debugger - pdb

Tip

Try pip install pdbpp

Links

• This is excellent: Clayton Parker - So you think you can PDB? - PyCon 2015

• Using pdb by Eric Holscher.

• Debugging in Python, gentle introduction to using pdb

• PuDB is a full-screen, console-based visual debugger for Python.

• pdb++ is a drop-in replacement for pdb (recommended by Michael Foord).

Commands

l	list	Shows the current code around the line that your on. The line that is about to be executed has a -* before it.
n	next	Executes the current line and moves to the next in the current file.
p	print
pp	pretty p	This is very good to use
c	continue	Finishes the debugging session. If there are more breakpoints (or if your set_trace() code gets called again before the request finishes) then you will get back to the debugger, otherwise the requests will complete back to the browser.
s	step	Goes down into the next level of execution (presumably a different file). You can follow your code through Django’s internals this way. This is really good for finding bugs and getting a better understanding about how Django works.
r	return	Continue execution until the end of the current function.
until		To get through a loop
w	where	Shows you a backtrace of the calls that have gotten you to the current point in the code execution. This is really handy for the following 2 commands.
u	up	Allows you to go up one level in the backtrace.
d	down	Allows you to go down one level in the backtrace. These two commands allow you to see where you came from, and what variables were called where. This lets you see how the state ended up the current way that it did, which is great for figuring out how to fix it. :)
locals()		This isn’t a debugger function, but it is really handy for seeing what is in the current scope that you can muck around with. locals().keys() is really nice too just to see the variables that are there, because request tends to pollute the locals() command.

Issues

If your screen gets corrupted running pdb, try typing one (or more) of the following:

reset
tset
stty sane

(From Fixing a misbehaving terminal after after software interruption (pdb or messed up output).

Sample

import pdb; pdb.set_trace()

Note: To invoke the full-fledged python shell anywhere in code:

import code; code.interact(local=locals())

Ctrl D on linux to continue (Ctrl Z on Windows)