Day 2 – Lesson 8
Fruitful Functions
Python Mini-Course
University of Oklahoma
Department of Psychology
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Python Mini-Course: Day 2 - Lesson 8
05/02/09
Lesson objectives
1. Understand how to return values
from functions in Python
2. Create “fruitful” functions
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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
05/02/09
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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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
05/02/09
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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Python Mini-Course: Day 2 - Lesson 8
05/02/09
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
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Python Mini-Course: Day 2 - Lesson 8
05/02/09
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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Python Mini-Course: Day 2 - Lesson 8
05/02/09
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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Python Mini-Course: Day 2 - Lesson 8
05/02/09
Creating Boolean functions
 Functions that return a Boolean
value (True or False) can be
used in conditional statements
(i.e. if…else…)
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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
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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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Python Mini-Course: Day 2 - Lesson 8
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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
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Python Mini-Course: Day 2 - Lesson 8
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