Fix invalid relativedelta_kwds

doc/source/whatsnew/v0.23.0.txt

@@ -1245,7 +1245,6 @@ Offsets
 - Bug in :class:`FY5253` where ``datetime`` addition and subtraction incremented incorrectly for dates on the year-end but not normalized to midnight (:issue:`18854`)
 - Bug in :class:`FY5253` where date offsets could incorrectly raise an ``AssertionError`` in arithmetic operations (:issue:`14774`)
 
-
 Numeric
 ^^^^^^^
 - Bug in :class:`Series` constructor with an int or float list where specifying ``dtype=str``, ``dtype='str'`` or ``dtype='U'`` failed to convert the data elements to strings (:issue:`16605`)

doc/source/whatsnew/v0.24.0.txt

@@ -402,7 +402,8 @@ Timezones
 Offsets
 ^^^^^^^
 
--
+- Bug in :class:`FY5253` where date offsets could incorrectly raise an ``AssertionError`` in arithmetic operatons (:issue:`14774`)
+- Bug in :class:`DateOffset` where keyword arguments ``week`` and ``milliseconds`` were accepted and ignored.  Passing these will now raise ``ValueError`` (:issue:`19398`)
 -
 
 Numeric

pandas/_libs/tslibs/offsets.pyx

@@ -254,10 +254,10 @@ def _validate_business_time(t_input):
 
 relativedelta_kwds = set([
     'years', 'months', 'weeks', 'days',
-    'year', 'month', 'week', 'day', 'weekday',
+    'year', 'month', 'day', 'weekday',
     'hour', 'minute', 'second', 'microsecond',
     'nanosecond', 'nanoseconds',
-    'hours', 'minutes', 'seconds', 'milliseconds', 'microseconds'])
+    'hours', 'minutes', 'seconds', 'microseconds'])
 
 
 def _determine_offset(kwds):

pandas/tests/tseries/offsets/test_offsets.py

@@ -3085,6 +3085,13 @@ def test_valid_month_attributes(kwd, month_classes):
         cls(**{kwd: 3})
 
 
+@pytest.mark.parametrize('kwd', sorted(list(liboffsets.relativedelta_kwds)))
+def test_valid_relativedelta_kwargs(kwd):
+    # Check that all the arguments specified in liboffsets.relativedelta_kwds
+    # are in fact valid relativedelta keyword args
+    DateOffset(**{kwd: 1})
+
+
 @pytest.mark.parametrize('kwd', sorted(list(liboffsets.relativedelta_kwds)))
 def test_valid_tick_attributes(kwd, tick_classes):
     # GH#18226

pandas/tseries/offsets.py

@@ -158,6 +158,54 @@ def __add__(date):
     date + BDay(0) == BDay.rollforward(date)
 
     Since 0 is a bit weird, we suggest avoiding its use.
+
+    Parameters
+    ----------
+    n : int, default 1
+        The number of time periods the offset represents.
+    normalize : bool, default False
+        Whether to round the result of a DateOffset addition down to the
+        previous midnight.
+    **kwds
+        Temporal parameter that add to or replace the offset value.
+
+        Parameters that **add** to the offset (like Timedelta):
+
+        - years
+        - months
+        - weeks
+        - days
+        - hours
+        - minutes
+        - seconds
+        - microseconds
+        - nanoseconds
+
+        Parameters that **replace** the offset value:
+
+        - year
+        - month
+        - day
+        - weekday
+        - hour
+        - minute
+        - second
+        - microsecond
+        - nanosecond
+
+    See Also
+    --------
+    dateutil.relativedelta.relativedelta
+
+    Examples
+    --------
+    >>> ts = pd.Timestamp('2017-01-01 09:10:11')
+    >>> ts + DateOffset(months=3)
+    Timestamp('2017-04-01 09:10:11')
+
+    >>> ts = pd.Timestamp('2017-01-01 09:10:11')
+    >>> ts + DateOffset(month=3)
+    Timestamp('2017-03-01 09:10:11')
     """
     _params = cache_readonly(BaseOffset._params.fget)
     _use_relativedelta = False