Functions pt 2

CSCI100: Intro to computer science

Announcements and Reminders

• Lab 4 is due on Friday, October 4th @ 11:59pm

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• The second Google Careers in Tech Chat is this Thursday @ 6pm (again virtual, link on the course website).
• This week’s topic is on Product/Project Management!
• Lecture on Monday (10/7) will be virtual. Be on the lookout for the zoom link on the course website

• Previous Lesson Review

A little more on functions

Remember that functions are reusable blocks of code

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• With functions, code becomes a lot more readable
• They allow us to break complex code to more manageable chunks
• They can reduce errors too
• Since functions are reusable, we lessen the chance of introducing errors by duplicating code
• They save time and effort
• Since we can use blocks of code multiple times, we don’t need to write them multiple times

Return Values

• Not only can functions do a task, it can also give us the result of said task.
• This is known as returning a value
• The returned value can be stored in a variable for later use, or be printed out
• You can return anything, from strings, to integers, to even nothing (aka None!)
• To make a return statement, simply have the the word return followed by whatever you want to return (you can also have nothing after return, which will just return None)

def function_name():# function definition

# some code

return # something or nothing

Let’s look at the addition example we had Monday

Create a function that asks the user to enter two numbers, then adds the two numbers together

If I were to print the function call, it would print None because the function doesn’t return anything. How can I return the sum instead of printing it?

Return Values

• When a function reaches a return statement, the function stops (think of it like a break statement, but for functions). Any code that comes after a return statement won’t be ran
• You can only return ONE value.

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Let’s do a little practice

Write a function that takes in a the length and width of a 4-sided polygon.

If it is a square, return the area. If it’s a rectangle, return the perimeter

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EX: length: 6, width: 10, result: 32

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Now it’s your turn to practice!

• Break into to groups of 2. Feel free to grab some scratch paper
• Take a look at the following problem:
• Write a function called is_harshad that takes in an integer and returns whether or not it’s a Harshad number. A Harshad number is any number that is divisible by the sum of its digits. Return True if so, and False if not
• Ex: is_harshad(21) → True
• Ex: s_harshad(672) → False
• WITHOUT WRITING ANY CODE, work with your partner to see how you can go about solving the problem step by step
• Some questions to consider:
• How can I get the individual digits in a number?
• Hint: remember we can’t iterate through

Integers, so how can we work around that?

• What are some shorter examples I can start with?
• Are there edge cases I should consider?

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Now it’s your turn to practice!

• Now that you have an algorithm, have one person be the driver (the one writing the code) and one person be the navigator (telling the person what to write)
• Write your program in ps1.py in the Functions notebook in Codio
• Make sure you test your code periodically in the terminal!!!
• Remember you can look up syntax or ask me. I’ll come around to check on you!

Scope

• Understanding scope is extremely important in writing functions and understanding control flow
• The scope of a variable is where a variable is created and can be used.
• Write the following program on your computer and run it. What happens?

Scope

• It’ gives an error! This is because a variable created within a function only exists within the function.
• Because of that, variables created within the scope of a function can only be used in that same scope
• This is known as local scope

Scope

• Variables can also be created globally and we’ve actually been creating global variables the entire time!
• Global variables are any variables created within the main body of a python file

Scope

• Generally, creating global variables that can be used within functions is not recommended.
• In larger programs, it can make code unpredictable and harder to test.
• However there are cases where global variables are used, such as:
• Creating constants (data that cannot be changed throughout the program)
• Creating configurations that exist throughout the program
• Sharing data across multiple aspects of the program
• Still, there are better ways to achieve these goals without using global variables, so again, not recommended!

See you tomorrow! And continue practicing!