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Name: [002] Ian Ozsvald
Member: 128 months
Authored: 181 videos
Description: I am the co-founder of ShowMeDo (see, author of `The Screencasting Handbook <>`_ and the founder of the professional screencast production company `ProCasts <>`_: .. image:: ...

Interactive debugging using PyDev [ID:142] (8/10)

in series: Python Development on XP

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Debugging skills are key to making your programs work properly. Here I show you how to step through our previous in PyDev's graphical debugger, watching how the variables are created and changed, seeing how the stack changes and using breakpoints for control.

When debugging we need PyDev's debug-perspective, we launch using F11 and then Step Into and Over lines of code and watch how things evolve on the stack and variable list (hint: their colour changes). At the end of the video I show you how to switch back to the normal editing perspective from the debug perspective.

By the end of the video you'll be comfortable with PyDev's debugger and you will be able to step into and around your own code. This will give you more power in understanding how your program is running and what's going on 'under the hood'.

I mention the Change Value/Set Value menu option in the video (when debugging, in the Variables tab) - I have confirmed with Fabio (the author) that this feature is not implemented in the current version of PyDev (let Fabio know that you saw it here and ask for it to be supported!)

For more on debugging with Python (using the stock pdb, not PyDev) see Interactive Debugging in Python by Jeremy Jones.

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Hi, thanks for all good explanations. :-)

However, I can't find the code examples you are referring to in the end of the video. Please supply a link.

Excellent series, I have already learned a great deal and just getting started. Years ago I attempted to learn Python from a book, but progress was slow, and Python was not a requirement for my job, so it was put on the back burner. This past week I was speaking with a friend about how he learns programming languages and he suggested some of the sites he uses, (non-Python related). After doing some browsing, I decided to see what may be available for Python and stumbled upon your training videos. I was hooked by the second video. Of the videos I have seen, yours are more professional in appearance, focused, and to the point.

While I thought the book I was using was good, your videos show much more with regards to using the tools and other useful links. For instance the book I used , circa 2006, the index referenced ‘debugging’ for less than 10 pages, with no mention of PyDev or the Eclipse editor. In fact it states the 'string format operator' is a useful debugging tool, while that may be true, what I have just learned in this video is far superior.

Thank you.

I haven't used / seen a debugger. That was informative. Thanks.

Excellent job with this! The debugger really show's how things work in an interesting way.

Great video, love Eclipse it is really is a friendly environment to work in :- )

Review of Interactive debugging using PyDev

I seen somewhere that there are more debugging options (e.g. break when a value or expression is a certain value) available in Eclipse. Also, I believe, that you can write statements in the display window but I don't know how to do this.

It would have been nice if you had covered debugging in greater depth as it would have saved me a lot of time.

Review of Interactive debugging using PyDev

I'm new to both Python and debugging and your video has saved me a lot of time and effort.

Thank you!

This was great. I think you'd be surprised how many people don't really know how to use an IDE. I'm one of them. They're pretty intimidating to try and teach yourself...there's lots of buttons and widgets and windows. I've written 1000's of lines of C++ code, but unfortunately I was stuck using a text editor and a compiler. Eclipse could have helped me out greatly if I could have figured out how to use it. This will certainly help me a lot!

Thanks man! Helping me learn more about coding in python swiftly.


I learned a lot in this module. I am a real newbie to python (my previous programming was in Commodore Basic about 30 years ago), so graphical debugging tools seem like magic to me. I am enjoying the vids, but I think I need to do some practical programming to learn the techniques.

I would like to see a series that makes a practical application (like a check register that automatically balances the account, or something like that) from start to finish, demonstrating different techniques, error trapping, etc.

Really really useful! I have been coding PHP for 5 years and have never used a graphical debugger so this was gold dust to me! Many thanks this will make my life so much easier.

As an introduction it was great and very easy to understand, I would love some more tips on this.

great to see Pydev debugger in action.

Hi Richard - thanks for the detailed message. Fabio seems to have introduced this new dependency. Currently PyDev is at 1.3.14 and I recorded these with PyDev 1.2.5 over a year ago.

This fix is easy to implement and it won't stop anyone from using PyDev - the addition of psyco is optional.



If you are using the latest version of PyDev you will be getting to messages when starting the debugger:

when using the debug in PyDev I am not getting

exactly the message I am suppose to receive, here is the message :

pydev debugger: warning: psyco not available for debugger speedups

pydev debugger: starting

psyco can now be used by PyDev, it is improving the speed.

See link :

You can alose download psyco (with a window installer) at the following link :

After being installed it will remove the warning.

When defining the method it does ask you to confirm where to put it : at the beginning, etc.

Also it is showing you the changes it will be performing.

Great tuto.


thanks it is great helps

Good episode. Always good to have a nice, debugger. Certainly quicker than manual print stmts; I haven't used pdb, but this looks much more fun. Though I'll have to play with pydev to get over feeling nervous that I'll screw something up. But Ian nicely pointed out many things in the environment which can be safely ignored at this point.

Oh, re. whether or not pressing F11 immediately executes...apparently when Console window has focus, this occurs. When editor window has focus, F11 or run brings up selection list where you must choose python run.

Another very informative and well structured episode which I particularly enjoyed.

As debugging is a type of fault finding and rectification it really helps develop a thorough understanding of whats going on.

Fantastic, I think I'm addicted!

Miracle's syntax change worked for me for changing the values of integers, strings, and lists with one member, but not for lists with more than one member.

Cool, thanks for telling me that. Fabio (PyDev's author) had told me that he had fixed the change-variable feature but I didn't know about the new syntax.

It is so good to hear that you find the entire set to be so helpful :-) I find this really encouraging and it makes me keen to work on my next series!


Again, great episode of using Eclipse+Pydev.

The change variable feature works in the latest Eclipse(3.2.2)+Pydev(1.2.9). There is trick though: the default display is "list: [12,123,42]", you have to change it to "[12,123,42]" or other values in this format. This will work. Same for "int: 3" -> "3"

Great work! totally gets me hooked...

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Kudos and Thanks for Ian

3 Minute Oveview (What Does Python Look Like?)

simple and informative. you draw me in
70 months ago


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