How to debug in Django, the good way?

2018-06-11 02:55:51

So, I started learning to code in Python and later Django. The first times it was hard looking at tracebacks and actually figure out what I did wrong and where the syntax error was. Some time has passed now and some way along the way, I guess I got a routine in debugging my Django code. As this was done early in my coding experience, I sat down and wondered if how I was doing this was ineffective and could be done faster. I usually manage to find and correct the bugs in my code, but I wonder if I should be doing it faster?

I usually just use the debug info Django gives when enabled. When things do end up as I thought it would, I break the code flow a lot with a syntax error, and look at the variables at that point in the flow to figure out, where the code does something other than what I wanted.

But can this be improved? Are there some good tools or better ways to debug your Django code?

There are a bunch of ways to do it, but the most straightforward is to simply use the Python debugger. Just add following line in to a Django view function:

import pdb; pdb.set_trace()

If you try to load that page in your browser, the browser will hang and you get a prompt to carry on debugging on actual executing code.

However there are other options (I am not recommending them):

* return HttpResponse({variable to inspect})

* print {variable to inspect}

* raise Exception({variable to inspect})

But the Python Debugger (pdb) is highly recommended for all types of Python code. If you are already into pdb, you'd also want to have a look at IPDB that uses ipython for debugging.

Some more useful extension to pdb are

pdb++ , suggested by Antash.

pudb , suggested by PatDuJour.

Using the Python debugger in Django , suggested by Seafangs.

I really like Werkzeug's interactive debugger. It's similar to Django's debug page, except that you get an interactive shell on every level of the traceback. If you use the django-extensions, you get a runserver_plus managment command which starts the development server and gives you Werkzeug's debugger on exceptions.

Of course, you should only run this locally, as it gives anyone with a browser the rights to execute arbitrary python code in the context of the server.

A little quickie for template tags:

@register.filter 
def pdb(element):
    import pdb; pdb.set_trace()
    return element

Now, inside a template you can do {{ template_var|pdb }} and enter a pdb session (given you're running the local devel server) where you can inspect element to your heart's content.

It's a very nice way to see what's happened to your object when it arrives at the template.

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