ENH: Support parsing <Month Name> <Day number> e.g. Jan 1 in date utilities

[TomAugspurger]

I assume that this was officially supported before. Haven't narrowed it down any more than sometime between 0.16.2 and 0.17.0.

In [1]: pd.__version__
Out[1]: '0.16.2'

In [2]: pd.date_range("Jan 1", "March 31", name="date")
Out[2]:
DatetimeIndex(['2015-01-01', '2015-01-02', '2015-01-03', '2015-01-04',
               '2015-01-05', '2015-01-06', '2015-01-07', '2015-01-08',
               '2015-01-09', '2015-01-10', '2015-01-11', '2015-01-12',
...

In [1]: pd.__version__
Out[1]: '0.17.0'

In [2]: pd.date_range("Jan 1", "March 31", name="date")
---------------------------------------------------------------------------
OutOfBoundsDatetime                       Traceback (most recent call last)
<ipython-input-2-8eaca08051ac> in <module>()
----> 1 pd.date_range("Jan 1", "March 31", name="date")

/Users/tom.augspurger/Envs/py3/lib/python3.5/site-packages/pandas/tseries/index.py in date_range(start, end, periods, freq, tz, normalize, name, closed)
   1912     return DatetimeIndex(start=start, end=end, periods=periods,
   1913                          freq=freq, tz=tz, normalize=normalize, name=name,
-> 1914                          closed=closed)
   1915
   1916

/Users/tom.augspurger/Envs/py3/lib/python3.5/site-packages/pandas/util/decorators.py in wrapper(*args, **kwargs)
     87                 else:
     88                     kwargs[new_arg_name] = new_arg_value
---> 89             return func(*args, **kwargs)
     90         return wrapper
     91     return _deprecate_kwarg

/Users/tom.augspurger/Envs/py3/lib/python3.5/site-packages/pandas/tseries/index.py in __new__(cls, data, freq, start, end, periods, copy, name, tz, verify_integrity, normalize, closed, ambiguous, dtype, **kwargs)
    234             return cls._generate(start, end, periods, name, freq,
    235                                  tz=tz, normalize=normalize, closed=closed,
--> 236                                  ambiguous=ambiguous)
    237
    238         if not isinstance(data, (np.ndarray, Index, ABCSeries)):

/Users/tom.augspurger/Envs/py3/lib/python3.5/site-packages/pandas/tseries/index.py in _generate(cls, start, end, periods, name, offset, tz, normalize, ambiguous, closed)
    383
    384         if start is not None:
--> 385             start = Timestamp(start)
    386
    387         if end is not None:

pandas/tslib.pyx in pandas.tslib.Timestamp.__new__ (pandas/tslib.c:8967)()

pandas/tslib.pyx in pandas.tslib.convert_to_tsobject (pandas/tslib.c:22303)()

pandas/tslib.pyx in pandas.tslib.convert_str_to_tsobject (pandas/tslib.c:24364)()

pandas/tslib.pyx in pandas.tslib.convert_to_tsobject (pandas/tslib.c:23344)()

pandas/tslib.pyx in pandas.tslib._check_dts_bounds (pandas/tslib.c:26590)()

OutOfBoundsDatetime: Out of bounds nanosecond timestamp: 1-01-01 00:00:00

[TomAugspurger]

Never mind. Never documented.

[jorisvandenbossche]

@jreback commented here mwaskom/seaborn#702 (comment) it was never meant to be supported

[jorisvandenbossche]

Further, @jreback, I thought it was maybe not a written rule, but still somewhat generally assumed that pandas did fall back to dateutil.parser.parse if it couldn't parse the datetime itself. So in that sense, it is somewhat surprising to me pd.to_datetime('Jan 1') no longer works

[jreback]

this has to do with the change IIRC @sinhrks, e.g. #7599 made to make all parsing consistent.

I think this did work (though not officially / undoced / not tested). So we prob can support it. But should have a real effort here.

[sinhrks]

I think 0.17 behavior is consistent, but allowing to pass default datetime (today's date in most cases) for dateutil parsing may be useful?

• https://github.com/pydata/pandas/blob/master/pandas/tslib.pyx#L1800

[jorisvandenbossche]

Another related case (also no (full) date part provided in the string) from #16074

In [20]: pd.to_datetime("4pm")
...
OutOfBoundsDatetime: Out of bounds nanosecond timestamp: 1-01-01 16:00:00

In [21]: pd.to_datetime("16:00")
Out[21]: Timestamp('2017-04-21 16:00:00')

so depending on the format of the time string, this does or does not work, so there is at least some inconsistency.

But I think we mainly have to decide on whether, if a part of the date (eg the year) or the full date is missing, do we fill it with 0001-01-01 (and with result that it raises an error) or with the current date?
In the first case, it is probably better to raise a custom error message instead of the OutOfBounds error.