matplotlib
diff --git a/‎lib/matplotlib/collections.py
Lines changed: 13 additions & 5 deletions b/‎lib/matplotlib/collections.py
Lines changed: 13 additions & 5 deletions
diff --git a/‎lib/matplotlib/tests/test_collections.py
Lines changed: 10 additions & 0 deletions b/‎lib/matplotlib/tests/test_collections.py
Lines changed: 10 additions & 0 deletions
@@ -592,10 +592,7 @@ def get_offset_position(self):
 
     def _get_default_linewidth(self):
         # This may be overridden in a subclass.
-        lw = mpl.rcParams['patch.linewidth']
-        if lw is None:
-            lw = mpl.rcParams['lines.linewidth']
-        return lw
+        return mpl.rcParams['patch.linewidth']  # validated as float
 
     def set_linewidth(self, lw):
         """
@@ -1419,6 +1416,7 @@ class LineCollection(Collection):
     _edge_default = True
 
     def __init__(self, segments,  # Can be None.
+                 *args,           # Deprecated.
                  zorder=2,        # Collection.zorder is 1
                  **kwargs
                  ):
@@ -1453,7 +1451,17 @@ def __init__(self, segments,  # Can be None.
         **kwargs
             Forwarded to `.Collection`.
         """
-
+        argnames = ["linewidths", "colors", "antialiaseds", "linestyles",
+                    "offsets", "transOffset", "norm", "cmap", "pickradius",
+                    "zorder", "facecolors"]
+        if args:
+            argkw = {name: val for name, val in zip(argnames, args)}
+            kwargs.update(argkw)
+            cbook.warn_deprecated(
+                "3.4", message="In a future release, all LineCollection "
+                "arguments other than the first, 'segments', will be "
+                "keyword-only arguments."
+                )
         super().__init__(
             zorder=zorder,
             **kwargs)
 
@@ -12,6 +12,7 @@
 from matplotlib.collections import (Collection, LineCollection,
                                     EventCollection, PolyCollection)
 from matplotlib.testing.decorators import image_comparison
+from matplotlib.cbook.deprecation import MatplotlibDeprecationWarning
 
 
 def generate_EventCollection_plot():
@@ -789,6 +790,15 @@ def test_color_logic(pcfunc):
     assert_array_equal(pc.get_edgecolor(), [[1, 0, 0, 1]])
 
 
+def test_LineCollection_args():
+    with pytest.warns(MatplotlibDeprecationWarning):
+        lc = LineCollection(None, 2.2, 'r', zorder=3, facecolors=[0, 1, 0, 1])
+        assert lc.get_linewidth()[0] == 2.2
+        assert list(lc.get_edgecolor()[0]) == [1, 0, 0, 1]
+        assert lc.get_zorder() == 3
+        assert list(lc.get_facecolor()[0]) == [0, 1, 0, 1]
+
+
 def test_array_wrong_dimensions():
     z = np.arange(12).reshape(3, 4)
     pc = plt.pcolor(z)