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CS 105: FUNCTIONS Max Fowler (Computer Science) - - PowerPoint PPT Presentation
CS 105: FUNCTIONS Max Fowler (Computer Science) - - PowerPoint PPT Presentation
CS 105: FUNCTIONS Max Fowler (Computer Science) https://pages.github-dev.cs.illinois.edu/cs-105/web/ June 21, 2020 Video Series Four Topics Functions in Python Functions, Codeblocks Functions in Python Parameters, Arguments
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Functions, Codeblocks
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Function motivation
Consider making a pizza Consider the most atomic form – where do we start
a pizza?
By making the sauce
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Sauce is used in multiple places TOMATO SAUCE Pasta Pizza
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https://www.delish.com/cooking/recipe- ideas/a19660462/easy-crockpot-spaghetti- recipe/
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User-defined functions
Sequence of operations for use (and REUSABLE)
elsewhere
Function definition says what the function does:
def <name>(): <body>
Function calls/invocations RUN the functions
<name>()
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Example
def get_input_and_print(): name = input("Your name?\n") print("Hello " + name + "!")
get_input_and_print()
A definition A call
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Code Blocks
Need a way to tell Python "this statements are related" Python uses indentation
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Indentation
In other prog. languages, indentation is just good style In Python, it is syntactic and semantic These three programs are all different
Text is same, white space and behavior is different
def test(): print('first') print('second') test() def test(): print('first') print('second') test() def test(): print('first') print('second') test()
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Functions vs. Methods
Methods are functions that are part of an object/type They use dot notation For example:
my_list = [0, 1, 2, 3] my_list.append(22)
Functions, in contrast:
len(my_list)
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Video Question
When writing our own function, what do we call the
code that says what the function does?
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Functions – Parameters and Arguments
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What are Parameters?
def price_calc(cost, count): # function body here … price_calc(5.5, 10)
Passing parameters is like an assignment
Arguments are bound to their respective parameter
The variables disappear when the function ends
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Parameter names are the same, but args can differ!
In PythonTutor, let's define price_calc and then try:
price_calc(5.5, 10) price_calc(8.25, 15) price_calc(2.34, 8)
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Parameter order matters!
In price_calc, what happens if we do:
price_calc(10, 5.5)
What about:
def mult_str(name, num):
print(name * num)
mult_str("Max", 3) mult_str(3, "Max")
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Video Question – What value is printed here?
def do_thing(var1): var1.append(4) var1 = [1, 2, 3] do_thing(var1) print(len(var1))
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Functions – Return Values
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Return Values
The keyword return Ends the function Replaces the function call with the returned value in the previous 'frame'
Function calls can be part of arbitrary expressions
x = sum_num(2,5) x = sum_num(2,5) + sum_num(5,5) x = sum_num(sum_num(2,2), sum_num(3,4))
All functions technically RETURN – if we do not have the keyword
return, the function returns None at the very end
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Why does None matter?
Largely, something like this on accident:
x = print("hi there!" my_list = my_list.append(5)
In these cases, the variable will become None! None can also be a 'flag' – i.e, return None if a
function "fails"
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Video Question – Does a function NEED the keyword return to return a value?
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Functions in Excel
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Functions in Excel
Excel provides many useful "built-in" functions:
E.g., SUM(), AVERAGE(), MIN()
Take arguments: cells, cell ranges Produce return values Can be part of expressions & assignments
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