title: Pandas - Behaviour/Issue of reindex vs loc for setting values
body: <p>I've been trying to use <code>reindex</code> instead of <code>loc</code> in pandas as from 0.24 there is a warning about reindexing with lists.</p>
  
  <p>The issue I have is that I use <code>loc</code> to change the values of my dataframes.<br>
  Now if use reindex i lose this and if I try to be smart I even get a bug.</p>
  
  <p>Contemplate the following case:</p>
  
  <pre><code>df = pd.DataFrame(data=pd.np.zeros(4, 2), columns=['a', 'b'])
  ds = pd.Series(data=[1]*3)
  </code></pre>
  
  <p>I want to change a subset of values (while retaining the others), so <code>df</code> keeps the same shape.</p>
  
  <p>So this is the original behaviour which works (and changes the values in a subset of df['a'] to 1)</p>
  
  <pre><code>df.loc[range(3), 'a'] = ds
  </code></pre>
  
  <p>But when I'm using the reindex I fail to change anything:</p>
  
  <pre><code>df.reindex(range(3)).loc['a'] = ds
  </code></pre>
  
  <p>Now when I try something like this:</p>
  
  <pre><code>df.loc[:, 'a'].reindex(range(3)) = ds
  </code></pre>
  
  <p>I get a <code>SyntaxError: can't assign to function call</code> error message.</p>
  
  <p>For reference I am using pandas 0.24 and python 3.6.8</p>