Summary of Unit 1: Programming Basics

This is a summary of the topics covered in Unit 1: Programming Basics.

When you have received the topics, try some of the challenges at the very bottom of this document.

Printing

The print() statement is a function that outputs text to the screen. Some notes on its usage:

• String literals should be enclosed in quotes, e.g. print("Hello, world!")
• Variables can be output, without quotes, e.g. print(user_name)
• Strings can be concatenated or combined using a print statement. Both + and , can be used to concatenate strings, with slight differences:
  • Plus (+): The + operator only works with strings data types. If you are printing integers or floats using +, you must convert these to strings with a function like str(). For example:
    • print("Hello, " + user_name + "!")
    • print("Total Price: $" + str(total_price))
  • Comma (,): The , operator automatically converts non-string arguments to strings before printing, however, it automatically adds a space between the elements being printed. For example:
    • print("Total Price:", total_price)
    • print("Name:", user_name, "Age:", num_user_age)

Variables

A variable is something that stores information in a program so that it can be used later.

Variable Types

We've looked at several different types of variables in Python:

Type	Short Form	Definition	Examples
String	str	A sequence of characters, enclosed within quotes	"hello", 'world'
Integer	int	A whole number without a decimal point	5, 100, -42
Float	float	A number with a decimal point	3.14, -0.5, 2.0

Variable Assignment Statement

A variable is created and updated using an assignment statement:

Determining Type

You can use the type function in Python to determine a variable's type. For example:

Code

greeting = "Hello, world!"
pritn(type(greeting))

Output

<class 'str'>

In addition, it is good programming practice to be strict about maintaing consistency with your variables and data types. Try to avoid using the same variable for strings and integers at different points in your program.

Best Practices with Variable Naming

It's important to follow good variable naming conventions and style guidelines (outlined in a document called the Python Enhancement Proposal 8, or PEP8). This helps us write clean, readable, and maintainable code.

Here are some good beginner variable rules based on PEP8:

Use descriptive names

Choose variable names that are meaningful and describe their purpose or content. Avoid single-letter variable names except for loop indices or other very short-lived variables.

Good

name = "John"
num_students = 10

Bad

n = "John"
x = 10

Use lowercase letters with underscores for multi-word names (i.e. snake_case)

Use underscores (_) to separate words in variable names for better readability.

Good

max_speed = 100
user_name = "example"

Bad

MaxSpeed = 100
userName = "example"

Avoid using reserved words

Do not use special or reserved words as variable names.

Bad - 'class' is a reserved word

class = "example"

Be consistent

Maintain consistent naming conventions throughout your codebase.

Good

max_speed = 100
min_speed = 50

Bad

maxSpeed = 100
min_speed = 50

Use meaningful prefixes for variable names in specific contexts

Use prefixes such as "is_" for Boolean variables, "num_" for counts or number variables, and "str_" for string variables.

Good

is_valid = True
num_students = 10
str_name = "John"

Bad

valid = True
students = 10
name = "John"

Avoid magic numbers

Assign numbers to variables with descriptive names instead of using them directly in your code.

Good

max_speed = 100
acceleration = 9.8

Bad

distance = time * 9.8

User Input

Use the input() function in Python to retrieve text from a user. Note that all input comes as the string data type. You can nuse type conversion to change a variable's type for further use.

Mathematical Operators

These are a few of the most common mathetmatical operators seen in Python:

String Operators

These are a few unique cases when using + and * operators on strings:

Adding two strings together is called concatenation and can only be done with strings. You can use type conversion (e.g. str(3.14))to make sure that all elements are strings before concatenating.

Comments

Comment Types in Python

1. Single-Line Comments:

   • Description: Single-line comments are brief comments that span only one line. They are preceded by the # symbol.

   • Usage: Use single-line comments to provide short explanations, notes, or context for specific lines of code.

   • Example:

     # This is a single-line comment
     x = 10  # This is another comment

   • Good Practice:

     • Use single-line comments to clarify complex or non-obvious code.
     • Place comments above the line they describe for clarity.

   • Try to Avoid:

     • Avoid simply replicating code in comments, which can lead to redundancy and confusion:

       num_a = 10  # num_a is 10
       num_b = 20  # num_b is 20
       
       # result is num_a + num_b
       result = num_a + num_b
       
       # print result
       print("Result:", result)

2. Multi-Line Comments:

   • Description: Multi-line comments, also known as docstrings, are used to document entire programs, functions, modules, or classes. They are enclosed within triple quotes (''' or """).

   • Usage: Multi-line comments provide detailed documentation about purpose, usage, inputs, outputs, and behavior of entire programs, functions, modules, etc.

   • Example:

     """
     File: celsius.py
     Author: Dave Cheng
     Date: 2024-02-21
     Description: Converts temperture from Celsius to Fahrenheit.
     """
     
     # Get Celsius temperature from user
     temp_celsius = float(input("Enter temperature in Celsius: "))
     
     # Convert Celsius to Fahrenheit
     temp_fahrenheit = (celsius * 9/5) + 32
     
     # Output result
     print("Temperature in Fahrenheit:", temp_fahrenheit)

   • Good Practice:

     • Use a multi-line comment as a program header to describe what a program does.
     • Use docstrings to document functions, methods, classes, and modules.
     • Follow a consistent docstring format to enhance readability and maintainability.

Best Practices with Comments

• Clarity Over Comments: Strive to write clear and understandable code. Use comments only when necessary to explain complex logic or provide additional context.
• Avoid Verbosity: Ensure that you don't have too many comments. Code that is too verbose or wordy can take away from readability and clarity.
• Consistency: Follow consistent commenting conventions throughout your codebase to improve readability and maintainability.

Practice Problems

Problem 1

Create a program collectdata.py that asks for the following information and then outputs the information back to the console. Try to follow good variable naming practice from the notes above.

• name
• age
• current mark
• has been assigned a locker

Example Run 1

Enter your name: David
Enter your age: 16
Enter your current mark: 92.3
Have you been assigned a locker (True/False)? True

Name: David
Age: 16
Current Mark: 92.3
Locker Assigned: True

Problem 2

Now, modify collectdata.py so that it prompts for a first name and last name, but outputs the data as one:

Example Run 2

Enter your first name: David
Enter your last name: Cheng
Enter your age: 16
Enter your current mark: 92.3
Have you been assigned a locker (True/False)? True

Name: David Cheng
Age: 16
Current Mark: 92.3
Locker Assigned: True

Problem 3

Going to a restaurant in a large group can be a complicated experience, particularly when it comes to splitting the bill.

Write a program billsplitter.py that calculates how much each person should pay based on a group meal's total bill after-tax. Ask the user for input (size of group, total bill, desired tip) and output the amount each person should pay.

1. Remember, the after-tax total includes the 13 percent HST.
2. The calculated tip should not be based on the after-tax total, but rather, the pre-tax total. In other words, a 15% tip on a total bill of $113.00 should be $15 (15% of $100 pre-tax bill).
3. Dollar amounts are not integers (whole numbers) so you cannot use int(). They have decimal places. This data type is called a floating point number, or float(). You will need to convert the user's string input to floating point in order to be able to do decimal math with it.

Example Runtime

Here is a working example:

Restaurant Bill Splitter

How many people in your group? 5
What was the total bill after tax? 226
How much do you want to tip (standard is 15%)? 15

Each person should pay $51.20

Another example:

Restaurant Bill Splitter

How many people in your group? 3
What was the total bill after tax? 123.45
How much do you want to tip (standard is 15%)? 20

Each person should pay $48.43

One last set of numbers:

Restaurant Bill Splitter

How many people in your group? 8
What was the total bill after tax? 345.67
How much do you want to tip (standard is 15%)? 20

Each person should pay $50.86