Chapter 8: For & While Loops Revisited

• Recall that the forloop processes each item in a list

  • Each item in turn is (re-)assigned to the loop variable, and the body of the loop is executed

  for f in ["Joe", "Amy", "Brad", "Angelina", "Zuki", "Thandi", "Paris"]:
      print("Hi", f, "Please come to my party on Saturday")
  

• We have also seen iteration paired with the update idea to form the accumulator pattern

  • we could create a for loop using the rangeto produce the numbers 1 through n.
  • we can start with a running total variable initialized to 0 and on each iteration, add the current value of the loop variable.

  Example

  def sumTo(aBound):
      theSum = 0
      for aNumber in range(1, aBound + 1):
          theSum = theSum + aNumber
  
      return theSum
  
  print(sumTo(4))
  
  print(sumTo(1000))
  

  Zach’s Notes

  Very clever double loop

  • Run through two lists in one loop

  names = ["Aman", "Hritika", "Akanksha"]
  age = [22, 21, 24]
  index = 0
  for i in names:
      print("My Name is ", names[index], "I am ", age[index], "years old")
      index = index + 1
  
  '''Ouput
  My Name is  Aman I am  22 years old
  My Name is  Hritika I am  21 years old
  My Name is  Akanksha I am  24 years old
  '''
  

8.3 The while Statement

The example above but with a while loop (easier to understand imo)

def sumTo(aBound):
    """ Return the sum of 1+2+3 ... n """

    theSum  = 0
    aNumber = 1
    while aNumber <= aBound:
        theSum = theSum + aNumber
        aNumber = aNumber + 1
    return theSum

print(sumTo(4))

print(sumTo(1000))

More formally, here is the flow of execution for a while statement:

1. Evaluate the condition, yielding False or True.
2. If the condition is False, exit the while statement and continue execution at the next statement.
3. If the condition is True, execute each of the statements in the body and then go back to step 1.

Warning

• After the initial test, any following tests come only after the execution of the whole body, even if the condition becomes false in the middle of the loop body.
• The body of the loop should change the value of one or more variables so that eventually the condition becomes Falseand the loop terminates.