use f-string

Author: ganevgv

pandas/tests/window/test_timeseries_window.py

@@ -558,12 +558,12 @@ def test_ragged_max(self):
     def test_freqs_ops(self, freq, op, result_data):
         # GH 21096
         index = date_range(
-            start="2018-1-1 01:00:00", freq="1{}".format(freq), periods=10
+            start="2018-1-1 01:00:00", freq=f"1{freq}", periods=10
         )
         s = Series(data=0, index=index)
         s.iloc[1] = np.nan
         s.iloc[-1] = 2
-        result = getattr(s.rolling(window="10{}".format(freq)), op)()
+        result = getattr(s.rolling(window=f"10{freq}"), op)()
         expected = Series(data=result_data, index=index)
 
         tm.assert_series_equal(result, expected)