Merge pull request matplotlib#21558 from anntzer/sp

Various small fixes for streamplot().

Author: timhoffm

lib/matplotlib/streamplot.py

@@ -116,8 +116,8 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
     if use_multicolor_lines:
         if color.shape != grid.shape:
             raise ValueError("If 'color' is given, it must match the shape of "
-                             "'Grid(x, y)'")
-        line_colors = []
+                             "the (x, y) grid")
+        line_colors = [[]]  # Empty entry allows concatenation of zero arrays.
         color = np.ma.masked_invalid(color)
     else:
         line_kw['color'] = color
@@ -126,7 +126,7 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
     if isinstance(linewidth, np.ndarray):
         if linewidth.shape != grid.shape:
             raise ValueError("If 'linewidth' is given, it must match the "
-                             "shape of 'Grid(x, y)'")
+                             "shape of the (x, y) grid")
         line_kw['linewidth'] = []
     else:
         line_kw['linewidth'] = linewidth
@@ -137,7 +137,7 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
 
     # Sanity checks.
     if u.shape != grid.shape or v.shape != grid.shape:
-        raise ValueError("'u' and 'v' must match the shape of 'Grid(x, y)'")
+        raise ValueError("'u' and 'v' must match the shape of the (x, y) grid")
 
     u = np.ma.masked_invalid(u)
     v = np.ma.masked_invalid(v)
@@ -310,21 +310,22 @@ class Grid:
     """Grid of data."""
     def __init__(self, x, y):
 
-        if x.ndim == 1:
+        if np.ndim(x) == 1:
             pass
-        elif x.ndim == 2:
-            x_row = x[0, :]
+        elif np.ndim(x) == 2:
+            x_row = x[0]
             if not np.allclose(x_row, x):
                 raise ValueError("The rows of 'x' must be equal")
             x = x_row
         else:
             raise ValueError("'x' can have at maximum 2 dimensions")
 
-        if y.ndim == 1:
+        if np.ndim(y) == 1:
             pass
-        elif y.ndim == 2:
-            y_col = y[:, 0]
-            if not np.allclose(y_col, y.T):
+        elif np.ndim(y) == 2:
+            yt = np.transpose(y)  # Also works for nested lists.
+            y_col = yt[0]
+            if not np.allclose(y_col, yt):
                 raise ValueError("The columns of 'y' must be equal")
             y = y_col
         else:

lib/matplotlib/tests/test_streamplot.py

@@ -144,3 +144,13 @@ def test_streamplot_grid():
 
     with pytest.raises(ValueError, match="'y' must be strictly increasing"):
         plt.streamplot(x, y, u, v)
+
+
+def test_streamplot_inputs():  # test no exception occurs.
+    # fully-masked
+    plt.streamplot(np.arange(3), np.arange(3),
+                   np.full((3, 3), np.nan), np.full((3, 3), np.nan),
+                   color=np.random.rand(3, 3))
+    # array-likes
+    plt.streamplot(range(3), range(3),
+                   np.random.rand(3, 3), np.random.rand(3, 3))