New Timestamp.fast_strftime, leveraged by format_array_from_datetime. Fixes issue related to timezone-aware timestamp formatting. Added corresponding tests.

Author: Sylvain MARIE

pandas/_libs/tslib.pyx

@@ -199,14 +199,19 @@ def format_array_from_datetime(
 
         elif fast_strftime:
 
-            dt64_to_dtstruct(val, &dts)
-
-            # Use string formatting for faster strftime
-            result[i] = str_format % dict(
-                year=dts.year, month=dts.month, day=dts.day, hour=dts.hour,
-                min=dts.min, sec=dts.sec, us=dts.us
-            )
+            if tz is None:
+                dt64_to_dtstruct(val, &dts)
+
+                # Use string formatting for faster strftime
+                result[i] = str_format % dict(
+                    year=dts.year, month=dts.month, day=dts.day, hour=dts.hour,
+                    min=dts.min, sec=dts.sec, us=dts.us
+                )
+            else:
+                ts = Timestamp(val, tz=tz)
 
+                # Use string formatting for faster strftime
+                result[i] = ts.fast_strftime(str_format)
         else:
 
             ts = Timestamp(val, tz=tz)

pandas/_libs/tslibs/timestamps.pyx

@@ -1195,6 +1195,25 @@ class Timestamp(_Timestamp):
         tz = maybe_get_tz(tz)
         return cls(datetime.fromtimestamp(ts, tz))
 
+    def fast_strftime(self, fmt_str: str) -> str:
+        """A faster alternative to `strftime` using string formatting.
+
+        `fmt_str` should be created using `convert_strftime_format(fmt)`.
+
+        See also `self.strftime`, that relies on `datetime.strftime`.
+
+        Examples
+        --------
+        >>> ts = pd.Timestamp('2020-03-14T15:32:52.192548651')
+        >>> fmt = convert_strftime_format('%Y-%m-%d %X')
+        >>> ts.fast_strftime(fmt)
+        '2020-03-14 15:32:52'
+        """
+        return fmt_str % dict(
+            year=self.year, month=self.month, day=self.day, hour=self.hour,
+            min=self.minute, sec=self.second, us=self.microsecond
+        )
+
     def strftime(self, format):
         """
         Timestamp.strftime(format)

pandas/tests/io/formats/test_format.py

@@ -3175,6 +3175,24 @@ def test_datetime(self):
         assert formatted[0] == "2003-01-01 12:00:00"
         assert formatted[1] == "NaT"
 
+    def test_datetime_tz(self):
+        # This timestamp is in 2013 in Europe/Paris but is 2012 in UTC
+        dt = pd.to_datetime(["2013-01-01 00:00:00+01:00"], utc=True)
+        # If tz is currently set as utc, we'll see 2012
+        assert dt.format()[0] == "2012-12-31 23:00:00+00:00"
+        # If tz is currently set as paris, we'll see 2013
+        dt = dt.tz_convert("Europe/Paris")
+        assert dt.format()[0] == "2013-01-01 00:00:00+01:00"
+
+    def test_datetime_tz_custom(self):
+        # This timestamp is in 2013 in Europe/Paris but is 2012 in UTC
+        dt = pd.to_datetime(["2013-01-01 00:00:00+01:00"], utc=True)
+        # If tz is currently set as utc, we'll see 2012
+        assert dt.format(date_format="%Y-%m-%d__foo__%H:%M:%S")[0] == "2012-12-31__foo__23:00:00"
+        # If tz is currently set as paris, we'll see 2013
+        dt = dt.tz_convert("Europe/Paris")
+        assert dt.format(date_format="%Y-%m-%d__foo__%H:%M:%S")[0] == "2013-01-01__foo__00:00:00"
+
     def test_date(self):
         formatted = pd.to_datetime([datetime(2003, 1, 1), NaT]).format()
         assert formatted[0] == "2003-01-01"