title: pandas: Convert int Series to new StringDtype
body: <p>I'm trying to convert an <code>UInt8</code> pandas series into the new <code>StringDtype</code>. </p>
  
  <p>I can do the following, covered in <a href="https://stackoverflow.com/questions/17950374/converting-a-column-within-pandas-dataframe-from-int-to-string">this question</a>, which predates the new <code>string</code> dtype:</p>
  
  <pre class="lang-py prettyprint-override"><code>import pandas as pd
  int_series = pd.Series(range(20), dtype="UInt8")
  obj_series = int_series.apply(str)
  </code></pre>
  
  <p>Which gives me a series of Object dtype containing strings. </p>
  
  <p>But if I try to convert the series to the new <code>string</code> dtype, I get an error:</p>
  
  <pre class="lang-py prettyprint-override"><code>&gt;&gt;&gt; string_series = int_series.astype("string")
  ...
  TypeError: data type not understood
  </code></pre>
  
  <p>Note that the first converting the series to <code>Object</code> and then to <code>string</code> dtype works:</p>
  
  <pre class="lang-py prettyprint-override"><code>int_series.apply(str).astype("string")
  </code></pre>
  
  <p>How can I convert the int series to string directly?</p>
  
  <p>I'm using pandas version 1.0.3 on Python 3.7.6</p>
  
  <hr>
  
  <p><strong>Update:</strong> I've found <a href="https://github.com/pandas-dev/pandas/issues/31204" rel="nofollow noreferrer">this open issue</a> in the pandas Github page that describes the exact same problem. </p>
  
  <p>A comment in the issue above points to <a href="https://github.com/pandas-dev/pandas/issues/22384" rel="nofollow noreferrer">another open issue</a> which covers the desired but currently not available functionality of converting between different ExtensionArray types. </p>
  
  <p>So the answer is that the direct conversion cannot be done now, but likely will be possible in the future. </p>