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Debugging Python Like a Boss

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Re: Debugging Python Like a Boss

#31

Post by haberman »

ufo wrote: post #25
haberman wrote: post #12

Debuggers are cool and often necessary, but I disagree with this often-expressed sentiment that print-debugging is a primitive hack for people who don't know any better. Debugging is determining the point at which the program's expected behavior diverges from its actual behavior. You often don't know where where/when this is happening. Print-debugging can give you a transcript of the program's execution, which you ca…

One neat trick that I really like for ptrintf debugging is using conditional breakpoints and putting the call to the printing function inside the breakpoint condition. This lets you add print statements without editing the original code and makes it very easy to toggle them on and off.

Clever -- I've never heard or thought of that!

When I read about this more, it sounds like you can make watchpoints conditional too. You could use this pattern to print a transcript of every change that happens to a data value! Though I'm not sure if the watchpoint condition has easy access to the source file/line, so it might not be easy to log what code was changing the value.

Re: Debugging Python Like a Boss

#32

Post by hcarvalhoalves »

gknoy wrote: post #19
hcarvalhoalves wrote: post #3

A good list of libraries, but please, don't use this in the middle of your code to set a break point: import pdb; pdb.set_trace(); There's a chance you forget this, check-in, and it ends in production. Use pdb facilities instead: $ python -m pdb Then set a breakpoint and continue: (Pdb) break : (Pdb) c This is trivial to automate from any editor or command line, so you don't even have to guess the path to the file. E…

We avoid that by having a build step fail if 'import pdb' exists in our codebase. You could do similar for any of these tools. This will then lead to build failures in one's automated build system, and flag pull requests as not-yet-ready to be merged with our master branch. If one doesn't have an automated test process, then I suspect one has bigger potential errors that could sneak in than an errant pdb breakpoint.…

Sure, that's beautiful in theory. But you have to remember to catch the strings "import pdb", "import ipdb", "import pydbgr", and the variations "from pdb import Pdb", "__import__('pdb')", all the permutations, and so on. Anyway, that's besides point.

Having to change the source to fire the debugger is a dumb way of debugging after all, and doesn't allow certain things (e.g., step thru a 3rd party library). Better coach the developers on how to use the tools properly.

Re: Debugging Python Like a Boss

#33

Post by dima55 »

edwinnathaniel wrote: post #6

I've been using Python for a while for fun and Ruby (Rails) on and off. I've always find it interesting how the Python/Ruby community debug your code both during development (coding or writing unit-tests) and perhaps in production as well (for the record, I use "print" as my debugging tool). I'm a long time Eclipse user who has recently converted to IntelliJ (almost a year) and the debugger that comes with these edit…

The emacs debugger infrastructure (gud) is pretty great, and is common for a multitude of languages. Add on top of this other fancy pants emacs features (for instance remote anything, including debugging via TRAMP) and emacs users do better than most.

Re: Debugging Python Like a Boss

#34

Post by emidln »

mcpherson wrote: post #5

While in the subject of debugging Python you should look into Bugjar (gui) http://pybee.org/bugjar/ . Looks really good.

I see pdb++[1] getting mentioned (pip instal pdbpp), and I'll also throw in wdb[2], which is a WSGI middleware that uses jedi for code introspection.

[1] - https://bitbucket.org/antocuni/pdb/src

[2] - https://github.com/Kozea/wdb

Re: Debugging Python Like a Boss

#35

Post by roycehaynes »

First off, great post Cooksey. I'm actually a sublime and pycharm type of guy, where I use pycharm mostly for debugging purposes. I use pdb only if I'm debugging on a machine thats not mine, I need to debug something fairly quickly, or PyCharm isn't available. I definitely need to give ipdb a try.

Re: Debugging Python Like a Boss

#36

Post by hcarvalhoalves »

haberman wrote: post #12

Debuggers are cool and often necessary, but I disagree with this often-expressed sentiment that print-debugging is a primitive hack for people who don't know any better. Debugging is determining the point at which the program's expected behavior diverges from its actual behavior. You often don't know where where/when this is happening. Print-debugging can give you a transcript of the program's execution, which you ca…

I only use "print debugging" (using the logging facilities more often than not) if it's something I can leave in the codebase, like logging a function call and it's parameters, or when a routine is being skipped; then a debugger if I want to check the interface or docstring of some object or retry a call with different parameters on the REPL.

Re: Debugging Python Like a Boss

#37

Post by existencebox »

evanspa wrote: post #24
haberman wrote: post #12

Debuggers are cool and often necessary, but I disagree with this often-expressed sentiment that print-debugging is a primitive hack for people who don't know any better. Debugging is determining the point at which the program's expected behavior diverges from its actual behavior. You often don't know where where/when this is happening. Print-debugging can give you a transcript of the program's execution, which you ca…

I agree. That, coupled with keeping your functions small (doing 1 thing) and tight, and being disciplined at writing unit tests can go a LONG way when it comes to debugging with simple print statements. Normally I'm able to hone in bugs with a few strategically placed prints, and a re-run of the unit tests. Pouring over stdout log is usually trivial with an incremental search, and the print statement prefixed with so…

By "unique chars" I assume you mean things like "FML" "WHYISNTTHISWORKING" "SHOULDNTBESEEINGTHIS" and the ever useful "--------------------------------------------->"

Re: Debugging Python Like a Boss

#39

Post by cgh »

edwinnathaniel wrote: post #6

I've been using Python for a while for fun and Ruby (Rails) on and off. I've always find it interesting how the Python/Ruby community debug your code both during development (coding or writing unit-tests) and perhaps in production as well (for the record, I use "print" as my debugging tool). I'm a long time Eclipse user who has recently converted to IntelliJ (almost a year) and the debugger that comes with these edit…

Yes, the ability to connect to and debug a remote, running JVM is a killer feature. And it is well supported by IntelliJ and Eclipse. But it's a function of the JVM and not the debuggers themselves - if the Python runtime offered remote debugging then I'm sure Python debuggers would support it too.

Re: Debugging Python Like a Boss

#40

Post by brian_cooksey »

roycehaynes wrote: post #35

First off, great post Cooksey. I'm actually a sublime and pycharm type of guy, where I use pycharm mostly for debugging purposes. I use pdb only if I'm debugging on a machine thats not mine, I need to debug something fairly quickly, or PyCharm isn't available. I definitely need to give ipdb a try.

Thanks, and long time no see. Hope things are going well for ya!

I'm interested in the number of people that do the Editor-of-Choice and PyCharm combo. May have to see how the GVIM PyCharm combo would work.

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