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Python - Debugging

What is Debugging?

Debugging is the process of identifying and fixing errors (bugs) in your code. In Python, debugging tools help locate where your code goes wrong and why.

Why Debugging is Important

  • Improves code quality and reliability
  • Reduces runtime errors
  • Helps understand complex bugs
  • Essential for large-scale development

Common Debugging Methods

  • print() Statements
  • pdb - Python Debugger
  • IDE Debugging Tools (PyCharm, VSCode)
  • Logging for production-level debugging

1. Using print() Statements

Quick but not scalable. Useful for small scripts.

python 
def divide(a, b):
    print("a =", a)           # Debug print
    print("b =", b)
    return a / b

result = divide(10, 0)
print(result)

2. Using pdb (Python Debugger)

pdb is an interactive source code debugger.

python 
import pdb

def divide(a, b):
    pdb.set_trace()           # Start debugging
    return a / b

divide(10, 0)

During execution, type commands like:

  • n – next line
  • c – continue execution
  • q – quit debugger
  • p var – print value of var

3. Using Logging Instead of print()

Preferred in production environments.

python 
import logging

logging.basicConfig(level=logging.DEBUG)

def divide(a, b):
    logging.debug(f"a = {a}, b = {b}")
    return a / b

divide(10, 2)

4. Debugging in IDEs

Modern IDEs like PyCharm and VSCode have built-in debuggers that let you:

  • Set breakpoints
  • Inspect variables
  • Step through code
  • Watch expressions

5. Common Debugging Commands (pdb)

  • l – list source code
  • p – print variable
  • s – step into function
  • b lineno – set breakpoint at line
  • r – continue until return

6. Catching Exceptions

Using try-except blocks helps isolate faulty logic.

python 
try:
    result = 10 / 0
except ZeroDivisionError as e:
    print("Error:", e)

Best Practices

  • Use logging over print statements
  • Use IDE debugging for complex issues
  • Combine exception handling with logging
  • Use assertions to validate assumptions

Conclusion

Debugging is a fundamental part of development. From simple print statements to advanced IDE debuggers, Python offers flexible tools for finding and fixing errors efficiently.