Debugging is also something which once mastered can greatly enhance your
bug hunting skills. Most newcomers neglect the importance of the
Python debugger (
pdb). In this section I am going to tell you only a
few important commands. You can learn more about it from the official
Running from the command line
You can run a script from the command line using the Python debugger. Here is an example:
$ python -m pdb my_script.py
It would cause the debugger to stop the execution on the first statement it finds. This is helpful if your script is short. You can then inspect the variables and continue execution line-by-line.
Running from inside a script
You can set break points in the script itself so that you can inspect
the variables and stuff at particular points. This is possible using the
pdb.set_trace() method. Here is an example:
import pdb def make_bread(): pdb.set_trace() return "I don't have time" print(make_bread())
Try running the above script after saving it. You would enter the debugger as soon as you run it. Now it’s time to learn some of the commands of the debugger.
c: continue execution
w: shows the context of the current line it is executing.
a: print the argument list of the current function
s: Execute the current line and stop at the first possible occasion.
n: Continue execution until the next line in the current function is reached or it returns.
The difference between
step is that step stops
inside a called function, while next executes called functions at
(nearly) full speed, only stopping at the next line in the current
These are just a few commands.
pdb also supports post mortem. It is
also a really handy function. I would highly suggest you to look at the
official documentation and learn more about it.
It might seem unintuitive to use pdb.set_trace() if you are new to this. Fortunately, if you are using Python 3.7+ then you can simply use the breakpoint() [built-in function](https://docs.python.org/3/library/functions.html#breakpoint). It automatically imports pdb and calls pdb.set_trace().