CPSC120B
Fundamentals of Computer Science

Machine Learning

• A Neural Network Playground

Reading Questions

Quiz

For Loops

• For loops allow you to do something repeatedly
• If you ever find yourself copying and pasting code it might be an indication that a for loop is appropriate.

• For example the star program from the first lab

  import turtle
  length = 100
  angle = 144
  turtle.forward(length)
  turtle.left(angle)
  turtle.forward(length)
  turtle.left(angle)
  turtle.forward(length)
  turtle.left(angle)
  turtle.forward(length)
  turtle.left(angle)
  turtle.forward(length)
  turtle.left(angle)

• Has two lines that are duplicated 5 times

• This can be rewritten using a loop

  import turtle
  length = 100
  angle = 144
  for i in [1, 2, 3, 4, 5]:
      turtle.forward(length)
      turtle.left(angle)

• Note, the code that is repeated is indented

• Don’t forget the colon at the end of the for line

Range

• Writing in 1, 2, 3, 4, 5, gets annoying if you want a loop to run a lot of times
• Furthermore, if you want a loop to run some number of times based on user input, you don’t know how many numbers to put in the brackets
• The range function makes this possible

• The looping star program

  import turtle
  length = 100
  angle = 144
  for i in [1, 2, 3, 4, 5]:
      turtle.forward(length)
      turtle.left(angle)

• Becomes

  import turtle
  length = 100
  angle = 144
  for i in range(5):
      turtle.forward(length)
      turtle.left(angle)

• The number in the parentheses is the number of times the loop will run

Activity