Fixed PolarAxes not using fmt_xdata and added simple test (matplotlib#4568) (matplotlib#28306)

* Fixed PolarAxes not using fmt_xdata and added simple test (matplotlib#4568)

Author: decxxx

lib/matplotlib/projections/polar.py

@@ -1447,12 +1447,25 @@ def format_sig(value, delta, opt, fmt):
                     cbook._g_sig_digits(value, delta))
             return f"{value:-{opt}.{prec}{fmt}}"
 
-        return ('\N{GREEK SMALL LETTER THETA}={}\N{GREEK SMALL LETTER PI} '
-                '({}\N{DEGREE SIGN}), r={}').format(
+        # In case fmt_xdata was not specified, resort to default
+
+        if self.fmt_ydata is None:
+            r_label = format_sig(r, delta_r, "#", "g")
+        else:
+            r_label = self.format_ydata(r)
+
+        if self.fmt_xdata is None:
+            return ('\N{GREEK SMALL LETTER THETA}={}\N{GREEK SMALL LETTER PI} '
+                    '({}\N{DEGREE SIGN}), r={}').format(
                     format_sig(theta_halfturns, delta_t_halfturns, "", "f"),
                     format_sig(theta_degrees, delta_t_degrees, "", "f"),
-                    format_sig(r, delta_r, "#", "g"),
+                    r_label
                 )
+        else:
+            return '\N{GREEK SMALL LETTER THETA}={}, r={}'.format(
+                        self.format_xdata(theta),
+                        r_label
+                        )
 
     def get_data_ratio(self):
         """

lib/matplotlib/tests/test_polar.py

@@ -436,6 +436,33 @@ def test_cursor_precision():
     assert ax.format_coord(2, 1) == "θ=0.637π (114.6°), r=1.000"
 
 
+def test_custom_fmt_data():
+    ax = plt.subplot(projection="polar")
+    def millions(x):
+        return '$%1.1fM' % (x*1e-6)
+
+    # Test only x formatter
+    ax.fmt_xdata = None
+    ax.fmt_ydata = millions
+    assert ax.format_coord(12, 2e7) == "θ=3.8197186342π (687.54935416°), r=$20.0M"
+    assert ax.format_coord(1234, 2e6) == "θ=392.794399551π (70702.9919191°), r=$2.0M"
+    assert ax.format_coord(3, 100) == "θ=0.95493π (171.887°), r=$0.0M"
+
+    # Test only y formatter
+    ax.fmt_xdata = millions
+    ax.fmt_ydata = None
+    assert ax.format_coord(2e5, 1) == "θ=$0.2M, r=1.000"
+    assert ax.format_coord(1, .1) == "θ=$0.0M, r=0.100"
+    assert ax.format_coord(1e6, 0.005) == "θ=$1.0M, r=0.005"
+
+    # Test both x and y formatters
+    ax.fmt_xdata = millions
+    ax.fmt_ydata = millions
+    assert ax.format_coord(2e6, 2e4*3e5) == "θ=$2.0M, r=$6000.0M"
+    assert ax.format_coord(1e18, 12891328123) == "θ=$1000000000000.0M, r=$12891.3M"
+    assert ax.format_coord(63**7, 1081968*1024) == "θ=$3938980.6M, r=$1107.9M"
+
+
 @image_comparison(['polar_log.png'], style='default')
 def test_polar_log():
     fig = plt.figure()