1. More on Functions (Part 2)
Intro to Computer Science
CS1510, Section 2
Dr. Sarah Diesburg

2. What are functions?
Little pieces of code that we can write and invoke by name
Reusable
General

3. Functions Take in any number of parameters Possibly compute something
Including no parameters!
Possibly compute something
Return a value
Can be None
If no return is specified, returns None

4. Function that takes in no parameters
def answerToEverything():
return 42
This function takes in no parameters
It does no computation
Just returns a number

5. Function that returns nothing
Let’s take a look at print()
>>> result = print(“hi”)
>>> print(result)
None
>>>

6. None None is a special value in Python that represents nothing
The first letter of None must be capitalized – it will turn orange
Use it when you have nothing to return
Like if one of the parameters was invalid

7. Functions
Remember, a function stops running when it hits a return statement
Often times it is easier to write something as a function than as a script by itself
Let’s look at our old script to find a prime number

8. prime.py
number = int(input("Please enter a number greater than 2. ")) isPrime = True #break out condition divisor = 2 while divisor<number and isPrime: if number%divisor==0: print("The number",number,"is divisible by",\ divisor) isPrime=False # Going to break out divisor=divisor+1

9. prime.py (continued)
if isPrime: print("That number is prime") else: print("That number is NOT prime")

10. primeAsFunction.py def isPrime(number):
for divisor in range(2,number):
if number%divisor==0:
return False
return True
Much smaller!

11. Lab 9
Questions?

12. Exam #2 Same format as Exam #1 Over Chapters 3-5
Does not include functions
Study guide now available