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Debugging Python with PDB

I suck at using debuggers, largely because I don’t launch them often enough.

Fortunately, this year’s PyCon had a great talk from Chris McDonough on how to get started with Python’s debugger, PDB. The friendly people at Stockholm’s Python meet-up suggested it.

I made notes while watching, to remove excuses from future me on launching pdb.

Where you want to have the debugger start, add the following code:

import pdb; pdb.set_trace()

This drops you into a PDB prompt. This is more helpful than putting in yet more print statements.

Some helpful commands once you’re in:

While in PDB, you can evaluate python code. The evaluated code won’t impact the running program.

For a bonus trick if you’re using Emacs, try out pdb track mode. Launch your python process to be debugged in an emacs shell (M-x shell). Stepping through the code in pdb will track with a source code buffer.

This worked out of the box with my emacs config. Your milage may vary.

I may actually start to enjoy debugging now!