Using pdb for Debugging

Debugging is an important part of writing code, and Python has a built-in tool called pdb to help with this.

What is pdb?

pdb is Python’s interactive debugger. It lets you pause your code, inspect variables, and step through the code line by line to find out what’s going wrong.

Setting Breakpoints

Breakpoints allow you to pause your code at specific points to see what’s happening at that moment.

Example:

In your Python script, you can set a breakpoint like this:

import pdb; pdb.set_trace()

def add(a, b):
    return a + b

result = add(2, 3)
print(result)

When you run this script, it will pause before returning the result, allowing you to inspect variables and step through the code.

Stepping Through Code

pdb lets you execute your code line by line to see what happens at each step.

Example:

Using the same script, once pdb pauses execution, you can step through the code.

(pdb) n  # 'n' is for next line
(pdb) p a  # 'p' is for print
2
(pdb) p b
3
(pdb) c  # 'c' is for continue

Inspecting and Modifying Variables

You can check and change the values of variables at any point during execution.

Example:

While debugging, you might find the value of a is not as expected. You can modify it.

(pdb) p a
2
(pdb) a = 5
(pdb) p a
5

Evaluating Expressions

pdb lets you run Python expressions interactively, so you can test code snippets in real-time.

Example:

(pdb) p a + b
8

Why Use pdb?

Using pdb gives you a deeper understanding of your code’s execution flow compared to just using print statements. Instead of scattering print statements throughout your code, you can use pdb to explore and diagnose issues interactively. This makes debugging more efficient and helps you find the root cause of problems more effectively.