From 20e196027a7af60caa08e0d92f38cb63cc4c597e Mon Sep 17 00:00:00 2001
From: MarcoGorelli <>
Date: Thu, 6 Oct 2022 12:26:33 +0100
Subject: [PATCH 1/2] BUG: to_datetime(..., infer_datetime_format=True) fails
 with np.str_ input

---
 pandas/_libs/tslibs/parsing.pyx        | 4 ----
 pandas/core/tools/datetimes.py         | 8 +++++---
 pandas/tests/tools/test_to_datetime.py | 8 +++++---
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/pandas/_libs/tslibs/parsing.pyx b/pandas/_libs/tslibs/parsing.pyx
index 763530520cd29..51bb21404e7b5 100644
--- a/pandas/_libs/tslibs/parsing.pyx
+++ b/pandas/_libs/tslibs/parsing.pyx
@@ -963,10 +963,6 @@ def guess_datetime_format(dt_str: str, bint dayfirst=False) -> str | None:
         datetime format string (for `strftime` or `strptime`),
         or None if it can't be guessed.
     """
-
-    if not isinstance(dt_str, str):
-        return None
-
     day_attribute_and_format = (('day',), '%d', 2)
 
     # attr name, format, padding (if any)
diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index f9497860c00ba..204a2a0164c76 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -125,11 +125,13 @@ class FulldatetimeDict(YearMonthDayDict, total=False):
 # ---------------------------------------------------------------------
 
 
-def _guess_datetime_format_for_array(arr, dayfirst: bool | None = False):
-    # Try to guess the format based on the first non-NaN element
+def _guess_datetime_format_for_array(arr, dayfirst: bool | None = False) -> str | None:
+    # Try to guess the format based on the first non-NaN element, return None if can't
     non_nan_elements = notna(arr).nonzero()[0]
     if len(non_nan_elements):
-        return guess_datetime_format(arr[non_nan_elements[0]], dayfirst=dayfirst)
+        if type(first_non_nan_element := arr[non_nan_elements[0]]) is str:
+            # GH#32264 np.str_ object
+            return guess_datetime_format(first_non_nan_element, dayfirst=dayfirst)
 
 
 def should_cache(
diff --git a/pandas/tests/tools/test_to_datetime.py b/pandas/tests/tools/test_to_datetime.py
index 5c6b4c2434b88..3d59e115d4cf9 100644
--- a/pandas/tests/tools/test_to_datetime.py
+++ b/pandas/tests/tools/test_to_datetime.py
@@ -468,8 +468,10 @@ def test_to_datetime_mixed_datetime_and_string(self):
         expected = to_datetime([d1, d2]).tz_convert(pytz.FixedOffset(-60))
         tm.assert_index_equal(res, expected)
 
-    def test_to_datetime_np_str(self):
+    @pytest.mark.parametrize("infer_datetime_format", [True, False])
+    def test_to_datetime_np_str(self, infer_datetime_format):
         # GH#32264
+        # GH#48969
         value = np.str_("2019-02-04 10:18:46.297000+0000")
 
         ser = Series([value])
@@ -479,11 +481,11 @@ def test_to_datetime_np_str(self):
         assert to_datetime(value) == exp
         assert to_datetime(ser.iloc[0]) == exp
 
-        res = to_datetime([value])
+        res = to_datetime([value], infer_datetime_format=infer_datetime_format)
         expected = Index([exp])
         tm.assert_index_equal(res, expected)
 
-        res = to_datetime(ser)
+        res = to_datetime(ser, infer_datetime_format=infer_datetime_format)
         expected = Series(expected)
         tm.assert_series_equal(res, expected)
 

From 8dcb4fd74bc222b49ad2d8a2fc34cad69ac4c025 Mon Sep 17 00:00:00 2001
From: MarcoGorelli <>
Date: Thu, 6 Oct 2022 13:09:04 +0100
Subject: [PATCH 2/2] add return

---
 pandas/core/tools/datetimes.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index 204a2a0164c76..fe14f8e9907d6 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -132,6 +132,7 @@ def _guess_datetime_format_for_array(arr, dayfirst: bool | None = False) -> str
         if type(first_non_nan_element := arr[non_nan_elements[0]]) is str:
             # GH#32264 np.str_ object
             return guess_datetime_format(first_non_nan_element, dayfirst=dayfirst)
+    return None
 
 
 def should_cache(