How can I start the python console within a program (for easy debugging)?

Question

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!

Answer 1

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]:

• Yuji 'Tomita' Tomita: Hey, nice iPython! Gotta give that a try.

Answer 2

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"

Answer 3

The code module contains classes for bringing up a REPL.

• Ankit Jaiswal: Interesting, I did not know about it. I will give it a try.

Answer 4

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!)

Answer 5

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

Answer 6

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