Debug django project with embedded python debugger pdb

I use sublime-text as code editor. It doesn't have a debugger, so to debug django projects i often used

print var_name

and look for output in local development server console. I use this approach today also, but sometimes it is great to run code step by step to see variables at each step.

It can be done with embedded python debugger pdb:

import pdb; pdb.set_trace()

I.e. we put this line in needed place of code, where we want so stop. It is a breakpoint. Now refresh project page in browser. When project code will reach this line, browser will hang and in console we'll see:

(Pdb)

We now inside debugger and can input commands, for example these:

  • l - (list), look the source code
  • n - (step next) step to next line without entering inside function
  • s - (step in) step inside to next line, i.e. if we are standing at function call, we'll go inside this function
  • r - (step out) step to first line after current block of code. For example, if current line is inside cycle and r is pressed, next line will be first line after this cycle.
  • c - (continue) continue until next breakpoint, i.e. until pdb.set_trace()
  • p - (print) execude python code or just show variable: p var_name

Example:

Suppose we have such a view:

view

Insert import pdb; pdb.set_trace() in needed place and run dev server, if it not already started:

view_pdb

In browser access the page, that calls this view. The page will hang:

browser_hang

In console we see (Pdb):

pdb_console

Lets look, where we now by command l:

pdb_l

Make two next steps with n:

pdb_nn

Look value of variables about and about.content:

pdb_p

Continue with c:

pdb_c

Page is shown in browser:

browser_done

Published: Nov. 18, 2012
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