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Python Functions : chapter 3

Python Functions : 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)

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Python Functions : chapter 3

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  1. PythonFunctions : chapter 3 From Think Python How to Think Like a Computer Scientist

  2. 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) • returned value is now an integer • >>>float(45) • 45.0 returns a float • >>>str(456) • ‘456’

  3. 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

  4. New Functions you write • Type in the following script within the editor and run it • import math • defvol_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 • >>>

  5. Function parts Argument(sent in) radius is called a parameter. • defvol_of_sphere(radius): header • vol= 4/3.0*math.pi*radius**3 • return vol body Function definition Value to return Use four spaces for the indention

  6. Function to find the area of a triangle • See 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 • >>>

  7. 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!

  8. Function Variables and Parameters are Local • import 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 >>> 0.433012701892 25 2 >>>

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

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

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