Backport PR #17821: FIX: Keep lists of lists of one scalar each 2D in _reshape_2D

dstansby · meeseeksmachine · commit 57708cbdee7c · 2020-07-02T18:41:55.000Z
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -1363,12 +1363,12 @@ def _reshape_2D(X, name):
     result = []
     is_1d = True
     for xi in X:
+        if isinstance(xi, collections.abc.Iterable):
+            is_1d = False
         xi = np.asanyarray(xi)
         nd = np.ndim(xi)
         if nd > 1:
             raise ValueError(f'{name} must have 2 or fewer dimensions')
-        elif nd == 1 and len(xi) != 1:
-            is_1d = False
         result.append(xi.reshape(-1))
 
     if is_1d:
diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
@@ -502,6 +502,14 @@ class dummy:
     xnew = cbook._reshape_2D(x, 'x')
     assert np.shape(xnew) == (5, 3)
 
+    # Test a list of lists which are all of length 1
+    x = [[1], [2], [3]]
+    xnew = cbook._reshape_2D(x, 'x')
+    assert isinstance(xnew, list)
+    assert isinstance(xnew[0], np.ndarray) and xnew[0].shape == (1,)
+    assert isinstance(xnew[1], np.ndarray) and xnew[1].shape == (1,)
+    assert isinstance(xnew[2], np.ndarray) and xnew[2].shape == (1,)
+
     # Now test with a list of lists with different lengths, which means the
     # array will internally be converted to a 1D object array of lists
     x = [[1, 2, 3], [3, 4], [2]]
