title: Why are my variables highlighted in blue?
body: <p>I have a dataframe called <code>propertydf</code>.</p>
  <p>When I run my code I get a very vague error:</p>
  <pre><code>propertydf = propertydf[propertydf['fixed_price'].notna()].copy()
               ^
  SyntaxError: invalid syntax
  </code></pre>
  <p>I checked the code and the dataframe variable has changed color to blue? But not all of them.</p>
  <p>I also noticed some other variables are suddenly blue, such as <code>year</code> and <code>date</code>.</p>
  <p>I think this is causing the error.  How can I fix it?</p>
  <p><a href="https://i.stack.imgur.com/J8Peo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/J8Peo.png" alt="enter image description here" /></a></p>