CodeBlanks Logo Icon CodeBlanks
Login Register

Business logic

Write business rules with functions and conditions.

Business logic: compute the average

In this lesson you will compute the average of the grades. sum(grades) gives the total, len(grades) the count; division yields the average:

average = sum(grades) / len(grades)
print("ortalama:", average)
# ortalama: 87.0

The starting code includes the previous lessons' solutions. You will add the average calculation and print. Since grades is now [85, 90, 78, 95], the average is 87.0.

This is the fundamental way to summarise data.

Practice Compute and print the average

Write average = sum(grades) / len(grades). Then write print("ortalama:", average).

Starter code

main.py
# Grade calculator - grades list
grades = [85, 90, 78]
print(grades)
grades.append(95)
print("eklendi:", len(grades))
# compute and print the average

Sample solution

main.py
grades = [85, 90, 78]
print(grades)
grades.append(95)
print("eklendi:", len(grades))
average = sum(grades) / len(grades)
print("ortalama:", average)

Expected output

[85, 90, 78]
eklendi: 4
ortalama: 87.0

Next step: error handling

The business logic is ready — you can compute the average. But what if the grades list is empty? len([]) is zero and division by zero raises ZeroDivisionError. In the next lesson you will guard against this with try/except.

This layer will let the app handle error cases without crashing. Robust code anticipates errors and is prepared for them. Each lesson builds on top of the previous one.

Questions and answers

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

1 How is the average computed?

  • sum(grades) * len(grades)
  • sum(grades) - len(grades)
  • len(grades) / sum(grades)
  • sum(grades) / len(grades) Correct answer

Explanation: Average = total / count. sum(grades) / len(grades).

2 Match business logic

Term Meaning
sum(grades) Total
len(grades) Count
/ Division
average Result variable

3 Complete the average calculation

Question 
average = ____ / len(grades)
Answer 
average = sum(grades) / len(grades)

Explanation: sum(grades) gives the total of the grades.

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