BUG: fix hardcoded scatter marker size issue #54204

doc/source/getting_started/intro_tutorials/04_plotting.rst

@@ -103,7 +103,7 @@ I want to visually compare the :math:`NO_2` values measured in London versus Par
 .. ipython:: python
 
     @savefig 04_airqual_scatter.png
-    air_quality.plot.scatter(x="station_london", y="station_paris", alpha=0.5)
+    air_quality.plot.scatter(x="station_london", y="station_paris", s = 20, alpha=0.5)
     plt.show()
 
 .. raw:: html
@@ -117,11 +117,14 @@ standard Python to get an overview of the available plot methods:
 
 .. ipython:: python
 
-    [
-        method_name
-        for method_name in dir(air_quality.plot)
-        if not method_name.startswith("_")
-    ]
+    import warnings
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore")
+        [
+            method_name
+            for method_name in dir(air_quality.plot)
+            if not method_name.startswith("_")
+        ]
 
 .. note::
     In many development environments as well as IPython and

doc/source/user_guide/dsintro.rst

@@ -570,7 +570,7 @@ greater than 5, calculate the ratio, and plot:
            SepalRatio=lambda x: x.SepalWidth / x.SepalLength,
            PetalRatio=lambda x: x.PetalWidth / x.PetalLength,
        )
-       .plot(kind="scatter", x="SepalRatio", y="PetalRatio")
+       .plot(kind="scatter", x="SepalRatio", y="PetalRatio", s = 20)
    )
 
 Since a function is passed in, the function is computed on the DataFrame

doc/source/user_guide/visualization.rst

@@ -626,7 +626,7 @@ It is recommended to specify ``color`` and ``label`` keywords to distinguish eac
 
    ax = df.plot.scatter(x="a", y="b", color="DarkBlue", label="Group 1")
    @savefig scatter_plot_repeated.png
-   df.plot.scatter(x="c", y="d", color="DarkGreen", label="Group 2", ax=ax);
+   df.plot.scatter(x="c", y="d", color="DarkGreen", label="Group 2", ax=ax, s = 20);
 
 .. ipython:: python
    :suppress:

doc/source/whatsnew/v2.1.0.rst

@@ -605,7 +605,7 @@ Plotting
 ^^^^^^^^
 - Bug in :meth:`Series.plot` when invoked with ``color=None`` (:issue:`51953`)
 - Fixed UserWarning in :meth:`DataFrame.plot.scatter` when invoked with ``c="b"`` (:issue:`53908`)
--
+- Fixed bug in :meth:`DataFrame.plot.scatter` wherein marker size was previously hardcoded to a default value (:issue:`54204`)
 
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^

pandas/plotting/_matplotlib/core.py

@@ -1199,9 +1199,18 @@ def _kind(self) -> Literal["scatter"]:
 
     def __init__(self, data, x, y, s=None, c=None, **kwargs) -> None:
         if s is None:
-            # hide the matplotlib default for size, in case we want to change
-            # the handling of this argument later
-            s = 20
+            #  The default size of the elements in a scatter plot
+            # is now based on the rcParam ``lines.markersize``.
+            # This means that if rcParams are temporarily changed,
+            # the marker size changes as well according to mpl.rc_context().
+            warnings.warn(
+                """The default of s=20 is deprecated and
+                has changed to mpl.rcParams['lines.markersize'].
+                Specify `s` to suppress this warning""",
+                DeprecationWarning,
+                stacklevel=find_stack_level(),
+            )
+            s = mpl.rcParams["lines.markersize"] ** 2.0
         elif is_hashable(s) and s in data.columns:
             s = data[s]
         super().__init__(data, x, y, s=s, **kwargs)

pandas/tests/plotting/test_misc.py

@@ -662,3 +662,35 @@ def test_bar_plt_xaxis_intervalrange(self):
             (a.get_text() == b.get_text())
             for a, b in zip(s.plot.bar().get_xticklabels(), expected)
         )
+
+    @pytest.mark.filterwarnings("default")
+    def test_change_scatter_markersize_rcparams(self):
+        # GH 54204
+        # Ensure proper use of lines.markersize to style pandas scatter
+        # plots like matplotlib does.
+        # Will raise deprecation warnings.
+        df = DataFrame(data={"x": [1, 2, 3], "y": [1, 2, 3]})
+
+        pandas_default = df.plot.scatter(
+            x="x", y="y", title="pandas scatter, default rc marker size"
+        )
+
+        mpl_default = mpl.pyplot.scatter(df["x"], df["y"])
+
+        # verify that pandas and matplotlib scatter
+        # default marker size are the same (s = 6^2 = 36)
+        assert (
+            pandas_default.collections[0].get_sizes()[0] == mpl_default.get_sizes()[0]
+        )
+
+        with mpl.rc_context({"lines.markersize": 10}):
+            pandas_changed = df.plot.scatter(
+                x="x", y="y", title="pandas scatter, changed rc marker size"
+            )
+            mpl_changed = mpl.pyplot.scatter(df["x"], df["y"])
+
+        # verify that pandas and matplotlib scatter
+        # changed marker size are the same (s = 10^2 = 100)
+        assert (
+            pandas_changed.collections[0].get_sizes()[0] == mpl_changed.get_sizes()[0]
+        )