# Apparent inconsistency importing modules

**URL:** <https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532>\
**Category:** General Usage\
**Created:** [April 25, 2018, 1:17pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532 "2018-04-25T13:17:34Z")\
**Posts on this page:** 13\
**Page:** 1

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**Author:** ![phrmoy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/phrmoy/32/8912_2.png) [@phrmoy](https://discourse.julialang.org/u/phrmoy)\
**Post date:** [April 25, 2018, 1:17pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/1 "2018-04-25T13:17:34Z")

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Hi there,  
I am new to Julia but I have written a few lines of Julia and I am still juggling with this, and it feels like I still don’t get it or I am not doing something right. So start off, when I want to import a module using `using` it seems I have two choices, I either `include` the file source file that has that module so I can then call `using`, or I append that directory to `LOAD_PATH`? I don’t really understand the latter. Like will Julia look inside source files in the loaded directories? And I am not sure I would want to modify global variables to have my software run?

I have something like

```julia
test.jl
Mod/Mod.jl

```

and tried `push!(LOAD_PATH, ".\\Mod")` from within `test.jl`, that did not work. I would like to understand how this works, but still, I would like for my software to just run without touching global variables.

But the main thing I am concerned about is this below

```julia
#mod1.jl
module Mod1
  x = 1
end

#mod2.jl
include("mod1.jl")
module Mod2
  using Mod1
  x = Mod1.x
end

#mod3.jl
module Mod3
  include("mod2.jl")
end

```

Here, `julia mod2.jl` works and `julia mod3.jl` doesn’t (it cannot load `Mod1`).

I have had a frustrating experience so far dealing with modules in Julia. Like, for instance, I tend to define `module_file_jl=nothing` inside `module_file.jl` so I can include as follows

`!isdefined(:module_file_jl) && include("module_file.jl")`

I have the above all over my code base as to avoid type reloads that lead to run-time errors where equivalent types do not match (this was painful for a while) when I include `module_file.jl` in several other files. But that trick solved the problem, but it certainly feels like a hack.

I have gone through the documentation for Modules, but I really need help here as this is bad (the way I am working on it). Thank you.

Pedro

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<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [April 25, 2018, 2:20pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/2 "2018-04-25T14:20:48Z")

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Ok, a few things:

1. Definitely don’t do the `!isdefined(:foo_jl) && include("foo.jl")` trick. That’s a C-ism that should never be needed in Julia.
2. When you do `import Foo` or `using Foo`, Julia looks in your package directory and then also looks in your `LOAD_PATH` for `Foo.jl` or `Foo/src/Foo.jl` (so yes, as you suspect, it does look inside your `src` folder).
3. `include()` is typically used when you want to split up a big module definition across multiple files. Using it to include a dependent module as you’ve done is a bit weird and probably not a good idea. Instead, if you rename your module files to match their module names (as in, `module Foo` in `Foo.jl` or `Foo/src/Foo.jl`) and ensure the folder containing your modules is in `LOAD_PATH`, then you can simply do:

```julia
# Mod1.jl
module Mod1
  x = 1
end

# Mod2.jl
module Mod2
  using Mod1
end

```

and so on.

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<div class="post-metadata">

**Author:** ![ScottPJones](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/scottpjones/32/146_2.png) [@ScottPJones](https://discourse.julialang.org/u/ScottPJones)\
**Post date:** [April 25, 2018, 2:23pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/3 "2018-04-25T14:23:21Z")

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1. edit: (thanks to rdeits) “I think you need a fully qualified path when you add it to `LOAD_PATH`, Julia doesn’t convert that relative path (or ones that start with `~` for your home directory) to an absolute path.” is wrong.

You do need to expand `~`, Julia does not handle it in paths.

1. You shouldn’t need to `include("mod1.jl")` in `mod2.jl`, if you have your LOAD\_PATH set up correctly, it will be able to find mod1.jl.

2. Same for Mod3, you shouldn’t need to include it, simply have `using Mod2`.

3. If you want these to be found when calling `julia` from the command line, make sure you have `JULIA_LOAD_PATH` set in your environment. See [JULIA\_LOAD\_PATH](https://docs.julialang.org/en/latest/manual/environment-variables/#JULIA_LOAD_PATH-1) in the documentation.

I hope this will be helpful!

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<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [April 25, 2018, 2:28pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/4 "2018-04-25T14:28:48Z")

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> I think you need a fully qualified path when you add it to LOAD\_PATH, Julia doesn’t convert that relative path (or ones that start with ~ for your home directory) to an absolute path.

That does not seem to be correct. For example, with `Foo.jl` in my current directory:

```julia
julia> push!(LOAD_PATH, ".")
3-element Array{Any,1}:
 "/home/rdeits/apps/julia-0.6.2/local/share/julia/site/v0.6"
 "/home/rdeits/apps/julia-0.6.2/share/julia/site/v0.6"      
 "."                                                        

julia> using Foo

```

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<div class="post-metadata">

**Author:** ![ScottPJones](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/scottpjones/32/146_2.png) [@ScottPJones](https://discourse.julialang.org/u/ScottPJones)\
**Post date:** [April 25, 2018, 2:30pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/5 "2018-04-25T14:30:21Z")

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OK. Good to know. I always run into the problem that Julia doesn’t handle the `~` for the home directory in paths.

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [April 25, 2018, 2:31pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/6 "2018-04-25T14:31:39Z")

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> [@ScottPJones](#):
>
> I always run into the problem that Julia doesn’t handle the `~` for the home directory in paths.

```julia
expanduser("~")

```

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<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [April 25, 2018, 2:32pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/7 "2018-04-25T14:32:10Z")

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Yeah, that’s a good point. `~` is only meaningful to your shell.

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**Author:** ![phrmoy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/phrmoy/32/8912_2.png) [@phrmoy](https://discourse.julialang.org/u/phrmoy)\
**Post date:** [April 25, 2018, 3:23pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/8 "2018-04-25T15:23:21Z")

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Thank you all for the input. I understand modules better now. Now, what if I have a deeper tree of source code,

dir0/  
dir0/dir1/  
dir0/dir1/dir2/

Do I need to add each one of these directories to LOAD\_PATH?

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**Author:** ![phrmoy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/phrmoy/32/8912_2.png) [@phrmoy](https://discourse.julialang.org/u/phrmoy)\
**Post date:** [April 25, 2018, 3:42pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/9 "2018-04-25T15:42:49Z")

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Also, I am able to use module `Foo` in `Foo.jl` but not in `Foo/src/Foo.jl`

So `push!(LOAD_PATH,"/Path/To/Foo")` works if I have `/Path/To/Foo/Foo.jl` but not `/Path/To/Foo/src/Foo.jl`

Am I missing something about the `Foo/src/Foo.jl`?

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<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [April 25, 2018, 3:45pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/10 "2018-04-25T15:45:28Z")

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In your case, you would need `/Path/To/Foo/Foo/src/Foo.jl` (you have to replace `Foo.jl` with `Foo/src/Foo.jl`). Or you could just add `/Path/To` to your `LOAD_PATH`.

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<div class="post-metadata">

**Author:** ![phrmoy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/phrmoy/32/8912_2.png) [@phrmoy](https://discourse.julialang.org/u/phrmoy)\
**Post date:** [April 25, 2018, 3:47pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/11 "2018-04-25T15:47:31Z")

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That worked! Thank you. Else regarding the comment above, we need to add each nested directory separately right?

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<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [April 25, 2018, 5:31pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/12 "2018-04-25T17:31:24Z")

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It’s true that `LOAD_PATH` is not recursive, so yes, you would need each folder containing a module on your path.

That said, I would suggest reconsidering your design. Having nested folders on your LOAD\_PATH is a pretty unusual design in Julia, and it will make it harder to, for example, publish any of those modules as a package for others to use. Much more typical is having a single folder containing all of your top-level modules, and then sub-folders only as necessary for organizing sub-modules.

For example, JuMP consists of a single module `JuMP` broken up into many files: [https://github.com/JuliaOpt/JuMP.jl/tree/master/src](https://github.com/JuliaOpt/JuMP.jl/tree/master/src) . It also has a sub-module called `Derivatives`, and that module’s definition is `include()`ed by the main `JuMP.jl`: [https://github.com/JuliaOpt/JuMP.jl/blob/c44401beb3ada8f2f36a9d12f8b4061f472d85b6/src/JuMP.jl#L24](https://github.com/JuliaOpt/JuMP.jl/blob/c44401beb3ada8f2f36a9d12f8b4061f472d85b6/src/JuMP.jl#L24) The result of all this is that you only need a single folder (wherever the entire JuMP repo lives) on your path, but you can still load JuMP with `using JuMP` and load its submodule with `using JuMP.Derivatives`.

Even better, if you’ve installed JuMP with `Pkg.add("JuMP")`, then it will be in your `Pkg.dir()` folder which is automatically available for `using` and `import` without any `LOAD_PATH` modification.

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<div class="post-metadata">

**Author:** ![phrmoy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/phrmoy/32/8912_2.png) [@phrmoy](https://discourse.julialang.org/u/phrmoy)\
**Post date:** [April 25, 2018, 8:41pm UTC](https://discourse.julialang.org/t/apparent-inconsistency-importing-modules/10532/13 "2018-04-25T20:41:34Z")

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Thanks for sharing that, and that makes more sense to me now.