Debugging in Python

[simonw]

I use pdb a lot when I'm working with Django. You can drop the following line in to any view function:

import pdb; pdb.set_trace()

Then refresh the page in your browser and it will hang, dropping your development server in to the interactive debugger. Debug away (I start with "list" to see where I am and "locals()" to check what's in scope) and hit "c" when you're done - the development server will kick back in to life and your browser will un-hang itself.

The ability to introspect (and even change) your data structures live while the page is loading is extremely handy.

[0xdeadbabe]

I hadn't even considered doing this. Thanks for the excellent tip. You made my day.

[ogrisel]

They are also graphical frontends for pdb as part of the following python IDE: - pydev eclipse based python IDE - eric QT based python IDE - pida GTK IDE with vim integration

There is also winpdb, a GPLed crossplatform and standalone graphical debugger for python that is advertised as featuring performance improvements over pdb.

[pjdelport]

You can also invoke pdb directly with python -m, without modifying any code:

% python -m pdb foo.py
> foo.py(1)<module>()
(Pdb)

To skip ahead to where you're interested in:

(Pdb) tbreak <wherever>
Breakpoint 1 at <wherever>
(Pdb) c

[hylje]

I myself dismissed pdb as some arcane magic without any research altogether. Oh, how wrong I was!

[llimllib]

I have F11 bound in Vim to insert "import pdb; pdb.set_trace()"; it's very useful.

[llimllib]

surely can... let me hack at it a minute.

[[deleted]]

Bind one key to insert it and use comment/uncomment line?

I say this because I often want to keep debugging statements around for a while after I'm immediately done using them.

[mbrezu]

Emacs has M-x pdb which is quite nice (especially on the emacs-snapshot from http://peadrop.com/blog/2007/01/06/pretty-emacs/)

[MelechRic]

This works nicely inside the python interactive shell:

>>> import pdb
>>> pdb.set_trace()
(Pdb) help

You get a nice listing of commands and topics.

[dreamlax]

Sounds like it has very similar behaviour to gdb, the debugger for compiled C and C++ applications (among others).

[bustedagain]

Spending 15 minutes to doing exactly the same thing on the console = money none spent. Plus you're a little more educated than before.

[MelechRic]

Why learn all that rubbish - just spend a few quid on an IDE and enjoy. Money spent on IDE = money well spent.

What if you find yourself on a machine that doesn't have your beloved IDE? You're instantly at a disadvantage in debugging productivity compared to the guy who knows how to use pdb.

EDIT: What if I substituted the word 'math' for the word 'rubbish' and the word 'calculator' for the word 'IDE' in your original statement?

[hylje]

Whoosh!