Throw ValueError when irregularly gridded data is passed to streamplot.

anntzer · anntzer · commit bd643bdaad13 · 2018-10-10T15:24:21.000+02:00
... instead of silently generating an incorrect streamplot.
diff --git a/doc/api/api_changes/2018-10-10-AL.rst b/doc/api/api_changes/2018-10-10-AL.rst
@@ -0,0 +1,9 @@
+`Axes.streamplot` now raises ValueError when an irregular grid is passed in
+```````````````````````````````````````````````````````````````````````````
+
+`Axes.streamplot` does not support irregularly gridded ``x`` and ``y`` values.
+So far, it used to silently plot an incorrect result.  This has been changed to
+raise a ValueError instead.
+
+The `.streamplot.Grid` class, which is internally used by streamplot code, also
+throws a ValueError when irregularly gridded values are passed in.
diff --git a/lib/matplotlib/streamplot.py b/lib/matplotlib/streamplot.py
@@ -335,6 +335,11 @@ def __init__(self, x, y):
         self.width = x[-1] - x[0]
         self.height = y[-1] - y[0]
 
+        if not np.allclose(np.diff(x), self.width / (self.nx - 1)):
+            raise ValueError("'x' values must be equally spaced")
+        if not np.allclose(np.diff(y), self.height / (self.ny - 1)):
+            raise ValueError("'y' values must be equally spaced")
+
     @property
     def shape(self):
         return self.ny, self.nx
