Lecture 15 --- For Loops
================================

Basics
-------------------------

-  ``for`` loops tend to have a fixed number of iterations computed at
   the start of the loop.

-  ``while`` loops tend to have an indefinite termination, determined by
   the conditions of the data.

-  Most Python ``for`` loops are easily rewritten as ``while`` loops,
   but not vice-versa.


Overview of Today
-----------------

-  Ranges and control of for loop iterations

-  Nested loops

-  Lists of lists



Part 1: Range in For Loops
----------------------------

-  :func:`range` is a function to generate a sequence of integers:

   ::

       for i in range(10):
           print(i)

   outputs digits 0 through 9 in succession, one per line.

   -  Remember that this is up to and **not including** the end
      value specified! 

-  A range is not quite a list --- instead it generates values for each
   successive iteration of a ``for`` loop.

-  If we want to start with something other than 0, we provide two
   integer values:

   ::

       >>> list(range(3, 8))
       [3, 4, 5, 6, 7]

-  With a third integer values we can create increments. For example:

   ::

       >>> list(range(4, 20, 3))
       [4, 7, 10, 13, 16, 19]

   starts at 4, increments by 3, stops when 20 is reached or surpassed.

-  We can create backwards increments:

   ::

       >>> list(range(-1, -10, -1))
       [-1, -2, -3, -4, -5, -6, -7, -8, -9]  


Lecture Slides
---------------

https://drive.google.com/file/d/1opljzyih3jpsOxZXSMQzmxHGlIAhWHc8/view?usp=sharing

Lecture Video
---------------

https://www.youtube.com/watch?v=xo65l_YbMZA