Abstraction and Programming Practice

CS 110

Reminders and Announcements

• Ex 1 due tonight (very similar to Tutorial but with more specific instructions)
• Don't forget about edSTEM! (But don't use it as a last-minute lifeline)
• You can re-submit up to 10 times - the latest submission is considered the "official" one
• If you're watching the recording, make sure to complete MQ 2 by Sunday at 11:59pm
• If you're here in class follow the MQ instructions and you'll receive credit around noon today
• All submitted work is graded - if you don't have a grade for the Tutorial but you attended, see the pinned post on edSTEM.

Next Week

• Monday - MLK Jr. Day - NO CLASS
• Wednesday - Graphics Functions (Pre-Recorded + MQ 3) + Tutorial 2
• Friday - Programming Practices + MQ 4 (Exercise 2 due)

Naming Variables: Case Sensitivity

Python is case-sensitive.

Consider the following code: https://goo.gl/PJQana

x = 1

x = 2

X = 5

Y = 2

Y = 5

y = 7

3

Naming Variables: Class Conventions

Although Python doesn’t care what you name your variables (beyond the rules specified in the previous slide), there are some conventions that most people follow:�

• Ensure your variable names are mnemonic
• “Snake case” for functions and variable names
• first_name = 'Beyonce'
• last_name = 'Knowles'
• “Snake case” for file names too: hello_world.py

4

Source: https://realpython.com/python-variables/

Writing programs that mean something (mnemonic)

x = 65�y = 3�z = x * y�print(z)

rate = 65�time = 3�distance = rate * time�print(distance)

5

Functions

Blocks of code encased inside a function name

Dealing with inputs to functions

Positional parameters

• Positional parameters are non-optional (required)
• The order in which they are passed matters

Keyword parameters

• Keyword parameters are always optional and are always specified by their keyword
• They are always passed into a function after the positional parameters, but the order of keyword parameters doesn’t matter.
• Keyword parameters always have a default value

Calling Functions - Summary

print("Go", "Wildcats", sep="", end="!!!\n")

Function name

Positional (non-optional) Arguments

Keyword (Optional) Arguments

• Function calls always consist of the function name and a set of parentheses.
• Inside the parentheses go any inputs to the function. If there are multiple inputs, we separate them with a comma.

Turtles!

# Consider the following program:

left_turn(fred, 45)

forward(fred, 100)

left_turn(fred, 90)

forward(fred, 100)

left_turn(fred, 90)

forward(fred, 100)

left_turn(fred, 90)

forward(fred, 100)

​

​

Note: all of these are in the lecture files for today if you'd like to run them in IDLE

9

Turtles!

# Consider the following program:

left_turn(fred, 45)

forward(fred, 100)

left_turn(fred, 90)

forward(fred, 100)

left_turn(fred, 90)

forward(fred, 100)

left_turn(fred, 90)

forward(fred, 100)

​

​

Let's modify this code to take in a side length from the user typing something in!

10

Calling Functions - Summary

result = input("What is your name? ")

Variable to store the reported data into

• Some functions are reporter functions that return a value. If a function is reporting some data back to us, we usually want to store it in a variable so we can access that data later
• Not all functions are reporters. For example, let's see if the print function reports any data back to us…

Recall: The Big Ideas with Functions...

• Functions are a way of encapsulating, organizing, and reusing code
• They help us “abstract” away complexity and allow you to reason about your code at a higher level:
• You may not want to know exactly what steps the turtle will take to make the square…you just want to know that it CAN.
• They allow you to perform the same operations on different data values — also called arguments.

12

def name_of_function():

statement 1

statement 2…

13

A function with no inputs

For every single input (or parameter) our function accepts, we will define a variable for the function to use to store that input.

​

(Small vocabulary note: when we talk about what inputs a function accepts, we call those inputs parameters but when we talk about the actual pieces of data we give the function as inputs, we call them arguments)

def name_of_function(parameters):

statement(s)

15

A function with inputs

Dealing with inputs to functions

Positional parameters

• Positional parameters are required
• The order in which they are passed matters

Keyword parameters

• Keyword parameters are always optional and are always specified by their keyword
• They are always passed into a function after the positional parameters, but the order of keyword parameters doesn’t matter.
• Keyword parameters always have a default value