How can I quit the entire program like this in Julia? (this is in Python):
import sys
def some_func():
# do something
sys.exit()
Thank you!
You do not need to import Base for exiting; you can just use exit:
function some_func()
# do something
exit() # <- you can provide exit code if you want.
end
I'll warn you that Stack Overflow is notoriously hostile to questions like these, that demonstrate that you've not attempted to research the answer to this question before coming to Stack Overflow for help. I say this only to give you a heads up about the sorts of responses that you'll normally receive on this platform, not necessarily because I think that's how it should be. When I googled "julia exit program", the answer was one of the top four results.
All that being said, here's how you do it:
import Base
Base.exit(exit_code)
...where exit_code is the number you wish to exit with. If you omit it, it defaults to zero.
Related
I was going through swirl() again as a refresher, and I've noticed that the author of swirl says the command ?matrix is the correct form to calling for a help screen. But, when I run ?matrix(), it still works? Is there a difference between having and not having a pair of parenthesis?
It's not specific to the swirl environment (about which I was entirely unaware until 5 minutes ago) That is standard for R. The help page for the ? shortcut says:
Arguments
topic
Usually, a name or character string specifying the topic for which help is sought.
Alternatively, a function call to ask for documentation on a corresponding S4 method: see the section on S4 method documentation. The calls pkg::topic and pkg:::topic are treated specially, and look for help on topic in package pkg.
It something like the second option that is being invoked with the command:
?matrix()
Since ?? is actually a different shortcut one needs to use this code to bring up that page, just as one needs to use quoted strings for help with for, if, next or any of the other reserved words in R:
?'?' # See ?Reserved
This is not based on a "fuzzy logic" search in hte help system. Using help instead of ? gets a different response:
> help("str()")
No documentation for ‘str()’ in specified packages and libraries:
you could try ‘??str()’
You can see the full code for the ? function by typing ? at the command line, but I am just showing how it starts the language level processing of the expressions given to it:
`?`
function (e1, e2)
{
if (missing(e2)) {
type <- NULL
topicExpr <- substitute(e1)
}
#further output omitted
By running matrix and in general any_function you get the source code of it.
Does Julia have an equivalent of Python's with? Maybe as a macro? This is very useful, for example, to automatically close opened files.
Use a do block. Docs on do blocks are here.
And here is an example of how to do the usual with open(filename) as my_file of Python in Julia:
open("sherlock-holmes.txt") do filehandle
for line in eachline(filehandle)
println(line)
end
end
The above example is from the Julia wikibooks too.
Although the do block syntax does have certain similarities to Python's with statement, there is no exact equivalent. This is discussed in further detail in the GitHub issue "with for deterministic destruction". The issue concludes that this structure should be added to Julia, although no syntax or plan for such is established.
Consider the following code:
File C.jl
module C
export printLength
printLength = function(arr)
println(lentgh(arr))
end
end #module
File Main.jl
using C
main = function()
arr = Array(Int64, 4)
printLength(arr)
end
main()
Let's try to execute it.
$ julia Main.jl
ERROR: lentgh not defined
in include at /usr/bin/../lib64/julia/sys.so
in process_options at /usr/bin/../lib64/julia/sys.so
in _start at /usr/bin/../lib64/julia/sys.so
while loading /home/grzes/julia_sucks/Main.jl, in expression starting on line 8
Obviously, it doesn't compile, because lentgh is misspelled. The problem is the message I received. expression starting on line 8 is simply main(). Julia hopelessly fails to point the invalid code fragment -- it just points to the invocation of main, but the erroneous line is not even in that file! Now imagine a real project where an error hides really deep in the call stack. Julia still wouldn't tell anything more than that the problem started on the entry point of the execution. It is impossible to work like that...
Is there a way to force Julia to give a little more precise messages?
In this case it's almost certainly a consequence of inlining: your printLength function is so short, it's almost certainly inlined into the call site, which is why you get the line number 8.
Eventually, it is expected that inlining won't cause problems for backtraces. At the moment, your best bet---if you're running julia's pre-release 0.4 version---is to start julia as julia --inline=no and run your tests again.
I am using the Kernel Density Estimator toolbox form http://www.ics.uci.edu/~ihler/code/kde.html . But I am getting the following error when I try to execute the demo files -
>> demo_kde_3
KDE Example #3 : Product sampling methods (single, anecdotal run)
Attempt to reference field of non-structure array.
Error in double (line 10)
if (npd.N > 0) d = 1; % return 1 if the density exists
Error in repmat (line 49)
nelems = prod(double(siz));
Error in kde (line 39)
if (size(ks,1) == 1) ks = repmat(ks,[size(points,1),1]); end;
Error in demo_kde_3 (line 8)
p = kde([.1,.45,.55,.8],.05); % create a mixture of 4 gaussians for
testing
Can anyone suggest what might be wrong? I am new to Matlab and having a hard time to figure out the problem.
Thank You,
Try changing your current directory away from the #kde folder; you may have to add the #kde folder to your path when you do this. For example run:
cd('c:\');
addpath('full\path\to\the\folder\#kde');
You may also need to add
addpath('full\path\to\the\folder\#kde\examples');
Then see if it works.
It looks like function repmat (a mathworks function) is picking up the #kde class's version of the double function, causing an error. Usually, only objects of the class #kde can invoke that functions which are in the #kde folder.
I rarely use the #folder form of class definitions, so I'm not completely sure of the semantics; I'm curious if this has any effect on the error.
In general, I would not recommend using the #folder class format for any development that you do. The mathworks overhauled their OO paradigm a few versions ago to a much more familiar (and useful) format. Use help classdef to see more. This #kde code seems to predate this upgrade.
MATLAB gives you the code line where the error occurs. As double and repmat belong to MATLAB, the bug probably is in kde.m line 39. Open that file in MATLAB debugger, set a breakpoint on that line (so the execution stops immediately before the execution of that specific line), and then when the code is stopped there, check the situation. Try the entire code line in console (copy-paste or type it, do not single-step, as causing an uncatched error while single-stepping ends the execution of code in debugger), it should give you an error (but doesn't stop execution). Then try pieces of the code of that code line, what works as it should and what not, eg. does the result of size(points, 1) make any sense.
However, debugging unfamiliar code is not an easy task, especially if you're a beginner in MATLAB. But if you learn and understand the essential datatypes of MATLAB (arrays, cell arrays and structs) and the different ways they can be addressed, and apply that knowledge to the situation on the line 39 of kde.m, hopefully you can fix the bug.
Repmat calls double and expects the built-in double to be called.
However I would guess that this is not part of that code:
if (npd.N > 0) d = 1; % return 1 if the density exists
So if all is correct this means that the buil-tin function double has been overloaded, and that this is the reason why the code crashes.
EDIT:
I see that #Pursuit has already addressed the issue but I will leave my answer in place as it describes the method of detection a bit more.
I am a bit of an R novice, and I am stuck with what seems like a simple problem, yet touches pretty deep questions about how and when things get evaluated in R.
I am using Rserve quite a bit; the typical syntax to get things evaluated remotely is a bit of a pain to type repeatedly:
RSeval(connection, quote(try(command)))
So I would like a function r which does the same thing with just the call:
r(command)
My first, naive, bound to fail attempt involved:
r <- function(command) {
RSeval(c, quote(try(command)))
}
You've guessed it: this sends, literally, try(command) to my confused Rserve daemon. I want command to be partially evaluated, if that makes any sense -- i.e. replaced by what I typed as an argument, but without evaluating it locally.
I looked for solutions to this, browsed throught the documentation for quote, substitute, eval, call, etc.. but I was not able to find something that worked. Either command gets evaluated locally, or not at all.
This is not a big problem, I can type the whole damn quote(try()) thing all the time; but at this point I am mostly curious as to how to get this to work!
EDIT:
More explanations as to what I want to do.
In the text above, command is meant to be a call do a function, ideally -- i.e., not a character string. Something like a <- 3 or assign("a", 3) rather than "a<-3" or quote(a<-3).
I believe that this is part of what makes this tricky. It seems really hard to tell R not to evaluate this locally, but only send it literally. Basically I would like my function to be a bit like quote(), which does not evaluate its argument.
Some explanation about my intentions. I wish to use Rserve frequently to pass commands to a remote R daemon. The commands would be my own (or my colleagues) and the daemon protected by firewall and authentication (and would not be run as root) -- so there is no worry of malicious commands being passed.
To be perfectly honest, this is not a big issue, and I would be pretty happy to always use the RSeval(c, quote(try())). At this point I see this more like an interesting inquiry into the subleties of R :-)
You probably want to use the substitute command, it can give you the argument unevaluated that you can build into the call.
I'm not sure if I understood you correctly - would eval(parse(text = command)) do the trick? Notice that command is a character, so you can easily pass it as a function argument. If I'm getting the point...
Anyway, evaluating user-specified commands is potentially malicious, therefore not recommended. You should either install AppArmor and tweak it (which is not an easy one), or drop the whole evaluation thing...