From 02033d45b681d602f18b2c01b7429356e18e7186 Mon Sep 17 00:00:00 2001
From: MarcoGorelli <>
Date: Sun, 16 Oct 2022 09:38:02 +0100
Subject: [PATCH 1/2] guess %Y format

---
 pandas/_libs/tslibs/parsing.pyx     | 8 ++++++--
 pandas/tests/tslibs/test_parsing.py | 1 +
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/pandas/_libs/tslibs/parsing.pyx b/pandas/_libs/tslibs/parsing.pyx
index e0fcc829ad326..5c93edfee79f2 100644
--- a/pandas/_libs/tslibs/parsing.pyx
+++ b/pandas/_libs/tslibs/parsing.pyx
@@ -1053,8 +1053,12 @@ def guess_datetime_format(dt_str: str, bint dayfirst=False) -> str | None:
                 found_attrs.update(attrs)
                 break
 
-    # Only consider it a valid guess if we have a year, month and day
-    if len({'year', 'month', 'day'} & found_attrs) != 3:
+    # Only consider it a valid guess if we have a year, month and day,
+    # unless it's %Y which is both common and unambiguous.
+    if (
+        len({'year', 'month', 'day'} & found_attrs) != 3
+        and format_guess != ['%Y']
+    ):
         return None
 
     output_format = []
diff --git a/pandas/tests/tslibs/test_parsing.py b/pandas/tests/tslibs/test_parsing.py
index 9588f54388d1e..642162cb8a864 100644
--- a/pandas/tests/tslibs/test_parsing.py
+++ b/pandas/tests/tslibs/test_parsing.py
@@ -147,6 +147,7 @@ def test_parsers_month_freq(date_str, expected):
     [
         ("20111230", "%Y%m%d"),
         ("2011-12-30", "%Y-%m-%d"),
+        ("2011", "%Y"),
         ("30-12-2011", "%d-%m-%Y"),
         ("2011-12-30 00:00:00", "%Y-%m-%d %H:%M:%S"),
         ("2011-12-30T00:00:00", "%Y-%m-%dT%H:%M:%S"),

From 5b50d8c559d2b103209f9871d7fe0168baab28f6 Mon Sep 17 00:00:00 2001
From: MarcoGorelli <>
Date: Sun, 16 Oct 2022 09:55:10 +0100
Subject: [PATCH 2/2] fixup

---
 pandas/tests/tslibs/test_parsing.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/tests/tslibs/test_parsing.py b/pandas/tests/tslibs/test_parsing.py
index 642162cb8a864..fcfca5a27763b 100644
--- a/pandas/tests/tslibs/test_parsing.py
+++ b/pandas/tests/tslibs/test_parsing.py
@@ -209,7 +209,6 @@ def test_guess_datetime_format_with_locale_specific_formats(string, fmt):
 @pytest.mark.parametrize(
     "invalid_dt",
     [
-        "2013",
         "01/2013",
         "12:00:00",
         "1/1/1/1",