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After years of research programming in Matlab, I miss the way I could pause a program mid-execution and inspect the variables, do plotting, save/modify data, etc. via the interactive console, and then resume execution.

Is there a way to do the same thing in python?

For example:

 # ... python code ... RunInterpreter # Interactive console is displayed, so user can inspect local/global variables # User types CTRL-D to exit, and script then continues to run # ... more python code ...

This would make debugging a lot easier. Suggestions much appreciated, thanks!

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6 Answers 6

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6

Use the pdb library.

I have this line bound to <F8> in Vim:

import pdb; pdb.set_trace()

That will drop you into a pdb console.

The pdb console isn't quite the same as the standard Python console… But it will do most of the same stuff. Also, in my ~/.pdbrc, I've got:

alias i from IPython.Shell import IPShellEmbed as IPSh; IPSh(argv='')()

So that I can get into a "real" iPython shell from pdb with the i command:

(pdb) i ... In [1]:
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Hey, nice iPython! Gotta give that a try.
5

The excellent solution I found was to use the 'code' module. I can now call 'DebugKeyboard()' from anywhere in my code and the interpreter prompt will pop-up, allowing me to examine variables and run code. CTRL-D will continue the program.

import code import sys def DebugKeyboard(banner="Debugger started (CTRL-D to quit)"): # use exception trick to pick up the current frame try: raise None except: frame = sys.exc_info()[2].tb_frame.f_back # evaluate commands in current namespace namespace = frame.f_globals.copy() namespace.update(frame.f_locals) print "START DEBUG" code.interact(banner=banner, local=namespace) print "END DEBUG"
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3

The code module contains classes for bringing up a REPL.

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Interesting, I did not know about it. I will give it a try.
2

Check out the Python debugger. In short, you can insert

import pdb; pdb.set_trace()

at any point in your program that you want to debug. (Note that you should remove these in release versions!)

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1

pdb is what you're looking for - just put a call to pdb.set_trace() wherever you want to drop into an debugger.

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-1

Here is a better, simpler solution, works in Python 3.8 https://stackoverflow.com/a/1396386/4566456

Even more powerful if IPython is installed https://stackoverflow.com/a/8152484/4566456

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