Concepts

• None
  • is an object
  • function: return None or return or no return
  • can be used to set a variable
    • is not the same as zero or blank
  • can be as default for function argument
    • this is beyond what we have covered in class.
      • if parameter is mutable, does not retain the paramter value
• homeworks with docstrings

While Loops

• loop body
• expression
  • evaluated before entering the loop body
• iteration
• loop should terminate eventually
  • boolean expression evaluates to false
  • sentinel value

count = int(input("enter an integer number: "))
while count < 10 and count % 7 != 0:
    print(count)
    count += 1

• compare to

count = int(input("enter an integer number: "))
while count < 10 and count % 7 != 0:
    print(count)
count += 1

While loop and validating user input

amount = float(input("Enter Withdrawal Amount: "))

while (amount < 1.0 or amount > 300.0):
   print("Amount must be $1.00 - $300.00.")
   amount = float(input("Enter Withdrawal Amount: "))


print(f"Here is what you entered {amount:.2f}")

How many times is the loop body executed?

How many times is the boolean expression executed?

What is the output?

grades = [93, 82, 67, 99]
while len(grades) > 1:
    min_grade = min(grades)
    print(min_grade)
    grades.remove(min_grade)
print(grades[0])

Tracing output: predict results on paper

# Problem 1
count = 1
while count <= 3:
    count += 1
    print(count)

# Problem 2
count = 7
while count > 3:
    print(count)
    count -= 2

# Problem 3
count = 10
while count > 0:
    count += 1
    print(count)

Random numbers

• want to generate pseudo random numbers
  • seed based on current time
• random module
• random.random(): returns a float from 0.0(inclusive) to 1.0 (exclusive)
• random.randrange(x): returns an integers from 0 to x-1
• random.randrange(min, max): returns an integer from min to max-1
• random.randint(min, max): returns an integer from min to max
• random.seed(number): can reproduce the series of random numbers