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functions_pt1.md

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Functions

  • What is a function? https://www.mathsisfun.com/sets/function.html
  • Functions are subprograms -- they are a sequence of of statements that have a name
  • Functions can be executed at any point by using their name
  • Functions remove duplicated code
  • Functions can call other functions
  • Functions can OPTIONALLY take parameters or inputs that they can use inside the function

Built-in functions

  • abs(-9) -- -9 is the input argument. Arguments appear between the parenthesis after the function name
day_temperature = 3
night_temprature = 10
abs(day_temperature - night_temprature)

Because function calls produce values, they can be used in expressions:

abs(-7) + abs(3.3)

Functions to convert one type of variable to another

int(34.6)
int(-4.3)
float(21)
str(21)

The Round function can round floats

round(3.8)
round(3.3)
round(3.5)
round(-3.3)
round(-3.5)

The round function can take an OPTIONAL second argument

round(3.141592653,2)

The help(fxn) function gives information about a function

help(round)
help(pow)

Using the pow function

pow(2, 4)
pow(2, 4, 3)

We can also use function calls as arguments to other functions:

pow(abs(-2), round(4.3))

You can use the id() function to find the memory address of objects.

id(-9)
id(23.1)
shoe_size = 8.5
id(show_size)

Some other useful functions

min(2, 3, 4)
max(2, -3, 4, 7, -5)
max(2, -3, min(4, 7), -5)

Defining your own functions

  • The built-in functions (e.g, type, print, input) that Python provides do basic tasks. We can write our own functions that can execute complicated sequence of instructions. Your functions will be made up of Python operators and built-in Python functions.

Designing New Functions: A Recipe

  • What do you name the function?
  • What are the parameters, and what types of information do they refer to?
  • What calculations are you doing with that information?
  • What information does the function return?
  • Does it work like you expect it to? -- We will not cover in this class.
def f(x):
    squared_x  = x * x
    return squared_x
def f(x):
    squared_x = x ** 2
    return squared_x
def f(x):
    squared_x = pow(x, 2)
    return squared_x
def f(x):
    return x**2
def f(x):
    return pow(x, 2)

Variations in functions

  • No input; no output; example -- print something
  • One or more input; no output; example -- print the input
  • One or more input: one or more output; example -- take two numbers and return their sum
  • No input; one or more output; example -- a random number

Function Exercises

  • Function Exercises 1-12