Julia #eval world age missmatch - matplotlib

Question

I'm trying to use the julia #eval functionality to only load the PyPlot package on demand. However I verry often run into world age missmatch.
Here is a minimal example where i try and plot on demand
function CreateMatrix(Ncount;Plot=true)
TheMatrix = fill(0.0,Ncount,Ncount)
if Plot
#eval using PyPlot
###"Plot the Matrix"
PyPlot.figure()
PyPlot.imshow(abs.(TheMatrix))
PyPlot.colorbar()
end
return TheMatrix
end
CreateMatrix(10;Plot=false)
CreateMatrix(10;Plot=true)
With the output
ERROR: LoadError: MethodError: no method matching figure()
The applicable method may be too new: running in world age 25063, while current world is 25079.
Closest candidates are:
figure(!Matched::Any...; kws...) at ~/.julia/packages/PyPlot/fZuOQ/src/PyPlot.jl:148 (method too new to be called from this world context.)
Stacktrace:
[1] #CreateMatrix#3(::Bool, ::Function, ::Int64) at myfile.jl:7
[2] (::getfield(Main, Symbol("#kw##CreateMatrix")))(::NamedTuple{(:Plot,),Tuple{Bool}}, ::typeof(CreateMatrix), ::Int64) at ./none:0
[3] top-level scope at none:0
[4] include at ./boot.jl:317 [inlined]
[5] include_relative(::Module, ::String) at ./loading.jl:1044
[6] include(::Module, ::String) at ./sysimg.jl:29
[7] exec_options(::Base.JLOptions) at ./client.jl:231
[8] _start() at ./client.jl:425
in expression starting at myfile.jl:16
Does anyone know how uses the #eval functionality properly?
EDIT
One of the comments suggested wrapping the plotting command and annotating with #noinline as below, but this does not work.
function CreateMatrix(Ncount;Plot=false)
TheMatrix = fill(0.0,Ncount,Ncount)
if Plot
#eval using PyPlot
###"Plot the Matrix"
ThePlotting(TheMatrix)
end
return TheMatrix
end
#noinline function ThePlotting(TheMatrix)
PyPlot.figure()
PyPlot.imshow(abs.(TheMatrix))
PyPlot.colorbar()
end
CreateMatrix(10;Plot=false)
CreateMatrix(10;Plot=true)
I'm running julia version 1.0.2

Answer 1

You can implement it like this:
function CreateMatrix(Ncount;Plot=true)
TheMatrix = fill(0.0,Ncount,Ncount)
if Plot
if isdefined(Main, :PyPlot)
println("PyPlot already loaded")
PyPlot.figure()
PyPlot.imshow(abs.(TheMatrix))
PyPlot.colorbar()
else
println("PyPlot loading PyPlot")
#eval using PyPlot
Base.invokelatest(PyPlot.figure)
Base.invokelatest(PyPlot.imshow, abs.(TheMatrix))
Base.invokelatest(PyPlot.colorbar)
end
end
return TheMatrix
end
I have used conditional to allow you to see which branch gets executed on repeated call to the function.
Initially I thought that when calling non-inlined function Julia allows world age change (but it turns out that it is strict).
Finally - in general it is probably safer not to write code like this but simply load the module in top-level scope (possibly conditionally).