Python Mini-Course

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Day 2 Lesson 8Fruitful Functions

• Python Mini-Course
• University of Oklahoma
• Department of Psychology

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Lesson objectives

1. Understand how to return values from functions in
   Python
2. Create fruitful functions

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The power function revisited

• def power(base, exponent)
• val base
• for x in range(1,exponent)
• val val base
• return val
• power(3,4)

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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

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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

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Exercise

• Create a function that computes the distance
  between any two points when given their
  coordinates (in 2-D space)

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Distance function

• def distance(x1, y1, x2, y2)
• """Return the distance between points
• (x1, y1) and (x2, y2) as a float"""
• return 0.0

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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

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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(dx2 dy2)
• return result

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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

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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)

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Creating Boolean functions

• Functions that return a Boolean value (True or
  False) can be used in conditional statements
  (i.e. ifelse)

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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)

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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

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Next session

• Iteration methods
• Recursion
• Loops and conditional execution
• The for loop
• The while loop
• Handling strings and text

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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