debugging - Python Visual Debugger

11
votes

I know there are a thousand posts on debugging in Python but I can't find what I am looking for....a visual debugger. For example:

one@localhost ~ $ cat duh.py    
import pdb
class Coordinate(object):
     pdb.set_trace()
     def __init__(self, x, y):
         self.x = x
         self.y = y
     def __repr__(self):
         return "Coord: " + str(self.__dict__)
def add(a, b):
     return Coordinate(a.x + b.x, a.y + b.y)
def sub(a, b):
    return Coordinate(a.x - b.x, a.y - b.y)

one = Coordinate(100,200)
two = Coordinate(300,200)

add(one, two)

I want to see the values actually being used. Instead of seeing def __init__(self, x, y): I would like to see def __init__(self, 100, 200):

> /home/one/duh.py(14)<module>()
-> one = Coordinate(100,200)
(Pdb) s
--Call--
> /home/one/duh.py(4)__init__()
-> def __init__(self, x, y):
(Pdb) s
> /home/one/duh.py(5)__init__()
-> self.x = x
(Pdb) s
> /home/one/duh.py(6)__init__()
-> self.y = y
(Pdb) s
--Return--
> /home/one/duh.py(6)__init__()->None
-> self.y = y

I'm totally not used being blind on what is going on inside of the interpreter and really would like to see what is going on in the internals like other scripting language debuggers (like JavaScript step-throughs).

4
pythondebugging
I believe this is the kind of thing LightTable aims to do (live in the IDE) - not sure how well it works yet. - Gareth Latty
Just a heads-up that added some info about Winpdb to my answer. (I'm not sure if it notifies you when I edit an answer.) Winpdb is an excellent free visual debugger for Python. Not sure why I'd forgotten about it when I first replied; probably because I've been spending all my time in Komodo and IDEA. :-) - Michael Geary
thonny.org - is meant for beginners and has in-built support for a debugger that is highly visual - lifebalance

4 Answers

11
votes

That pdb debugging doesn't look like fun. I can see why you don't like it.

Fortunately, there are some visual Python debuggers out there. The two that I use most often are commercial products, but they are both well worth the cost. They are Komodo IDE and IntelliJ IDEA. These are multi-language IDEs that support many other languages in addition to Python. There is also a Python-only version of IDEA called PyCharm.

There's also a great free option, Winpdb. It's easy to use: once you install and open it, use File/Launch and enter the full path to your .py file, and then you can start debugging.

Those products are all multiplatform, but if you're on Windows another free option is Microsoft's Python Tools for Visual Studio. You can install this either into the commercial Visual Studio 2015 or the free Community Edition of Visual Studio 2015.

To give you an idea, here are screenshots of your code from Winpdb, Komodo and IDEA. I stepped into the __init__ function in each:

enter image description here  

enter image description here  

enter image description here

Don't worry if you don't like the code font I used; that's just my personal setting. And of course in normal use the screen is not so cramped; I made it small to fit in a screenshot.

I highly recommend any of these visual debuggers - it's great to be able to step through your code with a single keystroke and watch the variables change as you go.

3
votes

Your current pdb.set_trace() call is happening as the class is being defined, rather than after init is called. If you move your pdb.set_trace() call inside init

import pdb
class Coordinate(object):
     def __init__(self, x, y):
          pdb.set_trace()

          self.x = x
          self.y = y
     def __repr__(self):
          return "Coord: " + str(self.__dict__)
def add(a, b):
     return Coordinate(a.x + b.x, a.y + b.y)
def sub(a, b):
     return Coordinate(a.x - b.x, a.y - b.y)

one = Coordinate(100,200)
two = Coordinate(300,200)

add(one, two)

then in pdb you can just type print x, y and get the values:

C:\Users\randlet>python duh.py
> c:\users\randlet\duh.py(6)__init__()
-> self.x = x
(Pdb) print x, y
100 200
(Pdb) c
> c:\users\randlet\duh.py(6)__init__()
-> self.x = x
(Pdb) print x, y
300 200
(Pdb) n
> c:\users\randlet\duh.py(7)__init__()
-> self.y = y
(Pdb) n
--Return--
> c:\users\randlet\duh.py(7)__init__()->None
-> self.y = y
(Pdb) n
> c:\users\randlet\duh.py(18)<module>()
-> add(one, two)
(Pdb) print one, two
Coord: {'y': 200, 'x': 100} Coord: {'y': 200, 'x': 300}
(Pdb) s
--Call--
> c:\users\randlet\duh.py(10)add()
-> def add(a, b):
(Pdb) print a, b
Coord: {'y': 200, 'x': 100} Coord: {'y': 200, 'x': 300}
(Pdb)
0
votes

I have been using (since Jan-2011) WingIDE by WingWare (I have version 4.x Pro). I only use it for debugging, it has served me well - admittedly I am not a power user. I set breakpoints, stepped line by line, etc.

0
votes

The Python Visual Debugger for Jupyter Notebooks described here could be of interest.
(Disclaimer: I'm the lead developer)