DEPR: secondary_y plotting with implicit resample

Author: jbrockmendel

pandas/plotting/_matplotlib/timeseries.py

@@ -21,6 +21,8 @@
     OFFSET_TO_PERIOD_FREQSTR,
     FreqGroup,
 )
+from pandas.errors import Pandas4Warning
+from pandas.util._exceptions import find_stack_level
 
 from pandas.core.dtypes.generic import (
     ABCDatetimeIndex,
@@ -77,6 +79,13 @@ def maybe_resample(series: Series, ax: Axes, kwargs: dict[str, Any]):
         series = series.to_period(freq=freq)
 
     if ax_freq is not None and freq != ax_freq:
+        warnings.warn(
+            "Plotting with mixed-frequency series is deprecated and "
+            "will raise in a future version. Align series frequencies "
+            "before plotting instead.",
+            Pandas4Warning,
+            stacklevel=find_stack_level(),
+        )
         if is_superperiod(freq, ax_freq):  # upsample input
             series = series.copy()
             # error: "Index" has no attribute "asfreq"

pandas/tests/plotting/test_datetimelike.py

@@ -15,6 +15,7 @@
     BaseOffset,
     to_offset,
 )
+from pandas.errors import Pandas4Warning
 
 from pandas.core.dtypes.dtypes import PeriodDtype
 
@@ -627,7 +628,10 @@ def test_gap_upsample(self):
 
         idxh = date_range(low.index[0], low.index[-1], freq="12h")
         s = Series(np.random.default_rng(2).standard_normal(len(idxh)), idxh)
-        s.plot(secondary_y=True)
+
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            s.plot(secondary_y=True)
         lines = ax.get_lines()
         assert len(lines) == 1
         assert len(ax.right_ax.get_lines()) == 1
@@ -820,7 +824,9 @@ def test_mixed_freq_hf_first(self):
         low = Series(np.random.default_rng(2).standard_normal(len(idxl)), idxl)
         _, ax = mpl.pyplot.subplots()
         high.plot(ax=ax)
-        low.plot(ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            low.plot(ax=ax)
         for line in ax.get_lines():
             assert PeriodIndex(data=line.get_xdata()).freq == "D"
 
@@ -833,7 +839,9 @@ def test_mixed_freq_alignment(self):
 
         _, ax = mpl.pyplot.subplots()
         ax = ts.plot(ax=ax)
-        ts2.plot(style="r", ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            ts2.plot(style="r", ax=ax)
 
         assert ax.lines[0].get_xdata()[0] == ax.lines[1].get_xdata()[0]
 
@@ -844,7 +852,9 @@ def test_mixed_freq_lf_first(self):
         low = Series(np.random.default_rng(2).standard_normal(len(idxl)), idxl)
         _, ax = mpl.pyplot.subplots()
         low.plot(legend=True, ax=ax)
-        high.plot(legend=True, ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            high.plot(legend=True, ax=ax)
         for line in ax.get_lines():
             assert PeriodIndex(data=line.get_xdata()).freq == "D"
         leg = ax.get_legend()
@@ -858,7 +868,9 @@ def test_mixed_freq_lf_first_hourly(self):
         low = Series(np.random.default_rng(2).standard_normal(len(idxl)), idxl)
         _, ax = mpl.pyplot.subplots()
         low.plot(ax=ax)
-        high.plot(ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            high.plot(ax=ax)
         for line in ax.get_lines():
             assert PeriodIndex(data=line.get_xdata()).freq == "min"
 
@@ -951,7 +963,9 @@ def test_to_weekly_resampling(self):
         low = Series(np.random.default_rng(2).standard_normal(len(idxl)), idxl)
         _, ax = mpl.pyplot.subplots()
         high.plot(ax=ax)
-        low.plot(ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            low.plot(ax=ax)
         for line in ax.get_lines():
             assert PeriodIndex(data=line.get_xdata()).freq == idxh.freq
 
@@ -962,7 +976,9 @@ def test_from_weekly_resampling(self):
         low = Series(np.random.default_rng(2).standard_normal(len(idxl)), idxl)
         _, ax = mpl.pyplot.subplots()
         low.plot(ax=ax)
-        high.plot(ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            high.plot(ax=ax)
 
         expected_h = idxh.to_period().asi8.astype(np.float64)
         expected_l = np.array(
@@ -994,7 +1010,9 @@ def test_from_resampling_area_line_mixed(self, kind1, kind2):
 
         _, ax = mpl.pyplot.subplots()
         low.plot(kind=kind1, stacked=True, ax=ax)
-        high.plot(kind=kind2, stacked=True, ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            high.plot(kind=kind2, stacked=True, ax=ax)
 
         # check low dataframe result
         expected_x = np.array(
@@ -1049,7 +1067,9 @@ def test_from_resampling_area_line_mixed_high_to_low(self, kind1, kind2):
         )
         _, ax = mpl.pyplot.subplots()
         high.plot(kind=kind1, stacked=True, ax=ax)
-        low.plot(kind=kind2, stacked=True, ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            low.plot(kind=kind2, stacked=True, ax=ax)
 
         # check high dataframe result
         expected_x = idxh.to_period().asi8.astype(np.float64)
@@ -1096,7 +1116,9 @@ def test_mixed_freq_second_millisecond(self):
         # high to low
         _, ax = mpl.pyplot.subplots()
         high.plot(ax=ax)
-        low.plot(ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            low.plot(ax=ax)
         assert len(ax.get_lines()) == 2
         for line in ax.get_lines():
             assert PeriodIndex(data=line.get_xdata()).freq == "ms"
@@ -1110,7 +1132,9 @@ def test_mixed_freq_second_millisecond_low_to_high(self):
         # low to high
         _, ax = mpl.pyplot.subplots()
         low.plot(ax=ax)
-        high.plot(ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            high.plot(ax=ax)
         assert len(ax.get_lines()) == 2
         for line in ax.get_lines():
             assert PeriodIndex(data=line.get_xdata()).freq == "ms"
@@ -1247,7 +1271,9 @@ def test_secondary_upsample(self):
         low = Series(np.random.default_rng(2).standard_normal(len(idxl)), idxl)
         _, ax = mpl.pyplot.subplots()
         low.plot(ax=ax)
-        ax = high.plot(secondary_y=True, ax=ax)
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            ax = high.plot(secondary_y=True, ax=ax)
         for line in ax.get_lines():
             assert PeriodIndex(line.get_xdata()).freq == "D"
         assert hasattr(ax, "left_ax")
@@ -1482,7 +1508,11 @@ def test_secondary_y_mixed_freq_ts_xlim(self):
         _, ax = mpl.pyplot.subplots()
         ts.plot(ax=ax)
         left_before, right_before = ax.get_xlim()
-        ts.resample("D").mean().plot(secondary_y=True, ax=ax)
+
+        rs = ts.resample("D").mean()
+        msg = "Plotting with mixed-frequency series is deprecated"
+        with tm.assert_produces_warning(Pandas4Warning, match=msg):
+            rs.plot(secondary_y=True, ax=ax)
         left_after, right_after = ax.get_xlim()
 
         # a downsample should not have changed either limit