def show_rgb_hist(image):
    colours = ('r','g','b')
    for i, c in enumerate(colours):
        plt.figure(figsize=(20, 4))
        histr = cv2.calcHist([image], [i], None, [256], [0, 256])
#         plt.plot(histr, color=c, lw=2)
#         print(histr.ravel())
        
        if c == 'r': 
            colours = [((i/256, 0, 0)) for i in range(0, 256)]

        if c == 'g': 
            colours = [((0, i/256, 0)) for i in range(0, 256)]

        if c == 'b': 
            colours = [((0, 0, i/256)) for i in range(0, 256)]

        
        plt.bar(range(0, 256), histr, color=colours, edgecolor=colours, width=1)
#         plt.xlim([0, 256])

        plt.show()
    
show_rgb_hist(image)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-47-eb26539e3a3c> in <module>()
     22         plt.show()
     23 
---> 24 show_rgb_hist(image)

<ipython-input-47-eb26539e3a3c> in show_rgb_hist(image)
     17 
     18 
---> 19         plt.bar(range(0, 256), histr, color=colours, edgecolor=colours, width=1)
     20 #         plt.xlim([0, 256])
     21 

~/anaconda3/lib/python3.6/site-packages/matplotlib/pyplot.py in bar(*args, **kwargs)
   2646                       mplDeprecation)
   2647     try:
-> 2648         ret = ax.bar(*args, **kwargs)
   2649     finally:
   2650         ax._hold = washold

~/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py in inner(ax, *args, **kwargs)
   1715                     warnings.warn(msg % (label_namer, func.__name__),
   1716                                   RuntimeWarning, stacklevel=2)
-> 1717             return func(ax, *args, **kwargs)
   1718         pre_doc = inner.__doc__
   1719         if pre_doc is None:

~/anaconda3/lib/python3.6/site-packages/matplotlib/axes/_axes.py in bar(self, *args, **kwargs)
   2083                 edgecolor=e,
   2084                 linewidth=lw,
-> 2085                 label='_nolegend_',
   2086                 )
   2087             r.update(kwargs)

~/anaconda3/lib/python3.6/site-packages/matplotlib/patches.py in __init__(self, xy, width, height, angle, **kwargs)
    657         """
    658 
--> 659         Patch.__init__(self, **kwargs)
    660 
    661         self._x = xy[0]

~/anaconda3/lib/python3.6/site-packages/matplotlib/patches.py in __init__(self, edgecolor, facecolor, color, linewidth, linestyle, antialiased, hatch, fill, capstyle, joinstyle, **kwargs)
    101         self.set_fill(fill)
    102         self.set_linestyle(linestyle)
--> 103         self.set_linewidth(linewidth)
    104         self.set_antialiased(antialiased)
    105         self.set_hatch(hatch)

~/anaconda3/lib/python3.6/site-packages/matplotlib/patches.py in set_linewidth(self, w)
    349                 w = mpl.rcParams['axes.linewidth']
    350 
--> 351         self._linewidth = float(w)
    352         # scale the dash pattern by the linewidth
    353         offset, ls = self._us_dashes

TypeError: only size-1 arrays can be converted to Python scalars

cv2.__version__
'3.4.1'