Debugging
- Definition: The process of identifying, isolating, and fixing errors or unexpected behavior in a program.
- Goal: Understand why the program is not working and how to fix it.
Function
- Definition: A named block of reusable code that performs a specific task. Functions take input (parameters), process it, and may return a result.
- Example:
python
def add(a, b):
return a + b
Performance
- Definition: A measure of how efficiently a program runs in terms of time (speed) and resources (memory, CPU, etc.).
- Goal: Write code that not only works but runs fast and efficiently at scale.
Write Your Programs to Facilitate Validation and Debugging
- Meaning: Structure your code so it’s easier to:
- Verify that it behaves correctly (validation)
- Trace and fix errors when things go wrong (debugging)
- Practices:
- Use functions and modules
- Write clear specifications
- Include logging or debugging output
- Use tests
Assert Statements
- Definition: Statements used to test if a condition is true during execution. If false, the program crashes with an error message.
- Purpose: Catch bugs early by verifying assumptions.
- Example:
python
assert 2 + 2 == 4 # Passes
assert 2 + 2 == 5 # Fails and raises an AssertionError
Write Specification
- Definition: A precise description of what a program or function is supposed to do, including:
- Input and output types and formats
- Expected behavior and edge cases
- Purpose: Guides development and testing.
Modularize
- Definition: Divide a program into small, manageable parts (modules or functions), each responsible for a single task.
- Benefits: Easier to understand, test, debug, and reuse.
Test Input :: Output Pair to a Specification
- Meaning: Check that for a given input, the function returns the expected output as defined by the specification.
- Example:
python
# Specification: max(x, y) returns the greater of x and y
assert max(3, 5) == 5
assert max(7, 2) == 7
Debug - Events that Led to an Error
- Definition: When debugging, trace the sequence of steps and variable values that led to a bug or error.
- Tools: Print statements, debuggers, logs, stack traces.
Testing
- Definition: Process of checking whether the program works as intended.
- Unit Testing: Validate individual components (e.g., functions, classes).
- Test small parts in isolation.
- Example: Test if a sorting function works for different kinds of lists.
Integration Testing
- Definition: Test how components work together as a complete system.
- Note: Usually done after unit testing is complete.
- Goal: Ensure the whole program behaves correctly.
Look at Something Small
- Advice: When debugging or writing code, focus on small, manageable pieces instead of the whole program.
Code Review Example
python
Edit
def max(x, y):
x & y float # This line is invalid syntax.
- Problem:
x & y float is not valid Python and doesn’t specify types correctly. - Correct version (with type hints):
python
Edit
def max(x: float, y: float) -> float:
return x if x > y else y
Billions of Options, Exhaustive Testing is Impossible
- Meaning: For many programs, there are too many input combinations to test all of them.
- Solution: Test a representative subset that covers:
- Typical cases
- Edge cases
- Error cases
Test Suite
- Definition: A collection of tests that verify different parts of a program.
- Design Goals:
- Small enough to run quickly.
- Large enough to give confidence in correctness.
