CS 111 f21 — Functions and Conditionals part 2

Table of Contents

1 Lab 1 questions

  • You will be adding functions (strategies) to prisoner2.py and prisoner3.py where it says 

    # DEFINE STRATEGIES HERE
  • All of these functions have as parameters the history of the current player (my_history) and the opponent (other_history).
  • These history objects have functions associated with them (listed in the History documentation)
    • Functions associated with particular objects are called methods
    • We can use these functions to ask a particular history for information

    • For example, 

      my_history.get_length()

      returns the number of actions in my_history. How could we use that in an if statement to check if it is the first round of the game?1

    • As the lab writeup says, Python automatically fills in the self parameters for us. We will learn more about self later, but for now we can just ignore it.
  • How would we find out the number of times our opponent has cooperated?2

2 Review

  • In what order will these lines be executed3 

    1: cur_temp = 28
2: def C_to_F(temp_C):
3:     temp_F = temp_C * 9 / 5 + 32
4:     return temp_F
5: cur_temp_F = C_to_F(cur_temp)
6: print(cur_temp_F)

3 Functions

  • Why might we want to use functions?
  • Possible errors
    • Wrong number of inputs
    • Unindenting something that should be part of the function

4 Practice

  • Write an average_grade function that takes three numeric grades as parameters and returns their average4
  • Function mysteries

    • What will be printed?5 

      def     f(x):
    return x + 2
def     g(y):
    return y * 3
a = 2
print(f(g(a)), g(f(a)))

    • What will be printed?6 

      def     f(x):
    return x + 2
def     g(y):
    return f(y) * f(y + 1)
a = 2
print(g(a))

5 Conditionals

  • Since the start of the term we've been talking about having a computer make a decision based on some condition (e.g., decide what weather icon to display)

  • We can do this with Python's if 

    if CONDITION:
    print("this is only printed when CONDITION is True")
print("this is always printed")

  • We can use if-else to cause the computer to take one of two different paths 

    if CONDITION:
    print("this is only printed when CONDITION is True")
else:
    print("this is only printed when CONDITION is False")
print("this is always printed")
  • What if we want the text to have more than settings (normal, yellow, red)?

    • Could do something like 

      if cur_temp > hot_temp_C:
    # print in red
else:
    if cur_temp > hot_temp_C - 5:
       # print in yellow
    else:
       # print normally

      but this would quickly get cumbersome with tons of indenting as the number of different outcomes grew

  • Instead, we can use if-elif-else 

    if cur_temp > hot_temp_C:
    # print in red
elif cur_temp > hot_temp_C - 5:
    # print in yellow
else:
    # print normally

  • What if we had multiple conditions? 

    if cur_temp > hot_temp_C:
    if chance_of_rain > 0.4:
        # display text in red with cloudy icon
    elif chance_of_clouds > 0.5:
        # display text in red with cloudy icon
else:
   # ...

    • We can use and and or to combine several Boolean expressions into a single condition 

      if cur_temp > hot_temp_C and (chance_of_rain > 0.4 or chance_of_clouds > 0.5):
    # display text in red with cloudy icon
else:
    # ...
      • A and B will be True when both A and B are True
      • A or B will be True when either A or B is True
        • Also when both A and B are True

6 Practice

  • Write an absolute value function: takes one number as a parameter, returns the positive version of that number (hint: if x is negative, -x is the positive version).7
  • Mystery

    • What will be printed?8 

      def     is_even(x):
    return x % 2 == 0
turns = 7
if turns == 0:
    print("WELCOME")
elif is_even(turns):
    print("FOR FUN")
else:
    print("IT'S TIME")
  • Given a player's guess and a secret number, print "cold" "warm" or "lava" (or "WINNER" if the guess is correct)9
    • Assume you have a variable guess with the player's guess and a variable secret with the secret number
    • Up to you to choose how close "lava" is, etc.
    • Make sure to only print one hint

Footnotes:

1 
if my_history.get_lenth() == 0:
2

Ask other_history! 

opponent_cooperations = other_history.get_num_coops()
3

1,2,5,3,4,6

4 
def average_grade(grade1, grade2, grade3):
    return (grade1 + grade2 + grade3) / 3
5

8 12

6

20

7 
def abs(x):
    if x < 0:
        return -x
    else:
        return x
8

"IT'S TIME"

9 
difference = abs(secret - guess)
if difference == 0:
    print("WINNER")
elif difference < 5:
    print("lava")
elif difference < 10:
    print("warm")
else:
    print("cold")