Export of SymPy symbol from module gives ReadOnlyMemoryError

[mzaffalon]

When I import the following module

module MyMod
using SymPy: symbols
export b
b = symbols("b")
end

and I try to access b from the REPL, I get:

julia> using MyMod; b
Error showing value of type SymPy.Sym:
ERROR: ReadOnlyMemoryError()
Stacktrace:
 [1] macro expansion at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\exception.jl:93 [inlined]
 [2] #110 at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\pyfncall.jl:43 [inlined]
 [3] disable_sigint at .\c.jl:446 [inlined]
 [4] __pycall! at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\pyfncall.jl:42 [inlined]
 [5] _pycall!(::PyCall.PyObject, ::PyCall.PyObject, ::Tuple{SymPy.Sym}, ::Int64, ::Ptr{Nothing}) at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\pyfncall.jl:29
 [6] _pycall! at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\pyfncall.jl:11 [inlined]
 [7] #_#117 at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\pyfncall.jl:86 [inlined]
 [8] (::PyCall.PyObject)(::SymPy.Sym) at C:\Users\michele.zaffalon\.julia\packages\PyCall\zqDXB\src\pyfncall.jl:86
 [9] show(::IOContext{REPL.Terminals.TTYTerminal}, ::MIME{Symbol("text/plain")}, ::SymPy.Sym) at C:\Users\michele.zaffalon\.julia\packages\SymPy\7D3De\src\types.jl:73
 [10] display(::REPL.REPLDisplay, ::MIME{Symbol("text/plain")}, ::Any) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:137
 [11] display(::REPL.REPLDisplay, ::Any) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:141
 [12] display(::Any) at .\multimedia.jl:323
 [13] #invokelatest#1 at .\essentials.jl:712 [inlined]
 [14] invokelatest at .\essentials.jl:711 [inlined]
 [15] print_response(::IO, ::Any, ::Bool, ::Bool, ::Any) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:161
 [16] print_response(::REPL.AbstractREPL, ::Any, ::Bool, ::Bool) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:146
 [17] (::REPL.var"#do_respond#38"{Bool,REPL.var"#48#57"{REPL.LineEditREPL,REPL.REPLHistoryProvider},REPL.LineEditREPL,REPL.LineEdit.Prompt})(::Any, ::Any, ::Any) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:729
 [18] #invokelatest#1 at .\essentials.jl:712 [inlined]
 [19] invokelatest at .\essentials.jl:711 [inlined]
 [20] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\LineEdit.jl:2354
 [21] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:1055
 [22] run_repl(::REPL.AbstractREPL, ::Any) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.4\REPL\src\REPL.jl:206
 [23] (::Base.var"#764#766"{Bool,Bool,Bool,Bool})(::Module) at .\client.jl:383
 [24] #invokelatest#1 at .\essentials.jl:712 [inlined]
 [25] invokelatest at .\essentials.jl:711 [inlined]
 [26] run_main_repl(::Bool, ::Bool, ::Bool, ::Bool, ::Bool) at .\client.jl:367
 [27] exec_options(::Base.JLOptions) at .\client.jl:305
 [28] _start() at .\client.jl:484

Ref: https://discourse.julialang.org/t/export-of-sympy-symbol-from-module-gives-readonlymemoryerror/43426

[jverzani]

SOrry this took so long. It is cumbersome to do this, but https://github.com/jverzani/SymPyTest.jl/blob/master/src/SymPyTest.jl shows how.

One thing showing up in the test package is testing against x64 fails under travis.

[mzaffalon]

Thank you for taking the time of doing this.
After loading your example module, I still get a ERROR: UndefVarError: b not defined. Is this what you mean with the comment "no show method, so careful"?

[jverzani]

No, sorry. That comment is that showing this object b = SymPy.Sym(SymPy.PyCall.PyNULL()); before its __pyobject__ is set will cause an error. You should have a b defined when the package is loaded.

Can you run the tests in the package?

This worked for me on a new image from within a Jupyter notebook:

] add https://github.com/jverzani/SymPyTest.jl

] test SymPyTest

If that fails, I wonder if there is an underlying OS issue.

[mzaffalon]

Sorry for the delayed answer. Yes, the test run. I ended up doing something like this:

module SymPyExportDefs

using SymPy

export a, b, c

const a = SymPy.Sym(SymPy.PyCall.PyNULL());
const b = SymPy.Sym(SymPy.PyCall.PyNULL());
const c = SymPy.Sym(SymPy.PyCall.PyNULL());

function __init__()
    copy!(a.__pyobject__, SymPy.PyCall.PyObject(SymPy.symbols("a", positive=true)))
    copy!(b.__pyobject__, SymPy.PyCall.PyObject(SymPy.symbols("b")))
    copy!(c.__pyobject__, SymPy.PyCall.PyObject(a + b))
end

end

and the output is

julia> c
a + b
julia> c - a
b
julia> sqrt(a^2)
a

Indeed exporting a definition is cumbersome.

[jverzani]

Yeah, that is how it needs to be done. It isn't pretty, but seemingly needed to work with run-time generated objects from python.