title: Pandas: Update values of a column
body: <p>I have a large dataframe with multiple columns (sample shown below). I want to update the values of one particular (population column) column by dividing the values of it by 1000.</p>
  
  <pre><code>City     Population
  Paris    23456
  Lisbon   123466
  Madrid   1254
  Pekin    86648
  </code></pre>
  
  <p>I have tried 
  <code>df['Population'].apply(lambda x: int(str(x))/1000)</code></p>
  
  <p>and </p>
  
  <pre><code>df['Population'].apply(lambda x: int(x)/1000)
  </code></pre>
  
  <p>Both give me the error</p>
  
  <blockquote>
    <p>ValueError: invalid literal for int() with base 10: '...'</p>
  </blockquote>