I have been doing quite some Python hacking lately, especially unit testing, and I have found some “funny” bugs in a piece of code. I wanted to do some step-by-step debugging, but I did not want to manually invoke the debugger with the same environment as the unit tests, because the preparation needed for test cases is not trivial.

Then I decided to re-read the Pdb documentation, and found a super-handy feature: the set_trace() function. I short, you can insert the following snippet in almost any piece of code:

import pdb
pdb.set_trace()

…and when the execution flow call set_trace(), the debugger will take over the terminal and display the familiar (Pdb) prompt, being the environment that of the scope where set_trace() was called.