Using a debugger

Python:
Using a debugger

How to:

Let’s break down using pdb, Python’s built-in debugger. Imagine a file, buggy.py, with a sneaky bug:

def add_one(number):
    result = number ++ 1
    return result

print(add_one(7))

Running this script, you expect 8, but it just throws a syntax error. It’s debugger time!

In your terminal, run:

python -m pdb buggy.py

You’ll enter the debugger, and it looks like this:

> /path_to_file/buggy.py(1)<module>()
-> def add_one(number):

Use l(ist) to see more code, n(ext) to go to the next line, or c(ontinue) to keep running the script. When you hit the error, pdb will stop and let you inspect.

After you correct number ++ 1 to number + 1, restart the debugger to test the fix. Remember, friends don’t let friends code without a net. ‘Nuff said.

Deep Dive

Back in the Dark Ages of programming (a.k.a. before integrated development environments, or IDEs, were everywhere), debuggers were often stand-alone tools you’d use outside your text editor. They came to the rescue by letting programmers inspect the state of their software at various execution points.

As of 2023, Python’s pdb isn’t the only game in town. Folks might use IDEs like PyCharm or Visual Studio Code, which have their own slick debuggers baked in. These add handy features like breakpoints that you can set with a click, rather than typing cryptic commands.

Then there’s ipdb, a pip-installable package that brings the IPython goodness to debugging. It’s like pdb on performance enhancers, with tab completion and syntax highlighting.

Debuggers also vary in their implementation. Some get up close and personal with program execution at the machine or byte code level. Others, like many high-level language debuggers, run the code in a special environment that monitors variable states and controls execution flow.

Python:Using a debugger

How to:

Deep Dive

See Also

Python:
Using a debugger