title: Processing multiple files in Python, and matching on fields
body: <p>I have a number of CSV files which I need to compare to one 'Master List', and determine, based on a unique ID, if these other files contain entries for that key.</p>
  
  <p>What would the easiest way to do this in Python be? I.e what kind of structures would you suggest I read the data into, and how would you suggest I iterate through it?</p>
  
  <p>Here is an example of the data and output I am looking for.</p>
  
  <pre><code>**Master List**
  
  Unique ID : File Name : File Version : Responsible Party
  
  J578221 : Expander : 1.23 : Joe Bloggs
  
  KK89821 : Top : 0.9 : Mike Smith
  
  
  **Location X**
  
  Region : File Name : Unique ID
  
  USA : Acme Expander : J578221
  
  USA : Acme Tail : MK33431
  
  **Location Z**
  
  Reqion : File Name : Unique ID : Date Added
  
  China : Expander : J578221 : 03-04-2012
  
  HK : Acme Top : KK89821 : 06-07-2012
  
  **Output:**
  
  Unique ID : File Name : File Version : Responsible Party : In Location X : In Location Z
  
  J578221 : Expander : 1.23 : Joe Bloggs : YES : YES
  
  KK89821 : Top : 0.9 : Mike Smith : NO : YES
  </code></pre>