title: Drop rows that do not contain a string within a value using pandas
body: <p>I want to use python pandas to drop rows in a spreadsheet that do not contain "CAT" within the "Equipment" column.
  Here is what I have so far:</p>
  
  <pre><code>import pandas as pd
  import openpyxl
  import warnings
  import xlrd
  
  warnings.filterwarnings("ignore")
  
  file_name = input("Enter File Name: ")
  df = pd.read_csv(file_name)
  
  
  for i in range(len(df["Equipment"])):
      if "CAT" in df["Equipment"][i]:
          print (df["Equipment"][i])
      else:
          df.drop([i])
  
  df.to_excel("new_mp.xlsx")
  </code></pre>
  
  <p>The script prints out the correct values in the terminal but does not drop the rows in the new spreadsheet "new_mp.xlsx". Can someone point me in the right direction?</p>
  
  <p>Example Data:</p>
  
  <pre><code>Equipment
  CAT 259B3 1818 OE Skid Steer 2011 CAT
  T-14 Towmaster Trailer 3124 OE Trailer 2008
  CAT 938M Loader RPO RENTAL 2017 CAT 938M
  Rental Water Truck 55571 Rental Water Truck international water truck
  </code></pre>