PDB is an interactive debugging environment for Python programs. It allows you to pause your program, look at the values of variables, and watch program execution step-by-step, so you can understand what your program is actually doing, as opposed to what you think it's doing.

Effectively using PDB is arguably the most important skill a new Python developer can learn. This talk will show novice and intermediate Python users how to use PDB to troubleshoot existing code.

• When is it reasonable to use PDB?

  • "I don't use a debugger"

  • When is it really not reasonable?

• Modes of pdb usage

  • set_trace mode, e.g. pdb.set_trace()

  • postmortem mode, e.g. python -m pdb buggy.py or pdb.pm()

  • run mode, .e.g. pdb.run('some.expression()').

• Getting help

• Shortcut aliases (c vs. continue)

• The workhorse commands (list, print, pretty-print, next, continue, step, return, until, where, up, down):

  • list: displaying code in your current execution context

  • p and pp: displaying objects

  • continue, step, return, next, return, until: execution control

  • where: showing the current location in the frame stack

  • up, down: navigating the frame stack

• Managing breakpoints (break, tbreak, ignore, enable, disable, clear):

  • break, tbreak, ignore, enable, disable, and clear: Managing breakpoints

• Lesser-used commands (args, !-prefixing, debug)

  • debug: recursive debugging

  • !-prefixing: modifying variables

  • args: printing args to the current function

  • commands: scripting pdb

• ~/.pdbrc and PDB aliases

• Debugging in the face of threads (ie. web apps).

• "Purple bags"

  • Enhanced shells: ipdb, pudb, winpdb

  • In-editor debugger integration (Wing, Eclipse PyDev, PyCharm, etc)