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Project design

Design the calculator skeleton.

Project: Calculator

In this 5-lesson project you'll build a calculator. Each lesson adds one piece, and by the final lesson you'll have a complete app.

You'll use what you learned before:

  • variable assignment
  • output with print
  • int and float types

You'll also learn the function (def), if and try/except structures. Ready? Let's start.

The calculator flow

The calculator works in four steps:

  1. Input: two numbers are taken.
  2. Operation: an operator is chosen (+, -, *, /).
  3. Compute: the result is found based on the operator.
  4. Output: the result is printed.

In the first lesson we'll just define two numbers and print them. The next lessons add functions and error handling.

Practice Define two numbers and print them

First piece of the calculator: assign 10 to a, assign 5 to b. Then print both with print(a, b).

Starter code

main.py
# Calculator - define two numbers

Sample solution

main.py
a = 10
b = 5
print(a, b)

Expected output

10 5

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does a calculator need first to work?

  • Two numbers and an operation Correct answer
  • A database
  • A class
  • A file

Explanation: A calculator takes two numbers and performs an operation.

2 Assign 10 to the first number

Question 
a = ____
print(a)
Answer 
a = 10
print(a)

Explanation: a = 10 assigns an integer value.

3 Match each calculator step to its description

Term Meaning
Input Two numbers are taken
Operation Operator is chosen
Compute Result is found
Output Result is printed

All lessons in Beginner

1 Python basics

  1. What is Python?
  2. REPL and print
  3. Comments
  4. Indentation blocks
  5. python -c and scripts
  6. Summary - Python basics

2 Variables

  1. Variable assignment
  2. Multiple assignment
  3. Naming variables
  4. id and type
  5. Swapping variables
  6. Summary - Variables

3 Data types

  1. int and float
  2. bool
  3. str basics
  4. None
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Membership and identity
  6. Summary - Operators

6 String basics

  1. f-string
  2. Concatenation
  3. str.format
  4. Raw strings
  5. Triple-quote
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. elif and else
  3. Nested if
  4. Truthiness
  5. Conditional expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. range
  3. The while loop
  4. break and continue
  5. Loop else
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Lists

  1. Declaring lists
  2. Index and slice
  3. List methods
  4. in and count
  5. Sorting lists
  6. Summary - Lists

11 List comprehension

  1. Comprehension basics
  2. Filtered comprehension
  3. Dict and set comprehension
  4. Nested comprehension
  5. Generator expression
  6. Summary - List comprehension

12 Tuple, set and dict

  1. Tuple
  2. Set
  3. Dict basics
  4. Dict methods
  5. Dict comprehension
  6. Summary - Tuple, set and dict

13 Functions

  1. def
  2. return
  3. Docstring
  4. Default parameters
  5. *args and **kwargs
  6. Summary - Functions

14 Function parameters

  1. Positional parameters
  2. Keyword parameters
  3. Keyword-only
  4. Positional-only
  5. Type hints basics
  6. Summary - Function parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string methods

  1. split and join
  2. strip, lstrip, rstrip
  3. replace
  4. find and index
  5. startswith, endswith
  6. Summary - Advanced strings

17 Input and output

  1. input()
  2. int/float conversion
  3. print parameters
  4. f-string formatting
  5. sys.argv
  6. Summary - Input and output

18 Error handling

  1. try/except
  2. else and finally
  3. raise
  4. Exception hierarchy
  5. Custom exceptions
  6. Summary - Error handling

19 Modules

  1. import
  2. from import
  3. as alias
  4. __name__ == '__main__'
  5. Standard library
  6. Summary - Modules

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together