[prog] I don't understand this program (-- python) how does this work??

[Dan Richter]

Hi there.

It looks to me like your basic problem involves understanding lists and 
indexes.

Consider this program:
   my_list = ['foo', 'bar', 'baz']
   print my_list[0]     # Output is 'foo'.
   print my_list[1]     # Output is 'bar'.
   print my_list[2]     # Output is 'baz'.

In the last three lines, the number between the brackets is called an 
index. As Robert pointed out, in Python the first element of a list has 
index zero, the second index one, etc.

Now we're going to do the same thing using a variable instead of a constant 
index:
   my_list = ['foo', 'bar', 'baz']
   my_index = 0
   while my_index < len(my_list):
       print my_list[my_index]
       my_index = my_index + 1
This program outputs 'foo', then 'bar', the 'baz'.

Now consider a list of lists:
   list_of_lists = [ ['a','b','c'], ['d','e','f'] ]
   thing = list_of_lists[0]
   # In other words, thing = ['a','b','c']
   print thing[0]     # Output is 'a'.
   other_thing = list_of_lists[1]
   # In other words, other_thing = ['d','e','f']
   print other_thing[0]      # Output is 'd'.

I hope this helps.

========== Dan Richter ============== mailto:Dan at wimba.com ===========