Wednesday 9/27

Introduction to for Loops

Basics

For loops perform the same operation for each element in a collection:

colors = ["red", "blue", "green"]
for c in colors:
    print("Color is: ", c)

This will print:

Color is:  red
Color is:  blue
Color is:  green

Finding the Maximum Item

One common task is looping through a list to find the maximum item (or the minimimum). This is one way to do it:

def get_max(numbers):
    biggest = -float('inf')  # Top of the hill
    for num in numbers:
        if num > biggest:
            biggest = num    # New king of the hill!
    return biggest

Looping by Index

Usually our for loops just need to process each element in a list, we don't care about the index of the elements.

Sometimes, we do need to know the index. For example, we might want a function that returns the position of the maximum element in a list. In this cases we can use the range function to generate all of the necessary index values.

def get_max_index(numbers):
    biggest = -float('inf')  # Top of the hill
    biggest_index = -1       # Invalid placeholder
    for i in range(len(numbers)):
        if numbers[i] > biggest:
            biggest = numbers[i]  # New king of the hill!
            biggest_index = i
    return biggest_index

Quiz Instructions

• Log into the desktop as student with no password.
• Log into Canvas.
• Wait until the instuctor says to start before accessing Part 1.
• The quiz can be found in the "Modules" section of Canvas.
• The entire quiz has a 25 minute time limit.
• Part 1 (Conceptual):
  • You may not use Thonny (or any other resources) for Part 1.
  • There is a 15 minute time limit for Part 1 (I suggest you don't use that much time!)
  • Raise your hand when you complete Part 1, and we will provide the Part 2 instructions.
• Part 2 (Coding):
  • You have unlimited submissions.
  • You do NOT need to provide docstrings.
  • The autograder will NOT check for PEP8 violations (though you should still use good style.)
  • You must use Thonny as your editor.
  • You may not access any external web pages or other resources.