ACM init()Day 4: May 12, 2015

From last time• Loops!

• While loop- don't make them infinite!

• While-else

• For loops

• For-else loops exist as well

Functions• A function is a reusable section of code written to

perform a specific task in a program.

• Why use functions?

• If there is a mistake in your program it is much easier to debug if everything is separated out

• If you need to do the same thing over and over again a function can reduce repetition

Example

First challengeModify the function to find the factorial of any number the user

inputs.

Answer

This is review.

How do we write a function?A function has two parts: a name and a body.

def function_name(optional args): code you want to run

Don't forget the ':'!

Function examples

How do we use a function?Calling a function is easy! All you have to do is type the

function's name. For example, if we wanted a function that tells us "Hi," we would do this:

The () are where you can put optional arguments.

Function with arguments

This function computes the area of a rectangle. It takes two arguments: the lengths of the sides.

Challenge

Write a function that multiplies any two numbers the user types in. Print out the result.

Answer

New challenge

Using the same multiply function, modify the program so it also squares the product of the two numbers.

!For example, if the input is (2,3) the result should be 36.

!You cannot modify the multiply function!

Answer

We can call a function from another function!

Try this!

Write a by_three function that takes a single integer parameter, num, and returns True if that number is evenly divisible by

three and False if not. Print out a statement with your results.

Answer

Importing

I'm lazy. I don't like constantly writing my own functions. Python has some built in for us! We have to import them though.

Try this!What if we want to take the square root of a number.

Fix it by importing a math library

First tell Python we want to use the math library. Then whenever you use a function from that library put 'math' in front

of it to access it!This works.

The math librarymath has a lot of functions you can use. For example:

exponent log sin pi

factorial ...

https://docs.python.org/2/library/math.html

Let's be even lazier!

Typing math.function() constantly is annoying. If we only want to use one function from a module, there is a shortcut!

from module import function

Import part 2

Typing 'from math import sqrt' allows us to use the sqrt function without constantly typing math. We can only use the

sqrt function though.

Super lazy!Is there a way to import every function from a module? Yep!

from module import *

Now we can use everything without having to type the module name in front.

WarningBe careful about universal imports. Some modules have a lot

of functions in them, so there is a risk you will try to define your own function of the same name. This will cause issues.

!Stick with importing individual functions or using

module.function()

Built-in functions

Python has some built in functions that we can use without importing anything. We've seen a few already with strings: len,

lower, and upper.

max()

If you give max a list of numbers it will return the maximum value.

min()If you give min a list of numbers it will return the minimum

value.

abs()abs() returns the absolute value of a function.

type()Not quite as simple- type() returns the type of the argument

you gave it.

What we did today• Functions!

• Defining

• Arguments

• Imports

• Built-in