1. Python Mini-Course University of Oklahoma Department of Psychology Day 2 – Lesson 8 Fruitful Functions 05/02/09 Python Mini-Course: Day 2 - Lesson 8 1

2. Lesson objectives 1. Understand how to return values from functions in Python 2. Create “fruitful” functions 05/02/09 Python Mini-Course: Day 2 - Lesson 8 2

3. The power function revisited def power(base, exponent): val = base for x in range(1,exponent): val = val * base return val power(3,4) 05/02/09 Python Mini-Course: Day 2 - Lesson 8 3

4. The return statement Syntax return [expression] Exists the enclosing function and returns the value of expression as a result of the call to the function If expression is omitted, returns None 05/02/09 Python Mini-Course: Day 2 - Lesson 8 4

5. The return statement You can only return one value That value can be any Python data type (including both built-in and custom data structures) You can also use the return statement to exit a function early 05/02/09 Python Mini-Course: Day 2 - Lesson 8 5

6. Exercise Create a function that computes the distance between any two points when given their coordinates (in 2-D space) 05/02/09 Python Mini-Course: Day 2 - Lesson 8 6

7. Distance function def distance(x1, y1, x2, y2): """Return the distance between points (x1, y1) and (x2, y2) as a float""" return 0.0 05/02/09 Python Mini-Course: Day 2 - Lesson 8 7

8. Distance function def distance(x1, y1, x2, y2): """Return the distance between points (x1, y1) and (x2, y2) as a float""" dx = x2 - x1 dy = y2 - y1 print 'dx is ', dx print 'dy is ', dy return 0.0 05/02/09 Python Mini-Course: Day 2 - Lesson 8 8

9. Distance function def distance(x1, y1, x2, y2): """Return the distance between points (x1, y1) and (x2, y2) as a float""" dx, dy = x2 - x1, y2 - y1 result = math.sqrt(dx**2 + dy**2) return result 05/02/09 Python Mini-Course: Day 2 - Lesson 8 9

10. Distance function def distance(x1, y1, x2, y2): """Return the distance between points (x1, y1) and (x2, y2) as a float""" result = \ math.sqrt((x2-x1)**2 + (y2-y1)**2) return result 05/02/09 Python Mini-Course: Day 2 - Lesson 8 10

11. Distance function def distance(x1, y1, x2, y2): """Return the distance between points (x1, y1) and (x2, y2) as a float""" return math.sqrt((x2-x1)**2 + (y2-y1)**2) 05/02/09 Python Mini-Course: Day 2 - Lesson 8 11

12. Creating Boolean functions Functions that return a Boolean value ( True or False ) can be used in conditional statements (i.e. if…else… ) 05/02/09 Python Mini-Course: Day 2 - Lesson 8 12

13. is_divisible function def is_divisible(x, y): if x % y == 0: return True else: return False is_divisible(16,4) is_divisible(16,3) 05/02/09 Python Mini-Course: Day 2 - Lesson 8 13

14. is_divisible function def is_divisible(x, y): return x % y == 0 is_divisible(16,4) is_divisible(16,3) x, y = 16, 5 if is_divisible(x, y): print x,'is divisible by',y 05/02/09 Python Mini-Course: Day 2 - Lesson 8 14

15. Next session Iteration methods: Recursion Loops and conditional execution The for loop The while loop Handling strings and text 05/02/09 Python Mini-Course: Day 2 - Lesson 8 15

16. Suggested exercises Exercise 5.1 – Fermat's Last Theorem Exercise 6.6 – Palindromes Exercise 6.7 – is_power function Turtle exercises from Chaps 4 & 5 05/02/09 Python Mini-Course: Day 2 - Lesson 8 16