Support is_dst indicators in tz_localize

doc/source/timeseries.rst

@@ -1357,6 +1357,9 @@ Pandas provides rich support for working with timestamps in different time zones
 ``dateutil`` support is new [in 0.14.1] and currently only supported for fixed offset and tzfile zones. The default library is ``pytz``.
 Support for ``dateutil`` is provided for compatibility with other applications e.g. if you use ``dateutil`` in other python packages.
 
+Working with Time Zones
+~~~~~~~~~~~~~~~~~~~~~~~
+
 By default, pandas objects are time zone unaware:
 
 .. ipython:: python
@@ -1488,10 +1491,29 @@ TimeSeries, aligning the data on the UTC timestamps:
    result
    result.index
 
+To remove timezone from tz-aware ``DatetimeIndex``, use ``tz_localize(None)`` or ``tz_convert(None)``. 
+``tz_localize(None)`` will remove timezone holding local time representations. 
+``tz_convert(None)`` will remove timezone after converting to UTC time.
+
+.. ipython:: python
+
+   didx = DatetimeIndex(start='2014-08-01 09:00', freq='H', periods=10, tz='US/Eastern')
+   didx
+   didx.tz_localize(None)
+   didx.tz_convert(None)
+
+   # tz_convert(None) is identical with tz_convert('UTC').tz_localize(None)
+   didx.tz_convert('UCT').tz_localize(None)
+
+.. _timeseries.timezone_ambiguous:
+
+Ambiguous Times when Localizing
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 In some cases, localize cannot determine the DST and non-DST hours when there are
-duplicates.  This often happens when reading files that simply duplicate the hours.
-The infer_dst argument in tz_localize will attempt
-to determine the right offset.
+duplicates.  This often happens when reading files or database records that simply 
+duplicate the hours.  Passing ``ambiguous='infer'`` (``infer_dst`` argument in prior
+releases) into ``tz_localize`` will attempt to determine the right offset.
 
 .. ipython:: python
    :okexcept:
@@ -1500,21 +1522,23 @@ to determine the right offset.
                                '11/06/2011 01:00', '11/06/2011 02:00',
                                '11/06/2011 03:00'])
    rng_hourly.tz_localize('US/Eastern')
-   rng_hourly_eastern = rng_hourly.tz_localize('US/Eastern', infer_dst=True)
+   rng_hourly_eastern = rng_hourly.tz_localize('US/Eastern', ambiguous='infer')
    rng_hourly_eastern.values
 
-
-To remove timezone from tz-aware ``DatetimeIndex``, use ``tz_localize(None)`` or ``tz_convert(None)``. ``tz_localize(None)`` will remove timezone holding local time representations. ``tz_convert(None)`` will remove timezone after converting to UTC time.
+In addition to 'infer', there are several other arguments supported.  Passing
+an array-like of bools or 0s/1s where True represents a DST hour and False a 
+non-DST hour, allows for distinguishing more than one DST 
+transition (e.g., if you have multiple records in a database each with their 
+own DST transition).  Or passing 'NaT' will fill in transition times
+with not-a-time values.  These methods are available in the ``DatetimeIndex``
+constructor as well as ``tz_localize``.
 
 .. ipython:: python
+
+   rng_hourly_dst = np.array([1, 1, 0, 0, 0])
+   rng_hourly.tz_localize('US/Eastern', ambiguous=rng_hourly_dst).values
+   rng_hourly.tz_localize('US/Eastern', ambiguous='NaT').values
 
-   didx = DatetimeIndex(start='2014-08-01 09:00', freq='H', periods=10, tz='US/Eastern')
-   didx
-   didx.tz_localize(None)
-   didx.tz_convert(None)
-
-   # tz_convert(None) is identical with tz_convert('UTC').tz_localize(None)
-   didx.tz_convert('UCT').tz_localize(None)
 
 .. _timeseries.timedeltas:
 

doc/source/v0.15.0.txt

@@ -344,7 +344,6 @@ API changes
 - ``Series.to_csv()`` now returns a string when ``path=None``, matching the behaviour of
     ``DataFrame.to_csv()`` (:issue:`8215`).
 
-
 .. _whatsnew_0150.index_set_ops:
 
 - The Index set operations ``+`` and ``-`` were deprecated in order to provide these for numeric type operations on certain index types. ``+`` can be replace by ``.union()`` or ``|``, and ``-`` by ``.difference()``. Further the method name ``Index.diff()`` is deprecated and can be replaced by ``Index.difference()`` (:issue:`8226`)
@@ -466,6 +465,10 @@ Deprecations
 
 - The ``convert_dummies`` method has been deprecated in favor of
   ``get_dummies`` (:issue:`8140`)
+- The ``infer_dst`` argument in ``tz_localize`` will be deprecated in favor of
+  ``ambiguous`` to allow for more flexibility in dealing with DST transitions.
+  Replace ``infer_dst=True`` with ``ambiguous='infer'`` for the same behavior (:issue:`7943`).
+  See :ref:`the docs<timeseries.timezone_ambiguous>` for more details.
 
 .. _whatsnew_0150.knownissues:
 
@@ -544,7 +547,10 @@ Enhancements
 
 
 
-
+- ``tz_localize`` now accepts the ``ambiguous`` keyword which allows for passing an array of bools 
+  indicating whether the date belongs in DST or not, 'NaT' for setting transition times to NaT, 
+  'infer' for inferring DST/non-DST, and 'raise' (default) for an AmbiguousTimeError to be raised (:issue:`7943`).
+  See :ref:`the docs<timeseries.timezone_ambiguous>` for more details.
 
 
 

pandas/core/generic.py

@@ -23,7 +23,7 @@
                                 _maybe_box_datetimelike, ABCSeries,
                                 SettingWithCopyError, SettingWithCopyWarning)
 import pandas.core.nanops as nanops
-from pandas.util.decorators import Appender, Substitution
+from pandas.util.decorators import Appender, Substitution, deprecate_kwarg
 from pandas.core import config
 
 # goal is to be able to define the docs close to function, while still being
@@ -3558,8 +3558,11 @@ def _tz_convert(ax, tz):
         result = self._constructor(self._data, copy=copy)
         result.set_axis(axis,ax)
         return result.__finalize__(self)
-
-    def tz_localize(self, tz, axis=0, level=None, copy=True, infer_dst=False):
+
+    @deprecate_kwarg(old_arg_name='infer_dst', new_arg_name='ambiguous',
+                     mapping={True: 'infer', False: 'raise'})
+    def tz_localize(self, tz, axis=0, level=None, copy=True, 
+                    ambiguous='raise'):
         """
         Localize tz-naive TimeSeries to target time zone
 
@@ -3572,16 +3575,22 @@ def tz_localize(self, tz, axis=0, level=None, copy=True, infer_dst=False):
             must be None
         copy : boolean, default True
             Also make a copy of the underlying data
-        infer_dst : boolean, default False
-            Attempt to infer fall dst-transition times based on order
-
+        ambiguous : 'infer', bool-ndarray, 'NaT', default 'raise'
+            - 'infer' will attempt to infer fall dst-transition hours based on order
+            - bool-ndarray where True signifies a DST time, False designates
+              a non-DST time (note that this flag is only applicable for ambiguous times)
+            - 'NaT' will return NaT where there are ambiguous times
+            - 'raise' will raise an AmbiguousTimeError if there are ambiguous times
+        infer_dst : boolean, default False (DEPRECATED)
+            Attempt to infer fall dst-transition hours based on order
+
         Returns
         -------
         """
         axis = self._get_axis_number(axis)
         ax = self._get_axis(axis)
 
-        def _tz_localize(ax, tz, infer_dst):
+        def _tz_localize(ax, tz, ambiguous):
             if not hasattr(ax, 'tz_localize'):
                 if len(ax) > 0:
                     ax_name = self._get_axis_name(axis)
@@ -3590,19 +3599,19 @@ def _tz_localize(ax, tz, infer_dst):
                 else:
                     ax = DatetimeIndex([],tz=tz)
             else:
-                ax = ax.tz_localize(tz, infer_dst=infer_dst)
+                ax = ax.tz_localize(tz, ambiguous=ambiguous)
             return ax
 
         # if a level is given it must be a MultiIndex level or
         # equivalent to the axis name
         if isinstance(ax, MultiIndex):
             level = ax._get_level_number(level)
-            new_level = _tz_localize(ax.levels[level], tz, infer_dst)
+            new_level = _tz_localize(ax.levels[level], tz, ambiguous)
             ax = ax.set_levels(new_level, level=level)
         else:
             if level not in (None, 0, ax.name):
                 raise ValueError("The level {0} is not valid".format(level))
-            ax =  _tz_localize(ax, tz, infer_dst)
+            ax =  _tz_localize(ax, tz, ambiguous)
 
         result = self._constructor(self._data, copy=copy)
         result.set_axis(axis,ax)

pandas/tseries/index.py

@@ -6,6 +6,8 @@
 
 import numpy as np
 
+import warnings
+
 from pandas.core.common import (_NS_DTYPE, _INT64_DTYPE,
                                 _values_from_object, _maybe_box,
                                 ABCSeries)
@@ -18,7 +20,7 @@
 from pandas.core.base import DatetimeIndexOpsMixin
 from pandas.tseries.offsets import DateOffset, generate_range, Tick, CDay
 from pandas.tseries.tools import parse_time_string, normalize_date
-from pandas.util.decorators import cache_readonly
+from pandas.util.decorators import cache_readonly, deprecate_kwarg
 import pandas.core.common as com
 import pandas.tseries.offsets as offsets
 import pandas.tseries.tools as tools
@@ -145,6 +147,15 @@ class DatetimeIndex(DatetimeIndexOpsMixin, Int64Index):
     closed : string or None, default None
         Make the interval closed with respect to the given frequency to
         the 'left', 'right', or both sides (None)
+    tz : pytz.timezone or dateutil.tz.tzfile
+    ambiguous : 'infer', bool-ndarray, 'NaT', default 'raise'
+        - 'infer' will attempt to infer fall dst-transition hours based on order
+        - bool-ndarray where True signifies a DST time, False signifies
+          a non-DST time (note that this flag is only applicable for ambiguous times)
+        - 'NaT' will return NaT where there are ambiguous times
+        - 'raise' will raise an AmbiguousTimeError if there are ambiguous times
+    infer_dst : boolean, default False (DEPRECATED)
+        Attempt to infer fall dst-transition hours based on order
     name : object
         Name to be stored in the index
     """
@@ -180,15 +191,17 @@ class DatetimeIndex(DatetimeIndexOpsMixin, Int64Index):
                          'is_quarter_start','is_quarter_end','is_year_start','is_year_end']
     _is_numeric_dtype = False
 
+
+    @deprecate_kwarg(old_arg_name='infer_dst', new_arg_name='ambiguous',
+                     mapping={True: 'infer', False: 'raise'})
     def __new__(cls, data=None,
                 freq=None, start=None, end=None, periods=None,
                 copy=False, name=None, tz=None,
                 verify_integrity=True, normalize=False,
-                closed=None, **kwargs):
+                closed=None, ambiguous='raise', **kwargs):
 
         dayfirst = kwargs.pop('dayfirst', None)
         yearfirst = kwargs.pop('yearfirst', None)
-        infer_dst = kwargs.pop('infer_dst', False)
 
         freq_infer = False
         if not isinstance(freq, DateOffset):
@@ -214,7 +227,7 @@ def __new__(cls, data=None,
         if data is None:
             return cls._generate(start, end, periods, name, freq,
                                  tz=tz, normalize=normalize, closed=closed,
-                                 infer_dst=infer_dst)
+                                 ambiguous=ambiguous)
 
         if not isinstance(data, (np.ndarray, Index, ABCSeries)):
             if np.isscalar(data):
@@ -240,7 +253,7 @@ def __new__(cls, data=None,
                         data.name = name
 
                     if tz is not None:
-                        return data.tz_localize(tz, infer_dst=infer_dst)
+                        return data.tz_localize(tz, ambiguous=ambiguous)
 
                     return data
 
@@ -309,7 +322,7 @@ def __new__(cls, data=None,
                     # Convert tz-naive to UTC
                     ints = subarr.view('i8')
                     subarr = tslib.tz_localize_to_utc(ints, tz,
-                                                      infer_dst=infer_dst)
+                                                      ambiguous=ambiguous)
 
                 subarr = subarr.view(_NS_DTYPE)
 
@@ -333,7 +346,7 @@ def __new__(cls, data=None,
 
     @classmethod
     def _generate(cls, start, end, periods, name, offset,
-                  tz=None, normalize=False, infer_dst=False, closed=None):
+                  tz=None, normalize=False, ambiguous='raise', closed=None):
         if com._count_not_none(start, end, periods) != 2:
             raise ValueError('Must specify two of start, end, or periods')
 
@@ -447,7 +460,7 @@ def _generate(cls, start, end, periods, name, offset,
 
             if tz is not None and getattr(index, 'tz', None) is None:
                 index = tslib.tz_localize_to_utc(com._ensure_int64(index), tz,
-                                                 infer_dst=infer_dst)
+                                                 ambiguous=ambiguous)
                 index = index.view(_NS_DTYPE)
 
         index = cls._simple_new(index, name=name, freq=offset, tz=tz)
@@ -1645,7 +1658,9 @@ def tz_convert(self, tz):
         # No conversion since timestamps are all UTC to begin with
         return self._shallow_copy(tz=tz)
 
-    def tz_localize(self, tz, infer_dst=False):
+    @deprecate_kwarg(old_arg_name='infer_dst', new_arg_name='ambiguous',
+                 mapping={True: 'infer', False: 'raise'})
+    def tz_localize(self, tz, ambiguous='raise'):
         """
         Localize tz-naive DatetimeIndex to given time zone (using pytz/dateutil),
         or remove timezone from tz-aware DatetimeIndex
@@ -1656,7 +1671,13 @@ def tz_localize(self, tz, infer_dst=False):
             Time zone for time. Corresponding timestamps would be converted to
             time zone of the TimeSeries.
             None will remove timezone holding local time.
-        infer_dst : boolean, default False
+        ambiguous : 'infer', bool-ndarray, 'NaT', default 'raise'
+            - 'infer' will attempt to infer fall dst-transition hours based on order
+            - bool-ndarray where True signifies a DST time, False signifies
+              a non-DST time (note that this flag is only applicable for ambiguous times)
+            - 'NaT' will return NaT where there are ambiguous times
+            - 'raise' will raise an AmbiguousTimeError if there are ambiguous times
+        infer_dst : boolean, default False (DEPRECATED)
             Attempt to infer fall dst-transition hours based on order
 
         Returns
@@ -1671,7 +1692,9 @@ def tz_localize(self, tz, infer_dst=False):
         else:
             tz = tslib.maybe_get_tz(tz)
             # Convert to UTC
-            new_dates = tslib.tz_localize_to_utc(self.asi8, tz, infer_dst=infer_dst)
+
+            new_dates = tslib.tz_localize_to_utc(self.asi8, tz, 
+                                                 ambiguous=ambiguous)
         new_dates = new_dates.view(_NS_DTYPE)
         return self._shallow_copy(new_dates, tz=tz)