# Julia throws additional LoadError during exception handling

**URL:** <https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446>\
**Category:** General Usage\
**Tags:** question, exception\
**Created:** [March 3, 2021, 9:49pm UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446 "2021-03-03T21:49:25Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![jonasjonker](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jonasjonker/32/22535_2.png) [@jonasjonker](https://discourse.julialang.org/u/jonasjonker)\
**Post date:** [March 3, 2021, 9:49pm UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/1 "2021-03-03T21:49:25Z")

</div>

I’m not really sure if this is the right place for this question, so please let me know where I should be if this is not the right place.

I’m new to Julia, and I am writing some scripts that I’d like to use from the Linux command line. This works all fine, but when I included some exception handling into my script I found that that whenever I throw an exception Julia throws an additional `LoadError` So for example if I run a script containing only the following line:

```nohighlight
throw(DivideError())

```

I get the both a DivideError (which I want) and a LoadError (Which I don’t want) when I run the script:

```bash
$ julia throwError.jl
ERROR: LoadError: DivideError: integer division error
Stacktrace:
 [1] top-level scope at /path/throwError.jl:1
 [2] include(::Function, ::Module, ::String) at ./Base.jl:380
 [3] include(::Module, ::String) at ./Base.jl:368
 [4] exec_options(::Base.JLOptions) at ./client.jl:296
 [5] _start() at ./client.jl:506
in expression starting at /path/throwError.jl:1

```

Can somebody explain what is happening here, and how I can prevent the LoadError?

---

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**Author:** ![adolgert](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/adolgert/32/20286_2.png) [@adolgert](https://discourse.julialang.org/u/adolgert)\
**Post date:** [March 3, 2021, 11:25pm UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/2 "2021-03-03T23:25:17Z")

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Hi Jonas! You provided a concise example, which makes it so much easier to help.

Julia runs the code in order to load it. If you put the `throw()` inside a function, then Julia will run the function definition, but it won’t run the function that gets defined. You won’t see the `DivideError` until later, when you call the function. So:

```julia
function suspicious_fry(x)
    throw(DivideError())
    x
end

```

---

<div class="post-metadata">

**Author:** ![jling](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jling/32/212909_2.png) [@jling](https://discourse.julialang.org/u/jling)\
**Post date:** [March 3, 2021, 11:35pm UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/3 "2021-03-03T23:35:56Z")

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in short, this is happening because you’re `throw`ing in global scope, which probably is not a realistic scenario.

---

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**Author:** ![jonasjonker](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jonasjonker/32/22535_2.png) [@jonasjonker](https://discourse.julialang.org/u/jonasjonker)\
**Post date:** [March 4, 2021, 12:29am UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/4 "2021-03-04T00:29:25Z")

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> [@adolgert](#):
>
> Julia runs the code in order to load it. If you put the `throw()` inside a function, then Julia will run the function definition, but it won’t run the function that gets defined. You won’t see the `DivideError` until later, when you call the function. So:

Hi aldogert,

Thank you for your answer. It is not so much that I have a problem, it’s more that I try to understand how Julia works. For me throwing exceptions works fine. I was just wondering why the `DivideError` is wrapped by a `LoadError`.

Putting the `throw()` inside a function changes the stacktrace slightly but doesn’t change the error that is thrown. I asked this question as well on [stackoverflow](https://stackoverflow.com/questions/66462136/why-does-julia-throw-an-loaderror-in-addition-to-the-error-i-want-to-throw) and somebody there pointed me to this [pull request](https://github.com/JuliaLang/julia/pull/31882#issuecomment-488224367) on github. What I understood from it is that Julia wraps exception throws in a `LoadError` as a way to show the stacktrace, but that they hope to deprecate this behavior at some point by improving backtracing in general.

But maybe somebody who has a better understanding of this, can phrase it more clearly than me.

---

<div class="post-metadata">

**Author:** ![adolgert](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/adolgert/32/20286_2.png) [@adolgert](https://discourse.julialang.org/u/adolgert)\
**Post date:** [March 4, 2021, 1:19am UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/5 "2021-03-04T01:19:51Z")

</div>

Hi Jonas. Maybe another way to understand this is to think about the Julia code for `include()`. It would look like this:

```julia
function include(filename)
    open(filename) do ofile
        for line in ofile
            try
                run(line)
            catch y
                throw(LoadError(y))
            end
        end
    end
end

```

So `run(line)` creates a DivideError, and then it gets caught and passed to the user as the reason loading wasn’t possible.

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<div class="post-metadata">

**Author:** ![jonasjonker](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jonasjonker/32/22535_2.png) [@jonasjonker](https://discourse.julialang.org/u/jonasjonker)\
**Post date:** [March 4, 2021, 9:24am UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/7 "2021-03-04T09:24:57Z")

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Hi Aldogert, Thanks for your code example. It made things more me clear for me.

However, I still think its peculiar that the `catch y throw(LoadError(y))` is/was necessary to show the line numbers in the stack trace (at least that is what I understood from the PR).

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<div class="post-metadata">

**Author:** ![pixel27](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pixel27/32/8902_2.png) [@pixel27](https://discourse.julialang.org/u/pixel27)\
**Post date:** [March 4, 2021, 3:42pm UTC](https://discourse.julialang.org/t/julia-throws-additional-loaderror-during-exception-handling/56446/8 "2021-03-04T15:42:49Z")

</div>

How about this, two files:

second.jl throws the exception only if the global `run` flag is set:

```julia
function panic_at_the_disco()
    throw(DivideError())
end

if run == true
    panic_at_the_disco()
end

```

The main file (first.jl):

```julia
run = false
include("second.jl")

try
    println(" *******************************")
    println("Calling panic...")
    panic_at_the_disco()
catch ex
    println("Exception caught: $(typeof(ex))")
    println()
end

try
    println(" *******************************")
    println("Running panic during include...")
    global run = true
    include("second.jl")
catch ex
    println("Exception caught: $(typeof(ex))")
    if ex isa LoadError
        println("Caused by: $(typeof(ex.error))")
    end
    println()
end

```

Output of running `first.jl`:

```julia
julia> include("first.jl")
*******************************
Calling panic...
Exception caught: DivideError

*******************************
Running panic during include...
Exception caught: LoadError
Caused by: DivideError

```

So `include()` wraps any exception thrown when loading/running the file in a `LoadError` but you can get the original error by accessing `ex.error`.