Absolutely, I don't understand why using print() or its equivalent in other languages is looked down upon. It's quick way to narrow down the "area of search" before bringing in the big guns.
> It's quick way to narrow down the "area of search" before bringing in the big guns.
What are the big guns? with a debugger, I can stick a breakpoint and look at the entire state of everything. Given we're talking about Python, in pycharm [0] you can even execute your print statements in the debugger if you so wish. If you get the location wrong, or want to see what's going on elsewhere you can just continue execution and use another breakpoint.
This is even more important if you have a long compile/deploy cycle (I work in games, and rebuilding and deploying to a console can be a >10 minute iteration time)
Sometimes sticking the debugger into the wheel makes stuff come flying over the handle bars in spectacular ways that have nothing to do with what you wish to observe. You might not even know which wheel to jam the debugger stick into, if the behaviour is complex.
In these cases prints work well as a less intrusive way to get a rough idea of what is going on.
Imagine putting breakpoints in multiple tight loops in the stage of narrowing the search space. Imagine how many times you need to click next. A conditional breakpoint will only help if you know the condition you're looking for, but there's stage before that of "Well, what looks strange during execution".
Also for multithreaded code, stopping one thread dead for long enough for a human to investigate it can inadvertently resolve all sorts of race conditions.
What I imagine Macha is arguing for is that the cost of using print is extremely small, smaller at least than breakpoints.
No one is saying breakpoints are useless, sometimes printing is 'cheaper' in time and effort in order to locate the region code of code in which using breakpoints is cheaper.
Yes, print() and breakpoints are different tools with different uses and there's cases where one is superior to the other. This is why some tools now offer logpoints, which are basically print() inserted via a breakpoint UI rather than in your code where you can forget to remove them
> the cost of using print is extremely small, smaller at least than breakpoints.
I don't think it is, at all. The cost of using print is re-running your applciation with a code change, whereas the cost of a breakpoint is re-running your application with a breakpoint. Clicking in a gutter in an editor, pressing a keyboard shortcut, or typing "b <line number>" into your debugger is no more time or effort than adding a print statement, and re-running your program.
> Imagine putting breakpoints in multiple tight loops in the stage of narrowing the search space.
If you have enough loops to make breakpoints impossible to use, you've likely got enough log output that you're not going to be able to parse. You're almost certainly going to look for other ways of narrowing the search space.
> stopping one thread dead for long enough for a human to investigate it can inadvertently resolve all sorts of race conditions.
Stopping one thread for long enough to do console IO has the same effect. Especially if you're using python, you'll need a lock to synchronise the print statement across your threads!
Today I was trying to solve the exact scenario in the second example. A multi threaded program had a race condition that would sometimes occur. printing numbers helped a great deal. Might also be that I'm not that proficient with my debugger even though I use that more than anything.
> in pycharm [0] you can even execute your print statements in the debugger if you so wish
In my experience, debuggers are really good to expose hidden control flow. But usually, I know the flow, and using a debugger for human-in-the-middle print statements is just going to slow me down. Worse, those print statements are ephemeral, so I'm disinclined to write a nice formatter.
Print debugging leverages the language -- want to print in a certain condition? Easy. Have a recursive structure, an array, or a graph that you need to investigate? A naked print sucks, a custom formatter is great. Need to check some preconditions/postconditions? Do that in code. Don't try to check that stuff by hand in the debugger.
Speaking personally... the only thing I like about icecream is that ic(foo) both prints and returns foo, because you can inject it into code basically for free. But I already have a solution to that:
The same thing happens all over Software really. Just because a tool is powerful is looked up as superior, or better.
The main argument that I have seen is that in print debugging you are relying on the program being executed in a non-descriptive/non-declarative fashion.
I legitimately believe print debugging is incredibly powerful (With a simple print I can check if a function is being called, how many times, if the value has the value I expected and the only requirement I need is to be able to see the stdout of the process. I say that is fantastic!
The real world is all about cost analysis. How much value can I get from a tool vs setup and running cost. The cost of print debugging is incredibly small.
Print debugging has all of those features and is natively built into just about every programming language in existence and doesn’t require any additional libraries or tools.
> The main argument that I have seen is that in print debugging you are relying on the program being executed in a non-descriptive/non-declarative fashion.
Generally when I am coding I auto-run the tests on save. This means that to printf-debug I just add a message or two (and if I am coding I might already have a couple of useful ones lying around) and save. Then in less than a second I have a trace trough my program in the terminal. If I want to inspect a different variable I just add another print and run again.
With a debugger I need to kill my auto-run command, run the program, set breakpoints, type to see what variables I want to inspect, maybe switch stack frames, maybe step through a bit.
In my mind printf is like an automated debugger. I just put the info I want to see into the program and it does all of the printing for me. And when I find the problem I can just fix it and I am back to my edit-test cycle.
I'm not saying that there are no use cases for a debugger. For example I find variable-modification breakpoints very useful. As you mentioned if your edit-run cycle is slow then it may be faster to inspect a new variable in the debugger than adding another print statement. But when I just want to inspect values in my program I find printf sufficient and lower overhead. I'm sure part of my problem is that because I rarely use a debugger I am not as efficient, but I also think that printf-debugging is a very effective workflow for a wide variety of issues.
Every proper IDE has a keyboard shortcut for that though.
With a debugger I need to kill my auto-run command, run the program, set breakpoints, type to see what variables I want to inspect
This indeed falls under your 'part of my problem is that because I rarely use a debugger' statement. E.g you could set breakpoints before you save, use auto-debug instead (i.e. launch program under the debugger on save instead of just rnning it - without breakpoints there shouldn't be much of a difference unless it's one of those nasty multithreading bugs), add variables you want to see to the watch window. Or type them anyway if it's a one-time thing. Or use tracepoints. Etc.
I personally keep bouncing back and forth between debugger and printing. All depends on context, but it's definitely worth it getting to know both really well.
When I use a debugger I often feel like I'm looking through a soda straw. I can only see the state at that one instance in time. Just because I know the line of code where the exception occurred, doesn't tell me which data caused it, and breaking on exceptions is often too late. Instead I'm stuck hitting continue over and over until I finally see something out of place, realize I went to far and have to start over again. With logging, I have the entire history at my fingertips which I can skim or grep to quickly pinpoint the data that caused things to go wrong.
More fairly, it is a trade-off with the debugger giving wide visibility into state, but narrow visibility temporally, and logging giving narrow visibility into state (just what you logged), but broad temporal visibility. They both have their place, but I find that logging narrows things down more quickly, while the debugger helps me understand the problem by walking through step-by-step, assuming the problem isn't obvious once narrowed down.
Would be nice if instead of break points debuggers had log points which stored the values of variables at that point in time. This data can be displayed as a table later.
I more or less agree; but I find myself wondering why I so often use Matlab's debugger, but almost never use pdb for python. It is not like I'm not used to using command line tools (I use bash, git, emacs, etc. everyday). It could just be an accident of habit, I don't know.
Depending on how complex your debugger is, it allows you to output values that might not be inspectable through the debugger. Especially computed values.
Debug printing also allows you to debug programs running in environments where you can't attach a debugger. For example, maybe halting the program causes the bug not to trigger. Or it's a remote system where you cannot attach a debugger for various reasons. Or the bug only happens in the optimized build, which in say C/C++ can make it quite tedious to walk through with a debugger.
Most of the time though I use print as "proactive debugging". Having detailed logs available is gold when customer calls with a blocking issue.
You have to first configure your IDE/editor to allow you debugging. This is different for every programming language/environment. Print works in any language without prior configuration.
In the time it takes me to figure out how to connect a debugger to the process I've had a good half-dozen full loops of 1) add print statements 2) compile 3) run already done.
As opposed to software breakpoints which change your compiled binary at runtime in order to debug it. Even if you're using hardware breakpoints you're still changing what the CPU is doing and can easily make multi-threading bugs disappear.
I do it in a different branch & discard it afterwards. Having said that, I never meant print() should be used in place of a proper debugger. All I am saying is they both can complement each other and each one has its place & value. As for me, I find it quicker to add a few print statements and get a rough idea before firing up a debugger(if required). May be others are more proficient in using debuggers. But print() works for me.
Depending on the use case it can be a sign that they don't understand how to debug efficiently. Not that this is something you should judge someone for.
What are the big guns? with a debugger, I can stick a breakpoint and look at the entire state of everything. Given we're talking about Python, in pycharm [0] you can even execute your print statements in the debugger if you so wish. If you get the location wrong, or want to see what's going on elsewhere you can just continue execution and use another breakpoint.
This is even more important if you have a long compile/deploy cycle (I work in games, and rebuilding and deploying to a console can be a >10 minute iteration time)
[0] https://www.jetbrains.com/help/pycharm/part-1-debugging-pyth...