title: Getting ggplot for Python to make a bar chart
body: <p>Following <a href="https://stackoverflow.com/questions/22599521/how-do-i-create-a-bar-chart-in-python-ggplot">this simple example</a>, I am trying to make a dirt simple bar chart using yhat's ggplot python module. Here is the <a href="https://stackoverflow.com/questions/22599521/how-do-i-create-a-bar-chart-in-python-ggplot">code suggested previously on StackOverflow</a>:</p>
  
  <pre><code>In [1]:
  from ggplot import *
  import pandas as pd
  df = pd.DataFrame({"x":[1,2,3,4], "y":[1,3,4,2]})
  ggplot(aes(x="x", weight="y"), df) + geom_bar()
  </code></pre>
  
  <p>But I get an error:</p>
  
  <pre><code>Out[1]:
  &lt;repr(&lt;ggplot.ggplot.ggplot at 0x104b18ad0&gt;) failed: UnboundLocalError: local variable 'ax' referenced before assignment&gt;
  </code></pre>