BUG: warning shown when parsing delimited date string even if users can't do anything about it (#50232)

* Revert "Inconsistent date parsing of to_datetime (#42908)"

This reverts commit 36e4165.

* post-merge fixup

* add test

* whatsnew

Co-authored-by: MarcoGorelli <>

Author: MarcoGorelli

doc/source/whatsnew/v2.0.0.rst

@@ -775,6 +775,7 @@ Datetimelike
 - Bug in ``pandas.tseries.holiday.Holiday`` where a half-open date interval causes inconsistent return types from :meth:`USFederalHolidayCalendar.holidays` (:issue:`49075`)
 - Bug in rendering :class:`DatetimeIndex` and :class:`Series` and :class:`DataFrame` with timezone-aware dtypes with ``dateutil`` or ``zoneinfo`` timezones near daylight-savings transitions (:issue:`49684`)
 - Bug in :func:`to_datetime` was raising ``ValueError`` when parsing :class:`Timestamp`, ``datetime.datetime``, ``datetime.date``, or ``np.datetime64`` objects when non-ISO8601 ``format`` was passed (:issue:`49298`, :issue:`50036`)
+- Bug in :class:`Timestamp` was showing ``UserWarning`` which was not actionable by users (:issue:`50232`)
 -
 
 Timedelta

pandas/_libs/tslibs/parsing.pyx

@@ -85,12 +85,6 @@ class DateParseError(ValueError):
 _DEFAULT_DATETIME = datetime(1, 1, 1).replace(hour=0, minute=0,
                                               second=0, microsecond=0)
 
-PARSING_WARNING_MSG = (
-    "Parsing dates in {format} format when dayfirst={dayfirst} was specified. "
-    "This may lead to inconsistently parsed dates! Specify a format "
-    "to ensure consistent parsing."
-)
-
 cdef:
     set _not_datelike_strings = {"a", "A", "m", "M", "p", "P", "t", "T"}
 
@@ -203,28 +197,10 @@ cdef object _parse_delimited_date(str date_string, bint dayfirst):
         # date_string can't be converted to date, above format
         return None, None
 
-    swapped_day_and_month = False
     if 1 <= month <= MAX_DAYS_IN_MONTH and 1 <= day <= MAX_DAYS_IN_MONTH \
             and (month <= MAX_MONTH or day <= MAX_MONTH):
         if (month > MAX_MONTH or (day <= MAX_MONTH and dayfirst)) and can_swap:
             day, month = month, day
-            swapped_day_and_month = True
-        if dayfirst and not swapped_day_and_month:
-            warnings.warn(
-                PARSING_WARNING_MSG.format(
-                    format="MM/DD/YYYY",
-                    dayfirst="True",
-                ),
-                stacklevel=find_stack_level(),
-            )
-        elif not dayfirst and swapped_day_and_month:
-            warnings.warn(
-                PARSING_WARNING_MSG.format(
-                    format="DD/MM/YYYY",
-                    dayfirst="False (the default)",
-                ),
-                stacklevel=find_stack_level(),
-            )
         # In Python <= 3.6.0 there is no range checking for invalid dates
         # in C api, thus we call faster C version for 3.6.1 or newer
         return datetime_new(year, month, day, 0, 0, 0, 0, None), reso

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -1082,3 +1082,11 @@ def test_as_unit_non_nano(self):
             == res.nanosecond
             == 0
         )
+
+
+def test_delimited_date():
+    # https://github.com/pandas-dev/pandas/issues/50231
+    with tm.assert_produces_warning(None):
+        result = Timestamp("13-01-2000")
+    expected = Timestamp(2000, 1, 13)
+    assert result == expected