fixed bug with legend of plot_vector

spb/backends/base_backend.py

@@ -334,8 +334,11 @@ def __init__(self, *args, **kwargs):
         self.legend = kwargs.get("legend", None)
         if self.legend is None:
             series_to_show = [
-                s for s in self._series if (s.show_in_legend and (not s.use_cm)
-                and (not s.is_grid))
+                s for s in self._series if (
+                    s.show_in_legend and
+                    (not s.use_cm) and
+                    (not s.is_grid)
+                )
             ]
             if len(series_to_show) > 1:
                 # don't show the legend if `plot_piecewise` created this

spb/series.py

@@ -2178,6 +2178,7 @@ def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.is_filled = kwargs.get("is_filled", kwargs.get("fill", True))
         self.show_clabels = kwargs.get("clabels", True)
+        self.use_cm = True
 
         # NOTE: contour plots are used by plot_contour, plot_vector and
         # plot_complex_vector. By implementing contour_kw we are able to
@@ -2709,6 +2710,7 @@ def __init__(self, expr, r, label="", **kwargs):
         if not kwargs.get("threed", False):
             self.is_contour = True
             self.is_3Dsurface = False
+            self.use_cm = True
         self.is_filled = kwargs.get("is_filled", kwargs.get("fill", True))
         self.show_clabels = kwargs.get("clabels", True)
         self._post_init()

tests/backends/test_matplotlib.py

@@ -15,7 +15,10 @@
     plot_complex_list, graphics, vector_field_2d, plot_nyquist, plot_nichols,
     plot_step_response
 )
-from spb.series import RootLocusSeries, SGridLineSeries, ZGridLineSeries
+from spb.series import (
+    RootLocusSeries, SGridLineSeries, ZGridLineSeries, ContourSeries,
+    Vector2DSeries
+)
 from spb.series import SurfaceOver2DRangeSeries
 from sympy import (
     sin, cos, I, pi, Eq, exp, Circle, Polygon, sqrt, Matrix, Line, Segment,
@@ -2603,3 +2606,32 @@ def test_hvlines():
     )
     p.backend.update_interactive({a: 3, b: 4})
     p.backend.close()
+
+
+def test_plot_vector_2d_legend_1():
+    x, y = symbols("x, y")
+    p = plot_vector(
+        [-sin(y), cos(x)], (x, -pi, pi), (y, -pi, pi),
+        backend=MB, scalar=True, n=10, show=False
+    )
+    assert isinstance(p[0], ContourSeries)
+    assert isinstance(p[1], Vector2DSeries)
+    assert not p[1].use_cm
+    # this is because there is only one vector series with use_cm=False
+    assert p.legend is None
+
+@pytest.mark.parametrize(
+    "streamlines, use_cm, expected", [
+        (False, False, True),
+        (False, True, None),
+        (True, False, True),
+        (True, True, None)
+    ]
+)
+def test_plot_vector_2d_legend_2(streamlines, use_cm, expected):
+    x, y = symbols("x, y")
+    p = plot_vector(
+        [-sin(y), cos(x)], [cos(x), -sin(y)], (x, -pi, pi), (y, -pi, pi),
+        backend=MB, n=10, show=False, streamlines=streamlines, use_cm=use_cm
+    )
+    assert p.legend is expected

tests/test_series.py

@@ -1996,7 +1996,7 @@ def test_use_cm(use_cm):
         sqrt(z), (z, -2 - 3j, 4 + 5j),
         threed=False, use_cm=use_cm
     )
-    assert s.use_cm is use_cm
+    assert s.use_cm is True
 
     s = ComplexSurfaceSeries(
         sqrt(z), (z, -2 - 3j, 4 + 5j),