matplotlib · efiring · Apr 15, 2015 · Apr 13, 2015 · Apr 13, 2015
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -1141,6 +1141,12 @@ def eventplot(self, positions, orientation='horizontal', lineoffsets=1,
         if len(positions) == 0:
             return []
 
+        # prevent 'singular' keys from **kwargs dict from overriding the effect
+        # of 'plural' keyword arguments (e.g. 'color' overriding 'colors')
+        colors = cbook.local_over_kwdict(colors, kwargs, 'color')
+        linewidths = cbook.local_over_kwdict(linewidths, kwargs, 'linewidth')
+        linestyles = cbook.local_over_kwdict(linestyles, kwargs, 'linestyle')
+
         if not iterable(lineoffsets):
             lineoffsets = [lineoffsets]
         if not iterable(linelengths):

diff --git a/lib/matplotlib/cbook.py b/lib/matplotlib/cbook.py
@@ -658,6 +658,62 @@ def __setstate__(self, state):
         self.extend(state['seq'])
 
 
+class IgnoredKeywordWarning(UserWarning):
+    """
+    A class for issuing warnings about keyword arguments that will be ignored
+    by matplotlib
+    """
+    pass
+
+
+def local_over_kwdict(local_var, kwargs, *keys):
+    """
+    Enforces the priority of a local variable over potentially conflicting
+    argument(s) from a kwargs dict. The following possible output values are
+    considered in order of priority:
+
+        local_var > kwargs[keys[0]] > ... > kwargs[keys[-1]]
+
+    The first of these whose value is not None will be returned. If all are
+    None then None will be returned. Each key in keys will be removed from the
+    kwargs dict in place.
+
+    Parameters
+    ------------
+        local_var: any object
+            The local variable (highest priority)
+
+        kwargs: dict
+            Dictionary of keyword arguments; modified in place
+
+        keys: str(s)
+            Name(s) of keyword arguments to process, in descending order of
+            priority
+
+    Returns
+    ---------
+        out: any object
+            Either local_var or one of kwargs[key] for key in keys
+
+    Raises
+    --------
+        IgnoredKeywordWarning
+            For each key in keys that is removed from kwargs but not used as
+            the output value
+
+    """
+    out = local_var
+    for key in keys:
+        kwarg_val = kwargs.pop(key, None)
+        if kwarg_val is not None:
+            if out is None:
+                out = kwarg_val
+            else:
+                warnings.warn('"%s" keyword argument will be ignored' % key,
+                              IgnoredKeywordWarning)
+    return out
+
+
 def strip_math(s):
     'remove latex formatting from mathtext'
     remove = (r'\mathdefault', r'\rm', r'\cal', r'\tt', r'\it', '\\', '{', '}')

diff --git a/lib/matplotlib/tests/baseline_images/test_axes/test_eventplot_problem_kwargs.png b/lib/matplotlib/tests/baseline_images/test_axes/test_eventplot_problem_kwargs.png
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -20,6 +20,7 @@
 import matplotlib.markers as mmarkers
 from numpy.testing import assert_array_equal
 import warnings
+from matplotlib.cbook import IgnoredKeywordWarning
 
 
 @image_comparison(baseline_images=['formatter_ticker_001',
@@ -2317,6 +2318,37 @@ def test_eventplot_defaults():
     colls = axobj.eventplot(data)
 
 
+@image_comparison(baseline_images=['test_eventplot_problem_kwargs'], extensions=['png'], remove_text=True)
+def test_eventplot_problem_kwargs():
+    '''
+    test that 'singular' versions of LineCollection props raise an
+    IgnoredKeywordWarning rather than overriding the 'plural' versions (e.g.
+    to prevent 'color' from overriding 'colors', see issue #4297)
+    '''
+    np.random.seed(0)
+
+    data1 = np.random.random([20]).tolist()
+    data2 = np.random.random([10]).tolist()
+    data = [data1, data2]
+
+    fig = plt.figure()
+    axobj = fig.add_subplot(111)
+
+    with warnings.catch_warnings(record=True) as w:
+        colls = axobj.eventplot(data,
+                                colors=['r', 'b'],
+                                color=['c', 'm'],
+                                linewidths=[2, 1],
+                                linewidth=[1, 2],
+                                linestyles=['solid', 'dashed'],
+                                linestyle=['dashdot', 'dotted'])
+
+        # check that three IgnoredKeywordWarnings were raised
+        assert_equal(len(w), 3)
+        assert_true(all(issubclass(wi.category, IgnoredKeywordWarning)
+                    for wi in w))
+
+
 @cleanup
 def test_empty_eventplot():
     fig, ax = plt.subplots(1, 1)