Editing DS4UX (Spring 2016)/Day 3 follow up (section)

=== Iterating an indeterminate number of times with <code>while</code> loops ===
Use <code>while</code> loops when you don't know how many times you want to repeat ("iterate") an operation. 

 grocery_list = []
 testAnswer = input('Press y if you want to enter more groceries: ')
 while testAnswer == 'y':
     food = input('Next item:')
     grocery_list.append(food)
     testAnswer = input('Press y if you want to enter more groceries: ')

 print('Your grocery list:')
 for food in grocery_list:
     print(food)

Most of the time, you will find that <code>for</code> loops are more common for the kind of coding that you will be doing. For example, if you are reading through a CSV file, a <code>for</code> loop makes perfect sense: there are a set number of lines in the file, and you want to loop through the file line by line until you reach the end of the file. However, whenever your code is accepting input from a person or an API, you may find that you don't ''know'' ahead of time how many times you will need to perform an operation before stopping. In these cases, it's useful to know how to keep looping until a particular condition is met, and then stop.