title: Python: Check if dataframe column contain string type
body: <p>I want check if columns in a dataframe consists of strings so I can label them with numbers for machine learning purposes. Some columns consists of numbers, I dont want to change them. Columns example can be seen below:</p>
  
  <pre><code>TRAIN FEATURES
    Age              Level  
    32.0              Silver      
    61.0              Silver  
    66.0              Silver      
    36.0              Gold      
    20.0              Silver     
    29.0              Silver     
    46.0              Silver  
    27.0              Silver      
  </code></pre>
  
  <p>Thank you=)</p>