# Distributed+PyCall: cannot see exceptions ("cannot pickle 'traceback' object")

**URL:** <https://discourse.julialang.org/t/distributed-pycall-cannot-see-exceptions-cannot-pickle-traceback-object/59802>\
**Category:** New to Julia\
**Tags:** pycall, distributed\
**Created:** [April 22, 2021, 12:26pm UTC](https://discourse.julialang.org/t/distributed-pycall-cannot-see-exceptions-cannot-pickle-traceback-object/59802 "2021-04-22T12:26:41Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![dapz](https://avatars.discourse-cdn.com/v4/letter/d/a4c791/32.png) [@dapz](https://discourse.julialang.org/u/dapz)\
**Post date:** [April 22, 2021, 12:26pm UTC](https://discourse.julialang.org/t/distributed-pycall-cannot-see-exceptions-cannot-pickle-traceback-object/59802/1 "2021-04-22T12:26:41Z")

</div>

Hi, could someone tell me if the error which appears in the output below is a bug or if it should be expected for some reason? Even if it is not possible to convert the stacktrace for some reason, is there some workaround to at least see the error which has been thrown and the corresponding error message?

```julia
julia> using Distributed

julia> addprocs(1)
1-element Vector{Int64}:
 2

julia> @everywhere using PyCall

julia> fetch(@spawnat 2 py"""
       raise ZeroDivisionError
       """)
┌ Error: Fatal error on process 2
│ exception =
│ PyError ($(Expr(:escape, :(ccall(#= /home/me/.julia/packages/PyCall/BD546/src/pyfncall.jl:43 =# @pysym(:PyObject_Call), PyPtr, (PyPtr, PyPtr, PyPtr), o, pyargsptr, kw))))) <class 'TypeError'>
│ TypeError("cannot pickle 'traceback' object")
│    
│ Stacktrace:
│ [1] pyerr_check
│ @ ~/.julia/packages/PyCall/BD546/src/exception.jl:62 [inlined]
│ [2] pyerr_check
│ @ ~/.julia/packages/PyCall/BD546/src/exception.jl:66 [inlined]
│ [3] _handle_error(msg::String)
│ @ PyCall ~/.julia/packages/PyCall/BD546/src/exception.jl:83
│ [4] macro expansion
│ @ ~/.julia/packages/PyCall/BD546/src/exception.jl:97 [inlined]
│ [5] #107
│ @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:43 [inlined]
│ [6] disable_sigint
│ @ ./c.jl:458 [inlined]
│ [7] __pycall!
│ @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:42 [inlined]
│ [8] _pycall!(ret::PyObject, o::PyObject, args::Tuple{PyObject}, nargs::Int64, kw::Ptr{Nothing})
│ @ PyCall ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:29
│ [9] _pycall!
│ @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:11 [inlined]
│ [10] #pycall#112
│ @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:80 [inlined]
│ [11] pycall
│ @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:80 [inlined]
│ [12] serialize(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, pyo::PyObject)
│ @ PyCall ~/.julia/packages/PyCall/BD546/src/serialize.jl:14
│ [13] serialize_any(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, x::Any)
│ @ Serialization /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Serialization/src/Serialization.jl:649
│ [14] serialize(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, x::Any)
│ @ Serialization /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Serialization/src/Serialization.jl:628
│ [15] serialize(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, ex::CapturedException)
│ @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/clusterserialize.jl:205
│ [16] serialize_any(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, x::Any)
│ @ Serialization /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Serialization/src/Serialization.jl:649
│ [17] serialize(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, x::Any)
│ @ Serialization /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Serialization/src/Serialization.jl:628
│ [18] serialize_msg(s::Distributed.ClusterSerializer{Sockets.TCPSocket}, o::Distributed.ResultMsg)
│ @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/messages.jl:78
│ [19] #invokelatest#2
│ @ ./essentials.jl:708 [inlined]
│ [20] invokelatest
│ @ ./essentials.jl:706 [inlined]
│ [21] send_msg_(w::Distributed.Worker, header::Distributed.MsgHeader, msg::Distributed.ResultMsg, now::Bool)
│ @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/messages.jl:174
│ [22] send_msg_now
│ @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/messages.jl:118 [inlined]
│ [23] send_msg_now(s::Sockets.TCPSocket, header::Distributed.MsgHeader, msg::Distributed.ResultMsg)
│ @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/messages.jl:113
│ [24] deliver_result(sock::Sockets.TCPSocket, msg::Symbol, oid::Distributed.RRID, value::RemoteException)
│ @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/process_messages.jl:95
│ [25] macro expansion
│ @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/process_messages.jl:286 [inlined]
│ [26] (::Distributed.var"#105#107"{Distributed.CallMsg{:call_fetch}, Distributed.MsgHeader, Sockets.TCPSocket})()
│ @ Distributed ./task.jl:406
└ @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/process_messages.jl:99
Worker 2 terminated.ERROR: 
ProcessExitedException(2)
Stacktrace:
  [1] try_yieldto(undo::typeof(Base.ensure_rescheduled))
    @ Base ./task.jl:705
  [2] wait
    @ ./task.jl:764 [inlined]
  [3] wait(c::Base.GenericCondition{ReentrantLock})
    @ Base ./condition.jl:106
  [4] take_buffered(c::Channel{Any})
    @ Base ./channels.jl:389
  [5] take!(c::Channel{Any})
    @ Base ./channels.jl:383
  [6] take!(::Distributed.RemoteValue)
    @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:599
  [7] #remotecall_fetch#143
    @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:390 [inlined]
  [8] remotecall_fetch(f::Function, w::Distributed.Worker, args::Distributed.RRID)
    @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:386
  [9] #remotecall_fetch#146
    @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:421 [inlined]
 [10] remotecall_fetch
    @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:421 [inlined]
 [11] call_on_owner
    @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:494 [inlined]
 [12] fetch(r::Future)
    @ Distributed /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/remotecall.jl:533
 [13] top-level scope
    @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Distributed/src/macros.jl:99

```