Using the Python Debugger (pdb)

Interrupting program execution

You can interrupt the program execution and start the debugger by inserting these commands at any point:

import pdb
pdb.set_trace()

The debugger shows a shell that works like the normal Python command line, but with some extra commands:

• n (next) – execute next statement.
• s (step) – execute next statement, and descend into functions.
• l (list) – show source code.
• c (continue) – continue execution until the next breakpoint.
• help – print help message.
• q (quit) – abort the program.

Breakpoints

• The command 'b <line number>' sets a breakpoint at the given line
• The command 'b' displays all breakpoints set

Tips

• A valuable diagnostic tool is to use the debugger for manipulate variable values. e.g.:

>>> a = 1

• Most IDE's are supporting the debugger. It is much more comfortable to control the program from there.
• In the debugger command line you can get help on any command by typing 'help <command>'.