In [9]: plt.plot(x, x, mec=np.array([0.1, 0.1, 0.1]))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-9-d091fe25a343> in <module>()
----> 1 plt.plot(x, x, mec=np.array([0.1, 0.1, 0.1]))

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/pyplot.py in plot(*args, **kwargs)
   3315                       mplDeprecation)
   3316     try:
-> 3317         ret = ax.plot(*args, **kwargs)
   3318     finally:
   3319         ax._hold = washold

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/__init__.py in inner(ax, *args, **kwargs)
   1896                     warnings.warn(msg % (label_namer, func.__name__),
   1897                                   RuntimeWarning, stacklevel=2)
-> 1898             return func(ax, *args, **kwargs)
   1899         pre_doc = inner.__doc__
   1900         if pre_doc is None:

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_axes.py in plot(self, *args, **kwargs)
   1404         kwargs = cbook.normalize_kwargs(kwargs, _alias_map)
   1405 
-> 1406         for line in self._get_lines(*args, **kwargs):
   1407             self.add_line(line)
   1408             lines.append(line)

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_base.py in _grab_next_args(self, *args, **kwargs)
    405                 return
    406             if len(remaining) <= 3:
--> 407                 for seg in self._plot_args(remaining, kwargs):
    408                     yield seg
    409                 return

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_base.py in _plot_args(self, tup, kwargs)
    393         ncx, ncy = x.shape[1], y.shape[1]
    394         for j in xrange(max(ncx, ncy)):
--> 395             seg = func(x[:, j % ncx], y[:, j % ncy], kw, kwargs)
    396             ret.append(seg)
    397         return ret

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_base.py in _makeline(self, x, y, kw, kwargs)
    300         default_dict = self._getdefaults(None, kw)
    301         self._setdefaults(default_dict, kw)
--> 302         seg = mlines.Line2D(x, y, **kw)
    303         return seg
    304 

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/lines.py in __init__(self, xdata, ydata, linewidth, linestyle, color, marker, markersize, markeredgewidth, markeredgecolor, markerfacecolor, markerfacecoloralt, fillstyle, antialiased, dash_capstyle, solid_capstyle, dash_joinstyle, solid_joinstyle, pickradius, drawstyle, markevery, **kwargs)
    420         self.set_markerfacecolor(markerfacecolor)
    421         self.set_markerfacecoloralt(markerfacecoloralt)
--> 422         self.set_markeredgecolor(markeredgecolor)
    423         self.set_markeredgewidth(markeredgewidth)
    424 

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/lines.py in set_markeredgecolor(self, ec)
   1180         if ec is None:
   1181             ec = 'auto'
-> 1182         if self._markeredgecolor != ec:
   1183             self.stale = True
   1184         self._markeredgecolor = ec

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

In [10]: plt.plot(x, x, mec=[0.1, 0.1, 0.1])
Out[10]: [<matplotlib.lines.Line2D at 0x7f17949e84a8>]

In [11]: plt.plot(x, x, mec=np.array([0.1, 0.1, 0.1]))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-11-d091fe25a343> in <module>()
----> 1 plt.plot(x, x, mec=np.array([0.1, 0.1, 0.1]))

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/pyplot.py in plot(*args, **kwargs)
   3315                       mplDeprecation)
   3316     try:
-> 3317         ret = ax.plot(*args, **kwargs)
   3318     finally:
   3319         ax._hold = washold

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/__init__.py in inner(ax, *args, **kwargs)
   1896                     warnings.warn(msg % (label_namer, func.__name__),
   1897                                   RuntimeWarning, stacklevel=2)
-> 1898             return func(ax, *args, **kwargs)
   1899         pre_doc = inner.__doc__
   1900         if pre_doc is None:

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_axes.py in plot(self, *args, **kwargs)
   1404         kwargs = cbook.normalize_kwargs(kwargs, _alias_map)
   1405 
-> 1406         for line in self._get_lines(*args, **kwargs):
   1407             self.add_line(line)
   1408             lines.append(line)

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_base.py in _grab_next_args(self, *args, **kwargs)
    405                 return
    406             if len(remaining) <= 3:
--> 407                 for seg in self._plot_args(remaining, kwargs):
    408                     yield seg
    409                 return

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_base.py in _plot_args(self, tup, kwargs)
    393         ncx, ncy = x.shape[1], y.shape[1]
    394         for j in xrange(max(ncx, ncy)):
--> 395             seg = func(x[:, j % ncx], y[:, j % ncy], kw, kwargs)
    396             ret.append(seg)
    397         return ret

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/axes/_base.py in _makeline(self, x, y, kw, kwargs)
    300         default_dict = self._getdefaults(None, kw)
    301         self._setdefaults(default_dict, kw)
--> 302         seg = mlines.Line2D(x, y, **kw)
    303         return seg
    304 

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/lines.py in __init__(self, xdata, ydata, linewidth, linestyle, color, marker, markersize, markeredgewidth, markeredgecolor, markerfacecolor, markerfacecoloralt, fillstyle, antialiased, dash_capstyle, solid_capstyle, dash_joinstyle, solid_joinstyle, pickradius, drawstyle, markevery, **kwargs)
    420         self.set_markerfacecolor(markerfacecolor)
    421         self.set_markerfacecoloralt(markerfacecoloralt)
--> 422         self.set_markeredgecolor(markeredgecolor)
    423         self.set_markeredgewidth(markeredgewidth)
    424 

~/applications/anaconda3/lib/python3.5/site-packages/matplotlib/lines.py in set_markeredgecolor(self, ec)
   1180         if ec is None:
   1181             ec = 'auto'
-> 1182         if self._markeredgecolor != ec:
   1183             self.stale = True
   1184         self._markeredgecolor = ec

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

In [12]: mpl.__version__
Out[12]: '2.0.2'