title: ValueError: Unrecognized character a in format string
body: <p>I have this data set that outputs strange error when I try to call its values. Unsure about where I am going wrong.
  where data1 is the dictionary, it outputs the following error:</p>
  <pre><code>~\anaconda3\lib\site-packages\matplotlib\axes\_base.py in _plot_args(self, tup, kwargs)
      310     def _plot_args(self, tup, kwargs):
      311         if len(tup) &gt; 1 and isinstance(tup[-1], str):
  --&gt; 312             linestyle, marker, color = _process_plot_format(tup[-1])
      313             tup = tup[:-1]
      314         elif len(tup) == 3:
  
  ~\anaconda3\lib\site-packages\matplotlib\axes\_base.py in _process_plot_format(fmt)
      102             i += 2
      103         else:
  --&gt; 104             raise ValueError(
      105                 'Unrecognized character %c in format string' % c)
      106 
  
  ValueError: Unrecognized character a in format string
  
  
  </code></pre>
  <p>I have extracted the type of both the dictionary and both value sets. The dictionary is a dict and the value sets for both are lists.</p>
  <p>However, when I plot it the following way, it works:</p>
  <pre><code>plt.figure()
  x= data1['date']
  y = data1['value']
  plt.plot(x,y)
  </code></pre>
  <p>What could be going wrong?</p>