prints from PythonCall or PyCall are buffered

[klaff]

If I make a notebook with two cells:
using PythonCall
and
pyprint("Hello world!")

or equivalently:
using PyCall
and
py"print('hello world!')"

the printed text does not appear in the terminal running the Pluto server until the notebook is closed or after a much larger amount of text (~ 10 kB?) has been printed. with_terminal() from PlutoUI doesn't work with this either.

[fonsp]

Thanks for the report! It looks like this is a bug in the combination of PyCall and Distributed:

julia> using Distributed

julia> p = Distributed.addprocs(1) |> first
2

julia> Distributed.remotecall_eval(Main, p, :(using PyCall))

julia> Distributed.remotecall_eval(Main, p, :(py"print('hello world!')"))

julia> # nothing is printed

julia> Distributed.rmprocs(p)
      From worker 2:	hello world!
Task (done) @0x000000011d5bf860

julia> 

Pluto uses the Distributed stdlib to manage notebook processes, which means that we probably won't be able to fix this on our side. Try reporting the example above to PyCall.jl or to julia.

[rashidrafeek]

As mentioned in the other issue: JuliaPy/PythonCall.jl#68 (comment), the following is a workaround:

pyprint("hello world", flush=true)