Is there any R , python api available for flux.jl?

like dash, tensorflow, xgboost, lightgbm… have interface with R, python
why R, python interface not available for flux.jl?

You can use Flux through pyjulia.

You can use our JuliaConnectoR package from R. The README has examples on how to access Flux:
https://github.com/stefan-m-lenz/JuliaConnectoR

Is there an example, e.g. with custom loss function? For example I encountered this bug Error when trying to use Flux · Issue #491 · JuliaPy/pyjulia (github.com)