PYTHONFUNCTIONS : CHAPTER 3

FROM

THINK PYTHON

HOW TO THINK LIKE A COMPUTER SCIENTIST

TYPE CONVERSION FUNCTIONS

A function in Python is a named sequence of instructions that perform a computation. When a function is called it returns the result of this computation.

>>> type ( 23.4)

<class ‘float’)> returned value

>>> int(23.4)

23 returned value is now an integer

>>>float(45)

45.0 returns a float

>>>str(456)

‘456’

MATHEMATICAL FUNCTIONS>>> import math

>>> math.sqrt(45)

6.708203932499369

>>> r=5

>>>3/4.0*math.pi*r**3

294.5243112740431

>>> math.log(100,2) log of 100 base 2

6.643856189774725

>>> math.sin(math.pi)

1.2246467991473532e-16 what in the world is this?

Study the trig example in exercise 3

NEW FUNCTIONS YOU WRITE

Type in the following script within the editor and run it

import math

def vol_of_sphere(radius): : is REQUIRED

vol = 4/3.0*math.pi*radius**3 indention is required

return vol

print vol_of_sphere(5)

>>>

523.598775598 output that you’ve seen before

>>>

FUNCTION PARTS

def vol_of_sphere(radius): header

vol = 4/3.0*math.pi*radius**3

return vol

Argument(sent in)radius is called a parameter.

Function definition

Value to return

body

Use four spaces for the indention

FUNCTION TO FIND THE AREA OF A TRIANGLESee Herons formula (http://mathworld.wolfram.com/HeronsFormula.html)

# Herons formula as a script

import math

def area(a, b, c):

“”” a, b and c are the sides of a triangle “”” function info

s = 1/2.0*(a+b+c)

a = math.sqrt(s*(s-a)*(s-b)*(s-c))

return a

print area(1,1,1)

>>>

0.433012701892

>>>

FUNCTION FLOW OF EXECUTION

Inst

Inst

Inst

Inst

print area(5,5,6)

Inst

Inst

Inst

def area(a, b, c): s = 1/2.0*(a+b+c) a = math.sqrt(s*(s-a)*(s-b)*(s-c)) return a

Be sure and define your functions before you use them!

FUNCTION VARIABLES AND PARAMETERS ARE LOCALimport math

#Define the function here

def area(a, b, c):

""" a, b and c are the sides of a triangle """

s = 1/2.0*(a+b+c)

area = math.sqrt(s*(s-a)*(s-b)*(s-c))

return area

#The linear part of this program starts here

s = 25

a=2

print area(1,1,1)

print s,a

#here is the output>>> 0.43301270189225 2>>>

IN CLASS PROBLEM

1. Write a function called FtoC that will convert Fahrenheit to Celsius. You will need a single parameter. Run the program to test it with some know values.

C = 5/9(F -32) F=9/5C + 32

2. Write a function to return the volume of a sphere of radius r

WHY FUNCTIONS?• Lets you name a group of statements, which makes your

program easier to read.

• Functions make programs smaller by being able to reuse the same code.

• Dividing programs into functions allow you to debug sections at a time.

• Well defined functions can be used in other programs that you write.

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Note: if you do this from math import * instead of import math you will not need to include the math. prefix