title: change/writing single value to csv file python
body: <p>There is an error in my code :</p>
  
  <pre><code>_csv.Error: sequence expected
  </code></pre>
  
  <p>which i believe is because i am trying to write only one value not a list etc.</p>
  
  <pre><code> exRtFile = open ('exchangeRate.csv')
      exchReader = csv.reader(exRtFile)
      exchWriter = csv.writer(exRtFile)
      loop2=0
      while loop2==0:
          selected=int(input("Please select an option: "))
          if selected == 1:
              change = input("What rate would you like to change: ")
              changeRt = float(input("What would you like to change the rate to: "))
              for row in exchReader:
                  currency = row[0]
                  if currency == change:
                      crntRt = row[1]
                      crntRt = changeRt
                      exchWriter.writerow(crntRt)
                      exRtFile.close()
  </code></pre>
  
  <p>what would be the best way to fix this, or is there a better wayy to change a value in an CSV file?</p>
  
  <p>csv file:</p>
  
  <pre><code>Pound Sterling,1
  Euro,1.22
  US Dollar,1.67
  Japanese Yen,169.948
  </code></pre>