Example
Most basic Django debugging tool is pdb, a part of Python standard library.
Init view script
Let's examine a simple views.py script:
from django.http import HttpResponse
def index(request):
foo = 1
bar = 0
bug = foo/bar
return HttpResponse("%d goes here." % bug)
Console command to run server:
python manage.py runserver
It's obvious that Django would throw a ZeroDivisionError when you try to load index page, but if we'll pretend that the bug is very deep in the code, it could get really nasty.
Setting a breakpoint
Fortunately, we can set a breakpoint to trace down that bug:
from django.http import HttpResponse
# Pdb import
import pdb
def index(request):
foo = 1
bar = 0
# This is our new breakpoint
pdb.set_trace()
bug = foo/bar
return HttpResponse("%d goes here." % bug)
Console command to run server with pdb:
python -m pdb manage.py runserver
Now on page load breakpoint will trigger (Pdb) prompt in the shell, which will also hang your browser in pending state.
Debugging with pdb shell
It's time to debug that view by interacting with script via shell:
> ../views.py(12)index()
-> bug = foo/bar
# input 'foo/bar' expression to see division results:
(Pdb) foo/bar
*** ZeroDivisionError: division by zero
# input variables names to check their values:
(Pdb) foo
1
(Pdb) bar
0
# 'bar' is a source of the problem, so if we set it's value > 0...
(Pdb) bar = 1
(Pdb) foo/bar
1.0
# exception gone, ask pdb to continue execution by typing 'c':
(Pdb) c
[03/Aug/2016 10:50:45] "GET / HTTP/1.1" 200 111
In the last line we see that our view returned an OK response and executing as it should.
To stop pdb loop, just input q in a shell.
