ENH: guess ISO8601 formats without separators (#50622)

expand guess_datetime_format a bit

Co-authored-by: MarcoGorelli <>

Author: MarcoGorelli

pandas/_libs/tslibs/parsing.pyx

@@ -848,7 +848,12 @@ def guess_datetime_format(dt_str: str, bint dayfirst=False) -> str | None:
 
     # attr name, format, padding (if any)
     datetime_attrs_to_format = [
+        (("year", "month", "day", "hour", "minute", "second"), "%Y%m%d%H%M%S", 0),
+        (("year", "month", "day", "hour", "minute"), "%Y%m%d%H%M", 0),
+        (("year", "month", "day", "hour"), "%Y%m%d%H", 0),
         (("year", "month", "day"), "%Y%m%d", 0),
+        (("hour", "minute", "second"), "%H%M%S", 0),
+        (("hour", "minute"), "%H%M", 0),
         (("year",), "%Y", 0),
         (("month",), "%B", 0),
         (("month",), "%b", 0),

pandas/tests/tools/test_to_datetime.py

@@ -2893,8 +2893,8 @@ class TestDatetimeParsingWrappers:
             ("2014-6", datetime(2014, 6, 1), None),
             ("6-2014", datetime(2014, 6, 1), UserWarning),
             ("20010101 12", datetime(2001, 1, 1, 12), None),
-            ("20010101 1234", datetime(2001, 1, 1, 12, 34), UserWarning),
-            ("20010101 123456", datetime(2001, 1, 1, 12, 34, 56), UserWarning),
+            ("20010101 1234", datetime(2001, 1, 1, 12, 34), None),
+            ("20010101 123456", datetime(2001, 1, 1, 12, 34, 56), None),
         ],
     )
     def test_parsers(self, date_str, expected, warning, cache):

pandas/tests/tslibs/test_parsing.py

@@ -149,6 +149,11 @@ def test_parsers_month_freq(date_str, expected):
     "string,fmt",
     [
         ("20111230", "%Y%m%d"),
+        ("201112300000", "%Y%m%d%H%M"),
+        ("20111230000000", "%Y%m%d%H%M%S"),
+        ("20111230T00", "%Y%m%dT%H"),
+        ("20111230T0000", "%Y%m%dT%H%M"),
+        ("20111230T000000", "%Y%m%dT%H%M%S"),
         ("2011-12-30", "%Y-%m-%d"),
         ("2011", "%Y"),
         ("2011-01", "%Y-%m"),