10. Debugging code

Debugging code is always a very important part of the development process. In this section, we shall try to give a quick look on how to do it.

10.1. Post-morten

To debug code once an exception is raised, you can call:

%debug

You can also toggle automatic postmorten debug with:

%pdb

Or by starting ipython with the --pdb option (i.e. ipython --pdb). This way whenever an exception is raised the debugger will be started automatically.

10.2. Easy breakpoint

To start the debugger at an specific point in a Python code, you can insert the following inside (a function, for example):

import ipdb
ipdb.set_trace()

Example:

def func(x):
    y = x**2
    import ipdb
    ipdb.set_trace()
    return y

10.3. Start debugging on the current terminal

You can also start debugging on the current terminal by using:

import ipdb
ipdb.set_trace("", locals(), globals())

10.4. Debugger commands

There are many command you can run inside a debugger, other than just python code, the most important being:

  • d(own): d or down go down in the context.

  • u(p): u or up go up in the context.

  • s(tep): executes the current line and stops, but if the line is itself another function, the it go inside it. n(ext) on the other hand always goes to the next line.

  • l(ist): show more code around.

  • p: in general just typing a variable will allow you to see its content, but what if a variable has the same name of a command, then just append p before it, example: p next.