title: creating a new dataframe based off if a particular value matches a value in a list
body: <p>What I have is data in a pandas dataframe.  There is one column that contains an customer_id.  These are not unique ids.  I have a list of selected customer ids (there are no repeating values in the list).  What I want to do is create a new dataframe based on the ids in the list.  I want all rows for each id in the list.  All the data has been read in as str.<br>
  Here is my code:</p>
  
  <pre><code>for i in range(len(df_ALL)):
  if df_ALL.loc[i,"Customer_ID"] in ID_list:
      df_Sub = df_Sub.append(df_ALL.iloc[i,:])
  </code></pre>
  
  <p>When I run this on simple small files it runs.  However when I run it on the real data it returns a "KeyError: 'the label [2666] is not in the [index]'"  I have only be using python/pandas for about 4-5 months, I tried to research a solution to this problem but I couldn't find something that I understood.  If there is a better method to accomplish my goal I am open to learning it.</p>
  
  <p>Thank you in advance.</p>