This document discusses functions in Python. It covers defining functions, using arguments, importing functions from libraries, and some built-in functions. Key points include: - Functions are reusable blocks of code that perform specific tasks. They reduce repetition and make code easier to debug. - To define a function use def and give it a name and body, optionally including arguments in parentheses. - Functions can be called by name and optionally pass arguments. - Useful functions can be imported from libraries like math using import or from module import function. - Python has many built-in functions like max(), min(), abs(), and type() that do not require importing.

1. ACM init()
Day 4: May 12, 2015

2. From last time
• Loops!
• While loop- don't make them infinite!
• While-else
• For loops
• For-else loops exist as well

3. 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

4. Example

5. First challenge
Modify the function to find the factorial of any number the user
inputs.

6. Answer
This is review.

7. 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 ':'!

8. Function examples

9. 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.

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

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

12. Answer

13. 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!

14. Answer
We can call a function from another function!

15. 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.

16. Answer

17. 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.

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

19. 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.

20. The math library
math has a lot of functions you can use. For example:
exponent
log
sin
pi
factorial
...
https://docs.python.org/2/library/math.html

21. 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

22. 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.

23. 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.

24. Warning
Be 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()

25. 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.

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

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

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

29. type()
Not quite as simple- type() returns the type of the argument
you gave it.

30. What we did today
• Functions!
• Defining
• Arguments
• Imports
• Built-in