Fix bug that caused a crash when setting negative limits and using log scale

astrofrog · astrofrog · commit 3fc50c7c5210 · 2019-06-26T16:35:17.000+02:00
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3240,10 +3240,11 @@ def set_xlim(self, left=None, right=None, emit=True, auto=False,
         left = self._validate_converted_limits(left, self.convert_xunits)
         right = self._validate_converted_limits(right, self.convert_xunits)
 
+        old_left, old_right = self.get_xlim()
+
         if left is None or right is None:
             # Axes init calls set_xlim(0, 1) before get_xlim() can be called,
             # so only grab the limits if we really need them.
-            old_left, old_right = self.get_xlim()
             if left is None:
                 left = old_left
             if right is None:
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -2141,6 +2141,14 @@ def test_log_scales():
     ax.set_xscale('log', basex=9.0)
 
 
+def test_log_scales_invalid():
+    fig = plt.figure()
+    ax = fig.add_subplot(1, 1, 1)
+    ax.set_xscale('log')
+    with pytest.warns(UserWarning, match='Attempted to set non-positive'):
+        ax.set_xlim(-1, 10)
+
+
 @image_comparison(['stackplot_test_image', 'stackplot_test_image'])
 def test_stackplot():
     fig = plt.figure()
