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

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

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

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

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

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

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

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

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

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

Lab 9 Questions?

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