Ensure polar plot radial lower limit remains at 0 after set_rticks + plot (matplotlib#29798)

Fix matplotlib#29528 set_rticks makes autoscale move the origin away from zero

Co-authored-by: Tim Hoffmann <[email protected]>
Co-authored-by: Ruth Comer <[email protected]>

Author: 3 people

lib/matplotlib/projections/polar.py

@@ -1292,7 +1292,10 @@ def set_rscale(self, *args, **kwargs):
         return Axes.set_yscale(self, *args, **kwargs)
 
     def set_rticks(self, *args, **kwargs):
-        return Axes.set_yticks(self, *args, **kwargs)
+        result = Axes.set_yticks(self, *args, **kwargs)
+        self.yaxis.set_major_locator(
+            self.RadialLocator(self.yaxis.get_major_locator(), self))
+        return result
 
     def set_thetagrids(self, angles, labels=None, fmt=None, **kwargs):
         """

lib/matplotlib/tests/test_polar.py

@@ -506,3 +506,23 @@ def test_polar_errorbar(order):
         ax.errorbar(theta, r, xerr=0.1, yerr=0.1, capsize=7, fmt="o", c="seagreen")
         ax.set_theta_zero_location("N")
         ax.set_theta_direction(-1)
+
+
+def test_radial_limits_behavior():
+    # r=0 is kept as limit if positive data and ticks are used
+    # negative ticks or data result in negative limits
+    fig = plt.figure()
+    ax = fig.add_subplot(projection='polar')
+    assert ax.get_ylim() == (0, 1)
+    # upper limit is expanded to include the ticks, but lower limit stays at 0
+    ax.set_rticks([1, 2, 3, 4])
+    assert ax.get_ylim() == (0, 4)
+    # upper limit is autoscaled to data, but lower limit limit stays 0
+    ax.plot([1, 2], [1, 2])
+    assert ax.get_ylim() == (0, 2)
+    # negative ticks also expand the negative limit
+    ax.set_rticks([-1, 0, 1, 2])
+    assert ax.get_ylim() == (-1, 2)
+    # negative data also autoscales to negative limits
+    ax.plot([1, 2], [-1, -2])
+    assert ax.get_ylim() == (-2, 2)