title: Saving DataFrame to csv but output cells type becomes number instead of text
body: <pre><code>import pandas as pd
  check = pd.read_csv('1.csv')
  nocheck = check['CUSIP'].str[:-1]
  nocheck = nocheck.to_frame()
  nocheck['CUSIP'] = nocheck['CUSIP'].astype(str)
  nocheck.to_csv('NoCheck.csv')
  </code></pre>
  
  <p>This works but while writing the csv, a value for an identifier like 0003418 (type = str) converts to 3418 (type = general) when the csv file is opened in Excel. How do I avoid this?</p>