Python mode in Emacs: No such file or directory, pdb

Question

I have a python script that I want to debug with python-mode. I read in this thread that I can debug my python script with M-x pdb, however I get the following error:

Searching for program: no such file or directory, pdb

I can provide python -m pdb my_source_file.py in the prompt in the minibuffer, but it would be nice if Emacs could infer this command directly from the file on which I run M-x pdb

Update:

Running on:

• Red Hat Enterprise Linux Server release 5.1 (Tikanga)
• Emacs 23.3.1

Differences between paths

I get different paths when I run M-: exec-path and when I run M-: (getenv "PATH") (the one returned by M-: (getenv "PATH") is longer).

With this:

• Where is pdb located? How can I add it to the Emacs path?
• Is there a way to ask Emacs to also look into the paths held by the environment variable PATH?

Answer 1

Further to my comment earlier, and your subsequent update to the question:

First figure out a value for $PATH that works in your terminal. Use which pdb to find where the pdb executable is located.

Then, set the $PATH environment variable explicitly in Emacs, and sync it to exec-path as follows:

(setenv "PATH" "/usr/local/bin:/usr/bin:/bin:/some/other/dir")
(setq exec-path (split-string (getenv "PATH") path-separator))

It's possible you would need to also explicitly set PYTHONPATH or similar environment variables; you can do that using lines like the "setenv" line above, or just use the exec-path-from-shell elisp package.

Update

Okay, so it turns out Emacs' pdb command isn't provided by python-mode, and it expects to find an executable called "pdb". The easy way to fix this, then is to create a shell wrapper called "pdb", in a directory on your $PATH:

#!/bin/sh
exec python -m pdb "$@"

(I found a note here suggesting this technique.)

The equivalent under Windows would be a file called pdb.bat, containing:

python -u -m pdb %1

(The -u prevents Python from buffering its output.)

Answer 2

To run the Python Debugger, M-x pdb expects to find an executable named pdb. While the pdb executable may exist in some Python distributions, it doesn't exist in all of them.

A proposal to fix this is in GNU bug report #21521: pdb default suggested command.

Until the bug is fixed, you can set the variable gud-pdb-command-name to define the command used to launch pdb. In .emacs, add...

(setq gud-pdb-command-name "python -m pdb")