title: How to replace question mark in value of a panda frame as missing value?
body: <p>This is the code I have used:</p>
  
  <pre><code>diabetic_df.replace({'weight': {'?': ""}}, regex=False)
  </code></pre>
  
  <p>However it does not show up as missing value when I run the code below"</p>
  
  <pre><code>diabetic_df.isnull().sum()
  </code></pre>
  
  <p>Would you be able to advise what I have done wrong?</p>