Julia is missing the deactivate command

[ptoche]

Thanks for the link. I’ll have to read that a few times.

Base.active_project() returns the path to a Project.toml even at startup, but that’s not quite the same as activating project… subtle.

Instead of trying to guess where Pkg.activate() will take me, I think I’d rather be explicit with something like:

cd("path/to/toml")
import Pkg
Pkg.activate(".")
Base.active_project()  # check you're where you think you are

Thanks again Fredrik

[magister-ludi]

I think you’re looking for what was written here, you just need to type
activate
(with no argument) in package mode.

[fredrikekre]

By default the load path is

julia> Base.LOAD_PATH
3-element Vector{String}:
 "@"
 "@v#.#"
 "@stdlib"

where @ is essentially a “pointer” to an active project. By default it doesn’t point to anything, it exands to nothing

julia> Base.load_path()
2-element Vector{String}:
 "/home/fredrik/.julia/environments/v1.6/Project.toml" # expansion of @v#.# in LOAD_PATH
 "/opt/julia/julia-1.6.1/share/julia/stdlib/v1.6"      # expansion of @stdlib in LOAD_PATH

If you Pkg.activate something you set the pointer to the thing you activated

julia> using Pkg; Pkg.activate("/tmp")

julia> Base.load_path()
3-element Vector{String}:
 "/tmp/Project.toml"
 "/home/fredrik/.julia/environments/v1.6/Project.toml"
 "/opt/julia/julia-1.6.1/share/julia/stdlib/v1.6"

and then Pkg.activate() (no argument) sets the pointer to “null” again:

julia> Pkg.activate()

julia> Base.load_path()
2-element Vector{String}:
 "/home/fredrik/.julia/environments/v1.6/Project.toml"
 "/opt/julia/julia-1.6.1/share/julia/stdlib/v1.6"

The --project command line flag, and the JULIA_PROJECT environment variable are other ways to set the pointer, similar to Pkg.activate.

[ptoche]

Thanks magister-ludi. Well I’m not so clear about the analogy with cd. It sounds as if once a project has been activated, the only way to deactivate it is to activate another project. I’m not sure I understand it.

[ptoche]

@fredrikekre

Pkg.activate() (no argument) sets the pointer to “null” again:

Thanks Fredrik, it’s much clearer now. I was confused when Base.active_project() was not returning a null pointer, but if you say it’s null I’ll take your word for it.

[magister-ludi]

I think the analogy is that in UNIX-like systems, cd without an argument takes you back to a a kind of ‘base state’, which is the home directory. So activate without an argument takes you back to the ‘no specific package loaded’ state.

Edit: I mean no specific package activated.

[ptoche]

@magister-ludi

takes you back to a a kind of ‘base state’,

yes, thanks. I was just not sure if that ‘base state’ was considered active or not.

[aiqc]

I came here looking for deactivate()

[ellocco]

status remark for v1.7.0:
I found confusing information regarding the environment variable “JULIA_LOAD_PATH”.
On the page about environment variables it is stated:

Unlike the shell PATH variable, empty entries in JULIA_LOAD_PATH are expanded to the default value of LOAD_PATH , ["@", "@v#.#", "@stdlib"] when populating LOAD_PATH . This allows easy appending, prepending, etc. of the load path value in shell scripts regardless of whether JULIA_LOAD_PATH is already set or not. For example, to prepend the directory /foo/bar to LOAD_PATH just do.

But under windows I have the impression that this is not true. Here is what I have added in my startup.jl:

s_modul_path = raw"C:\data\julia\MyLib"
ENV["JULIA_LOAD_PATH"] = s_modul_path

The startup file is executed at start up, I can see the welcome massage that is included.
My expectation was, that modules that are located in this folder will be found,
unfortunately this is not the case.

[carstenbauer]

• JULIA_LOAD_PATH != JULIA_DEPOT_PATH
• Once Julia is started, both environment variables have been processed and changing them won’t have any effect.
• To modifiy the load or depot path (stack) you need to modify the LOAD_PATH or DEPOT_PATH variables, respectively.

So I’d try something like push!(LOAD_PATH, s_modul_path).

[ellocco]

@carstenbauer

push!(LOAD_PATH, s_modul_path)

Yes, this works fine. In fact this is the method I use.
But I wonder, if the information about JULIA_LOAD_PATH is correct.
The following does not work:

ENV["JULIA_LOAD_PATH"] = string("C:\\data\\julia\\MyLib", ";", ENV["JULIA_LOAD_PATH"])

I hope this is the correct translation of the unix example:

export JULIA_LOAD_PATH="/foo/bar:$JULIA_LOAD_PATH"

The error message is:

LoadError: KeyError: key "JULIA_LOAD_PATH" not found

[fredrikekre]

It is not set by default, so you need something like

ENV["JULIA_LOAD_PATH"] = string("C:\\data\\julia\\MyLib", ";", get(ENV, "JULIA_LOAD_PATH", ""))

to mimic the shell behavior of just inserting an empty string for missing variables. (However, as noted above it is too late to change this once already in Julia.)

[StefanKarpinski]

You need to set the environment variable before starting Julia. Once you’re in Julia you can just manipulate the contents of LOAD_PATH directly.