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DatetimeIndex.tz_localize(*args, **kwargs)[source]

Localize tz-naive Datetime Array/Index to tz-aware Datetime Array/Index.

This method takes a time zone (tz) naive Datetime Array/Index object and makes this time zone aware. It does not move the time to another time zone. Time zone localization helps to switch from time zone aware to time zone unaware objects.


tz : string, pytz.timezone, or None

Time zone to convert timestamps to. Passing None will remove the time zone information preserving local time.

ambiguous : ‘infer’, ‘NaT’, bool array, default ‘raise’

When clocks moved backward due to DST, ambiguous times may arise. For example in Central European Time (UTC+01), when going from 03:00 DST to 02:00 non-DST, 02:30:00 local time occurs both at 00:30:00 UTC and at 01:30:00 UTC. In such a situation, the ambiguous parameter dictates how ambiguous times should be handled.

  • ‘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

nonexistent : ‘shift’, ‘NaT’ default ‘raise’

A nonexistent time does not exist in a particular timezone where clocks moved forward due to DST.

  • ‘shift’ will shift the nonexistent times forward to the closest existing time
  • ‘NaT’ will return NaT where there are nonexistent times
  • ‘raise’ will raise an NonExistentTimeError if there are nonexistent times

New in version 0.24.0.

errors : {‘raise’, ‘coerce’}, default None

  • ‘raise’ will raise a NonExistentTimeError if a timestamp is not valid in the specified time zone (e.g. due to a transition from or to DST time). Use nonexistent='raise' instead.
  • ‘coerce’ will return NaT if the timestamp can not be converted to the specified time zone. Use nonexistent='NaT' instead.

Deprecated since version 0.24.0.


result : same type as self

Array/Index converted to the specified time zone.



If the Datetime Array/Index is tz-aware and tz is not None.

See also

Convert tz-aware DatetimeIndex from one time zone to another.


>>> tz_naive = pd.date_range('2018-03-01 09:00', periods=3)
>>> tz_naive
DatetimeIndex(['2018-03-01 09:00:00', '2018-03-02 09:00:00',
               '2018-03-03 09:00:00'],
              dtype='datetime64[ns]', freq='D')

Localize DatetimeIndex in US/Eastern time zone:

>>> tz_aware = tz_naive.tz_localize(tz='US/Eastern')
>>> tz_aware
DatetimeIndex(['2018-03-01 09:00:00-05:00',
               '2018-03-02 09:00:00-05:00',
               '2018-03-03 09:00:00-05:00'],
              dtype='datetime64[ns, US/Eastern]', freq='D')

With the tz=None, we can remove the time zone information while keeping the local time (not converted to UTC):

>>> tz_aware.tz_localize(None)
DatetimeIndex(['2018-03-01 09:00:00', '2018-03-02 09:00:00',
               '2018-03-03 09:00:00'],
              dtype='datetime64[ns]', freq='D')

Be careful with DST changes. When there is sequential data, pandas can infer the DST time: >>> s = pd.to_datetime(pd.Series([ … ‘2018-10-28 01:30:00’, … ‘2018-10-28 02:00:00’, … ‘2018-10-28 02:30:00’, … ‘2018-10-28 02:00:00’, … ‘2018-10-28 02:30:00’, … ‘2018-10-28 03:00:00’, … ‘2018-10-28 03:30:00’])) >>> s.dt.tz_localize(‘CET’, ambiguous=’infer’) 2018-10-28 01:30:00+02:00 0 2018-10-28 02:00:00+02:00 1 2018-10-28 02:30:00+02:00 2 2018-10-28 02:00:00+01:00 3 2018-10-28 02:30:00+01:00 4 2018-10-28 03:00:00+01:00 5 2018-10-28 03:30:00+01:00 6 dtype: int64

In some cases, inferring the DST is impossible. In such cases, you can pass an ndarray to the ambiguous parameter to set the DST explicitly

>>> s = pd.to_datetime(pd.Series([
... '2018-10-28 01:20:00',
... '2018-10-28 02:36:00',
... '2018-10-28 03:46:00']))
>>> s.dt.tz_localize('CET', ambiguous=np.array([True, True, False]))
0   2018-10-28 01:20:00+02:00
1   2018-10-28 02:36:00+02:00
2   2018-10-28 03:46:00+01:00
dtype: datetime64[ns, CET]
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