args, **kwargs)
@@ -1149,6 +1166,10 @@ cdef class DatetimeAllLeap(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "all_leap" ("366_day") calendar.
+
+The factory function cftime.datetime should be used
+to create instances of this class using the `calendar` kwarg to specify
+the calendar.
     """
     def __init__(self, *args, **kwargs):
         datetime_base.__init__(self, *args, **kwargs)
@@ -1168,6 +1189,10 @@ cdef class Datetime360Day(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "360_day" calendar.
+
+The factory function cftime.datetime should be used
+to create instances of this class using the `calendar` kwarg to specify
+the calendar.
     """
     def __init__(self, *args, **kwargs):
         datetime_base.__init__(self, *args, **kwargs)
@@ -1187,6 +1212,10 @@ cdef class DatetimeJulian(datetime_base):
     """
 Phony datetime object which mimics the python datetime object,
 but uses the "julian" calendar.
+
+The factory function cftime.datetime should be used
+to create instances of this class using the `calendar` kwarg to specify
+the calendar.
     """
     def __init__(self, *args, **kwargs):
         datetime_base.__init__(self, *args, **kwargs)
@@ -1210,6 +1239,10 @@ Instances using the date after 1582-10-15 can be compared to
 datetime.datetime instances and used to compute time differences
 (datetime.timedelta) by subtracting a DatetimeGregorian instance from
 a datetime.datetime instance or vice versa.
+
+The factory function cftime.datetime should be used
+to create instances of this class using the `calendar` kwarg to specify
+the calendar.
     """
     def __init__(self, *args, **kwargs):
         datetime_base.__init__(self, *args, **kwargs)
@@ -1232,17 +1265,9 @@ cdef class DatetimeProlepticGregorian(datetime_base):
 Phony datetime object which mimics the python datetime object,
 but allows for dates that don't exist in the proleptic gregorian calendar.
 
-Supports timedelta operations by overloading + and -.
-
-Has strftime, timetuple, replace, __repr__, and __str__ methods. The
-format of the string produced by __str__ is controlled by self.format
-(default %Y-%m-%d %H:%M:%S). Supports comparisons with other
-datetime instances using the same calendar; comparison with
-native python datetime instances is possible for cftime.datetime_base
-instances using 'gregorian' and 'proleptic_gregorian' calendars.
-
-Instance variables are year,month,day,hour,minute,second,microsecond,dayofwk,dayofyr,
-format, and calendar.
+The factory function cftime.datetime should be used
+to create instances of this class using the `calendar` kwarg to specify
+the calendar.
     """
     def __init__(self, *args, **kwargs):
         datetime_base.__init__(self, *args, **kwargs)

From cb6a78e2872e6e25d944572abf81a0c793bdff7b Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Mon, 31 Aug 2020 19:51:07 -0600
Subject: [PATCH 10/16] update

---
 Changelog | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Changelog b/Changelog
index 16d838e3..c22b42d0 100644
--- a/Changelog
+++ b/Changelog
@@ -1,4 +1,4 @@
-version 1.2.2 (not yet released)
+version 1.3.0 (not yet released)
 ================================
  * zero pad years in strtime (issue #194)
  * have `cftime.datetime` create calendar-specific instances that support

From 3376525312cb233fade7b91635b3644befaf8183 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 5 Sep 2020 16:37:31 -0600
Subject: [PATCH 11/16] update test

---
 test/test_cftime.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/test/test_cftime.py b/test/test_cftime.py
index 7fb6fd9c..dec1cf15 100644
--- a/test/test_cftime.py
+++ b/test/test_cftime.py
@@ -18,6 +18,10 @@
                     DatetimeGregorian, DatetimeJulian, DatetimeNoLeap,
                     DatetimeProlepticGregorian, JulianDayFromDate, _parse_date,
                     date2index, date2num, num2date, utime, UNIT_CONVERSION_FACTORS)
+try:
+    from cftime import datetime_base
+except ImportError:
+    datetime_base = datetime
 
 try:
     from datetime import timezone
@@ -830,6 +834,7 @@ def test_tz_naive(self):
         for cal in cftime.DATE_TYPES.keys():
             dt = cftime.datetime(2020, 1, 1, calendar=cal)
             assert(isinstance(dt, cftime.DATE_TYPES[cal]))
+            assert(isinstance(dt, datetime_base))
 
 
 class TestDate2index(unittest.TestCase):

From 41eb2bf711c2858aa9ec872acaa065b06d6c7e30 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 5 Sep 2020 16:40:17 -0600
Subject: [PATCH 12/16] update

---
 Changelog | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/Changelog b/Changelog
index c22b42d0..b75ac85f 100644
--- a/Changelog
+++ b/Changelog
@@ -3,9 +3,17 @@ version 1.3.0 (not yet released)
  * zero pad years in strtime (issue #194)
  * have `cftime.datetime` create calendar-specific instances that support
    addition and subtraction (issue #198). Name of base class changed
-   from `cftime.datetime` to `cftime.datetime_base` (if your are using 
-   `isinstance(my_datetime, cftime.datetime)` this will need to be changed
-   to `isinstance(my_datetime, cftime.datetime_base)`.
+   from `cftime.datetime` to `cftime.datetime_base` since `cftime.datetime`
+   is not a factory function.  Iif your are using 
+   `isinstance(my_datetime, cftime.datetime` this will need to be changed
+   to `isinstance(my_datetime, cftime.datetime_base)`. To maintain backward
+   compatibility with older versions of cftime, use
+   ```python
+   try:
+       from cftime import datetime_base
+   except ImportError:
+       datetime_base = datetime
+   ```
 
 version 1.2.1 (release tag v1.2.1rel)
 =====================================

From afca28720c994e2beb717559484ceabcfc8c3ac7 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 5 Sep 2020 16:41:47 -0600
Subject: [PATCH 13/16] update

---
 Changelog.md | 1 +
 1 file changed, 1 insertion(+)
 create mode 120000 Changelog.md

diff --git a/Changelog.md b/Changelog.md
new file mode 120000
index 00000000..58bc9728
--- /dev/null
+++ b/Changelog.md
@@ -0,0 +1 @@
+Changelog
\ No newline at end of file

From 7d757644bfc54f2a8205b5a06bc9197a303f2846 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 5 Sep 2020 16:42:30 -0600
Subject: [PATCH 14/16] update

---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 3f883c0e..c27b9394 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Time-handling functionality from netcdf4-python
 [![Commits Status](https://img.shields.io/github/commits-since/UniData/cftime/latest.svg)](https://github.com/UniData/cftime/commits/master)
 
 ## News
-For details on the latest updates, see the [Changelog](https://github.com/Unidata/cftime/blob/master/Changelog).
+For details on the latest updates, see the [Changelog](https://github.com/Unidata/cftime/blob/master/Changelog.md).
 
 07/20/2020: Version 1.2.1 released.  Fixes a couple of regressions introduced in 1.2.0. See Changelog for details.
 

From c5c2369d0edffc370cc0f94b696ec95acdae00a6 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 5 Sep 2020 16:45:46 -0600
Subject: [PATCH 15/16] update

---
 Changelog.md | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 100 insertions(+), 1 deletion(-)
 mode change 120000 => 100644 Changelog.md

diff --git a/Changelog.md b/Changelog.md
deleted file mode 120000
index 58bc9728..00000000
--- a/Changelog.md
+++ /dev/null
@@ -1 +0,0 @@
-Changelog
\ No newline at end of file
diff --git a/Changelog.md b/Changelog.md
new file mode 100644
index 00000000..b75ac85f
--- /dev/null
+++ b/Changelog.md
@@ -0,0 +1,100 @@
+version 1.3.0 (not yet released)
+================================
+ * zero pad years in strtime (issue #194)
+ * have `cftime.datetime` create calendar-specific instances that support
+   addition and subtraction (issue #198). Name of base class changed
+   from `cftime.datetime` to `cftime.datetime_base` since `cftime.datetime`
+   is not a factory function.  Iif your are using 
+   `isinstance(my_datetime, cftime.datetime` this will need to be changed
+   to `isinstance(my_datetime, cftime.datetime_base)`. To maintain backward
+   compatibility with older versions of cftime, use
+   ```python
+   try:
+       from cftime import datetime_base
+   except ImportError:
+       datetime_base = datetime
+   ```
+
+version 1.2.1 (release tag v1.2.1rel)
+=====================================
+ * num2date uses 'proleptic_gregorian' scheme when basedate is post-Gregorian but date is pre-Gregorian
+   (issue #182).
+ * fix 1.2.0 regression (date2num no longer works with numpy scalar array inputs, issue #185).
+ * Fix for issue #187 (have date2num round to the nearest second when within 1
+   microsecond).
+ * Fix for issue #189 (leap years calculated incorrectly for negative years in
+   proleptic_gregorian calendar).
+
+version 1.2.0 (release tag v1.2.0rel)
+=====================================
+ * Return the default values of dayofwk and dayofyr when calendar
+   is '' (issue #173).
+ * fix treatment of masked arrays in num2date and date2num (issue #175).
+   Also make sure masked arrays are output from num2date/date2num if
+   masked arrays are input.
+ * Where possible, use timedelta arithmetic to decode times exactly within
+   num2date (issue #171).
+ * Make taking the difference between two cftime datetimes to produce a
+   timedelta exact to the microsecond; depending on the units encoding,
+   this enables date2num to be exact as well (issue #109).
+ * utime.date2num/utime.num2date now just call module level functions.
+   JulianDayFromDate/DateFromJulianDay no longer used internally (PR #180).
+
+
+version 1.1.3 (release tag v1.1.3rel)
+=====================================
+ * add isoformat method for compatibility with python datetime (issue #152).
+ * make 'standard' default calendar for cftime.datetime
+   so that dayofwk,dayofyr methods don't fail (issue #169).
+
+version 1.1.2 (release tag v1.1.2rel)
+=====================================
+ * change dayofwk and dayofyr attributes into properties (issue #158)
+ * fix for issue #165 (python datetime should be returned when
+   only_use_cftime_datetimes=False).
+
+version 1.1.1.2 (release tag v1.1.1.2rel)
+=========================================
+ * include pyproject.toml in MANIFEST.in so it gets 
+   included in source tarball (issue #154).
+
+version 1.1.1.1 (release tag v1.1.1.1rel)
+=========================================
+ * Fix error installing with pip on python 3.8 by following 
+   PEP 517 (issue #148, PR #149)
+
+version 1.1.1 (release tag v1.1.1rel)
+=====================================
+
+ * fix microsecond formatting issue, ensure identical results
+   computed for arrays and scales (issue #143, PR #146).
+
+version 1.1.0 (release tag v1.1.0rel)
+=====================================
+
+ * improved exceptions for time differences (issue #128, PR #131).
+
+ * fix intersphinx entries (issue #133, PR #133)
+
+ * make only_use_cftime_datetimes=True by default, so cftime datetime
+   instances are returned by default by num2date (instead of returning python
+   datetime instances where possible). Issue #136, PR #135.
+
+ * Add daysinmonth attribute (issue #137, PR #138).
+
+ * If only_use_python_datetimes=True and only_use_cftime_datetimes=False,
+   num2date only returns python datetime instances and raises an exception
+   if this is not possible.  num2pydate convenience function added which just calls
+   num2date with only_use_python_datetimes=True and
+   only_use_cftime_datetimes=False.
+   Remove positive times check, raise ValueError if python datetime
+   tries to compute a date before MINYEAR (issue #134, PR #139)
+
+ * Fix for fractional seconds in reference date in units string (issue #140,
+   PR # 141).
+
+version 1.0.4.2 release
+=======================
+
+ * fix for issue #126 (date2num error when converting a DatetimeProlepticGregorian 
+   object). PR #127.

From 449be55572e76b3de5252e932e1274b584e9bec5 Mon Sep 17 00:00:00 2001
From: Jeff Whitaker <jswhit@fastmail.fm>
Date: Sat, 5 Sep 2020 16:47:15 -0600
Subject: [PATCH 16/16] revert

---
 Changelog.md | 100 ---------------------------------------------------
 README.md    |   2 +-
 2 files changed, 1 insertion(+), 101 deletions(-)
 delete mode 100644 Changelog.md

diff --git a/Changelog.md b/Changelog.md
deleted file mode 100644
index b75ac85f..00000000
--- a/Changelog.md
+++ /dev/null
@@ -1,100 +0,0 @@
-version 1.3.0 (not yet released)
-================================
- * zero pad years in strtime (issue #194)
- * have `cftime.datetime` create calendar-specific instances that support
-   addition and subtraction (issue #198). Name of base class changed
-   from `cftime.datetime` to `cftime.datetime_base` since `cftime.datetime`
-   is not a factory function.  Iif your are using 
-   `isinstance(my_datetime, cftime.datetime` this will need to be changed
-   to `isinstance(my_datetime, cftime.datetime_base)`. To maintain backward
-   compatibility with older versions of cftime, use
-   ```python
-   try:
-       from cftime import datetime_base
-   except ImportError:
-       datetime_base = datetime
-   ```
-
-version 1.2.1 (release tag v1.2.1rel)
-=====================================
- * num2date uses 'proleptic_gregorian' scheme when basedate is post-Gregorian but date is pre-Gregorian
-   (issue #182).
- * fix 1.2.0 regression (date2num no longer works with numpy scalar array inputs, issue #185).
- * Fix for issue #187 (have date2num round to the nearest second when within 1
-   microsecond).
- * Fix for issue #189 (leap years calculated incorrectly for negative years in
-   proleptic_gregorian calendar).
-
-version 1.2.0 (release tag v1.2.0rel)
-=====================================
- * Return the default values of dayofwk and dayofyr when calendar
-   is '' (issue #173).
- * fix treatment of masked arrays in num2date and date2num (issue #175).
-   Also make sure masked arrays are output from num2date/date2num if
-   masked arrays are input.
- * Where possible, use timedelta arithmetic to decode times exactly within
-   num2date (issue #171).
- * Make taking the difference between two cftime datetimes to produce a
-   timedelta exact to the microsecond; depending on the units encoding,
-   this enables date2num to be exact as well (issue #109).
- * utime.date2num/utime.num2date now just call module level functions.
-   JulianDayFromDate/DateFromJulianDay no longer used internally (PR #180).
-
-
-version 1.1.3 (release tag v1.1.3rel)
-=====================================
- * add isoformat method for compatibility with python datetime (issue #152).
- * make 'standard' default calendar for cftime.datetime
-   so that dayofwk,dayofyr methods don't fail (issue #169).
-
-version 1.1.2 (release tag v1.1.2rel)
-=====================================
- * change dayofwk and dayofyr attributes into properties (issue #158)
- * fix for issue #165 (python datetime should be returned when
-   only_use_cftime_datetimes=False).
-
-version 1.1.1.2 (release tag v1.1.1.2rel)
-=========================================
- * include pyproject.toml in MANIFEST.in so it gets 
-   included in source tarball (issue #154).
-
-version 1.1.1.1 (release tag v1.1.1.1rel)
-=========================================
- * Fix error installing with pip on python 3.8 by following 
-   PEP 517 (issue #148, PR #149)
-
-version 1.1.1 (release tag v1.1.1rel)
-=====================================
-
- * fix microsecond formatting issue, ensure identical results
-   computed for arrays and scales (issue #143, PR #146).
-
-version 1.1.0 (release tag v1.1.0rel)
-=====================================
-
- * improved exceptions for time differences (issue #128, PR #131).
-
- * fix intersphinx entries (issue #133, PR #133)
-
- * make only_use_cftime_datetimes=True by default, so cftime datetime
-   instances are returned by default by num2date (instead of returning python
-   datetime instances where possible). Issue #136, PR #135.
-
- * Add daysinmonth attribute (issue #137, PR #138).
-
- * If only_use_python_datetimes=True and only_use_cftime_datetimes=False,
-   num2date only returns python datetime instances and raises an exception
-   if this is not possible.  num2pydate convenience function added which just calls
-   num2date with only_use_python_datetimes=True and
-   only_use_cftime_datetimes=False.
-   Remove positive times check, raise ValueError if python datetime
-   tries to compute a date before MINYEAR (issue #134, PR #139)
-
- * Fix for fractional seconds in reference date in units string (issue #140,
-   PR # 141).
-
-version 1.0.4.2 release
-=======================
-
- * fix for issue #126 (date2num error when converting a DatetimeProlepticGregorian 
-   object). PR #127.
diff --git a/README.md b/README.md
index c27b9394..3f883c0e 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Time-handling functionality from netcdf4-python
 [![Commits Status](https://img.shields.io/github/commits-since/UniData/cftime/latest.svg)](https://github.com/UniData/cftime/commits/master)
 
 ## News
-For details on the latest updates, see the [Changelog](https://github.com/Unidata/cftime/blob/master/Changelog.md).
+For details on the latest updates, see the [Changelog](https://github.com/Unidata/cftime/blob/master/Changelog).
 
 07/20/2020: Version 1.2.1 released.  Fixes a couple of regressions introduced in 1.2.0. See Changelog for details.