How do I reload a module in an active Julia session after an edit?

Question

2018 Update: Be sure to check all the responses, as the answer to this question has changed multiple times over the years. At the time of this update, the <

Answer 1

In julia v0.6.0 it seems like using workspace() is no longer necessary: I can simply reload(MyModule) in an active REPL session, and it works as expected (chages made to the source file that contains MyModule are reflected in the active REPL session).

This applies to modules that have been brought into scope by either import or using

Answer 2

I wanted to create a new module from scratch, and tried the different answers with 1.0 and didn’t get a satisfactory result, but I found the following worked for me:

From the Julia REPL in the directory I want to use for my project I run

pkg> generate MyModule

This creates a subdirectory like the following structure:

MyModule
├── Project.toml
└── src
    └── MyModule.jl

I put my module code in MyModule.jl. I change to the directory MyModule (or open it in my IDE) and add a file Scratch.jl with the following code:

Pkg.activate(“.”)
using Revise
import MyModule

Then I can add my code to test below and everything updates without reloading the REPL.

Answer 3

In my humble opinion, the better way is to use import from the very beginning instead of using for the reported issue.

Consider the module:

module ModuleX1
  export produce_text
  produce_text() = begin
    println("v1.0") 
  end
  println("v1.0 loaded")
end

Then in REPL:

julia> import ModuleX1
v1.0 loaded

julia> ModuleX1.produce_text()
v1.0

Update the code of the module and save it:

module ModuleX1
  export produce_text
  produce_text() = begin
    println("v2.0")  
  end
  println("v2.0 loaded")
end

Next, in the REPL:

julia> reload("ModuleX1")
Warning: replacing module ModuleX1
v2.0 loaded

julia> ModuleX1.produce_text()
v2.0

Advantages of using import over using:

• avoiding ambiguity in function calls (What to call: ModuleX1.produce_text() or produce_text() after reloading?)
• do not have to call workspace() in order to get rid of ambiguity

Disadvantages of using import over using:

• a fully qualified name in every call for every exported name is needed

Edited: Discarded "full access to the module, even to the not-exported names" from "Disadvantages..." according to the conversation below.

Answer 4

The basis of this problem is the confluence of reloading a module, but not being able to redefine a thing in the module Main (see the documentation here) -- that is at least until the new function workspace() was made available on July 13 2014. Recent versions of the 0.3 pre-release should have it.

Before workspace()

Consider the following simplistic module

module TstMod
export f

function f()
   return 1
end

end

Then use it....

julia> using TstMod

julia> f()
1

If the function f() is changed to return 2 and the module is reloaded, f is in fact updated. But not redefined in module Main.

julia> reload("TstMod")
Warning: replacing module TstMod

julia> TstMod.f()
2

julia> f()
1

The following warnings make the problem clear

julia> using TstMod
Warning: using TstMod.f in module Main conflicts with an existing identifier.

julia> using TstMod.f
Warning: ignoring conflicting import of TstMod.f into Main

Using workspace()

However, the new function workspace() clears Main preparing it for reloading TstMod

julia> workspace()

julia> reload("TstMod")

julia> using TstMod

julia> f()
2

Also, the previous Main is stored as LastMain

julia> whos()
Base                          Module
Core                          Module
LastMain                      Module
Main                          Module
TstMod                        Module
ans                           Nothing

julia> LastMain.f()
1

Answer 5

Use the package Revise, e.g.

Pkg.add("Revise") # do this only once

include("src/my_module.jl")
using Revise
import my_module

You may need to start this in a new REPL session. Notice the use of import instead of using, because using does not redefine the function in the Main module (as explained by @Maciek Leks and @waTeim).

Other solutions: Two advantages of Revise.jl compared to workspace() are that (1) it is much faster, and (2) it is future-proof, as workspace() was deprecated in 0.7, as discussed in this GitHub issue:

julia> VERSION
v"0.7.0-DEV.3089"

julia> workspace()
ERROR: UndefVarError: workspace not defined

and a GitHub contributor recommended Revise.jl:

Should we add some mesage like "workspace is deprecated, check out Revise.jl instead"?

Even in Julia 0.6.3, the three previous solutions of workspace(), import, and reload fail when a module called other modules, such as DataFrames. With all three methods, I got the same error when I called that module the second time in the same REPL:

ERROR: LoadError: MethodError: all(::DataFrames.##58#59, ::Array{Any,1}) is ambiguous. Candidates: ...

I also got many warning messages such as:

WARNING: Method definition macroexpand(Module, ANY) in module Compat at /Users/mmorin/.julia/v0.6/Compat/src/Compat.jl:87 overwritten in module Compat at /Users/mmorin/.julia/v0.6/Compat/src/Compat.jl:87.

Restarting the Julia session worked, but it was cumbersome. I found this issue in the Reexport package, with a similar error message:

MethodError: all(::Reexport.##2#6, ::Array{Any,1}) is ambiguous.

and followed the suggestion of one contributor:

Does this happen without using workspace()? That function is notorious for interacting poorly with packages, which is partly why it was deprecated in 0.7.