title: Case insensitive pandas dataframe.merge
body: <p>I am struggling with the easiest way to do a case insensitive merge in pandas. Is there a way to do it right on the merge? Do I need to use (?i) or a regex with ignorecase? In my code snippet below I am joining some Countries where it may be "United States" in one file and "UNITED STATES" in another and I just want to take the case out of the equation. Thank you!</p>
  
  <pre><code>import pandas as pd
  import csv
  import sys
  
  env_path = sys.argv[1]
  map_path = sys.argv[2]
  
  
  df_address = pd.read_csv(env_path + "\\address.csv")
  df_CountryMapping = pd.read_csv(map_path + "\CountryMapping.csv")
  
  df_merged = df_address.merge(df_CountryMapping, left_on="Country", right_on="NAME", how="left")
  
  ....
  </code></pre>