python05():
  Exercises for loops.

  Evaluate triangular numbers for 0 <= n < 11.

  t( 0 ) =  0.0
  t( 1 ) =  1.0
  t( 2 ) =  3.0
  t( 3 ) =  6.0
  t( 4 ) =  10.0
  t( 5 ) =  15.0
  t( 6 ) =  21.0
  t( 7 ) =  28.0
  t( 8 ) =  36.0
  t( 9 ) =  45.0
  t( 10 ) =  55.0

  Repeat calculation, using // for integer division.

  t( 0 ) =  0
  t( 1 ) =  1
  t( 2 ) =  3
  t( 3 ) =  6
  t( 4 ) =  10
  t( 5 ) =  15
  t( 6 ) =  21
  t( 7 ) =  28
  t( 8 ) =  36
  t( 9 ) =  45
  t( 10 ) =  55

  Non-indented statements before and after loop.

  S starts out at  0
  t( 1 ) =  1
  t( 2 ) =  3
  t( 3 ) =  6
  t( 4 ) =  10
  t( 5 ) =  15
  t( 6 ) =  21
  t( 7 ) =  28
  t( 8 ) =  36
  t( 9 ) =  45
  t( 10 ) =  55
  Sum of triangular numbers is  220

  The range statement returns a list of loop indices.

  range ( 10 ) =  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  range ( 0, 10 ) =  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  range ( 10, 10 ) =  []
  range ( 10, 0 ) =  []
  range ( 10, 0, -1 ) =  [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
  range ( 0, 10, 2 ) =  [0, 2, 4, 6, 8]

  We can use a list instead of range().

  UScoins =  [1, 5, 10, 25, 50, 100]
  The sum of a collection of US coins is  191

  friends =  ['Alice', 'Bob', 'Carol', 'David']
  My friend Alice has a name of length  5
  My friend Bob has a name of length  3
  My friend Carol has a name of length  5
  My friend David has a name of length  5

  patient0 =  ['Robert Baratheon', 235.4, 73, False]
  patient1 =  ['Arya Stark', 134.7, 68, True]
  patients =  [['Robert Baratheon', 235.4, 73, False], ['Arya Stark', 134.7, 68, True]]
Robert Baratheon  weighs  235.4 lbs and is  73 inches tall.
Arya Stark  weighs  134.7 lbs and is  68 inches tall.

  A nested loop allows us to process matrix entries.

  A =  [[0.03757387 0.34131639 0.99354428]
 [0.3520471  0.94363297 0.15407962]
 [0.48228158 0.55489399 0.18388203]
 [0.92389241 0.37971198 0.11977826]]

  average matrix entry is  0.4555528734472701

  While loop for triangular numbers.

 1000 <= t( 45 ) =  1035