Custom message type cannot be properly displayed in REPL

[ShuhuaGao]

Following the beginner tutorial Creating a ROS msg and srv, we define a custom message type Num:

gsh@starfish:~/catkin_ws$ rosmsg show Num
[beginner_tutorials/Num]:
int64 num
uint8 age
string name

Then, the Python module for this message was generated with catkin_make. Next, we import the Num message into Julia as follows:

julia> using RobotOS

julia> @rosimport beginner_tutorials.msg.Num

julia> rostypegen()

julia> using .beginner_tutorials.msg: Num

julia> a = Num(-234, 12, "hello");

julia> a.name
"hello"

As observed above, RobotOS supports custom messages well. However, if we want to print the above variable a, we usually simply type a (or print(a)) in REPL. However, an error will be caused

julia> a  # or print(a)

Error information

Error showing value of type ERROR: MethodError: no method matching show_type_name(::IOContext{REPL.Terminals.TTYTerminal}, ::PyCall.PyObject)
Closest candidates are:
  show_type_name(::IO, ::Core.TypeName) at show.jl:555
Stacktrace:
 [1] show_datatype(::IOContext{REPL.Terminals.TTYTerminal}, ::DataType) at ./show.jl:618
 [2] show(::IOContext{REPL.Terminals.TTYTerminal}, ::Type) at ./show.jl:497
 [3] print(::IOContext{REPL.Terminals.TTYTerminal}, ::Type{T} where T) at ./strings/io.jl:35
 [4] print(::IOContext{REPL.Terminals.TTYTerminal}, ::String, ::Type{T} where T, ::Vararg{Any,N} where N) at ./strings/io.jl:46
 [5] println(::IOContext{REPL.Terminals.TTYTerminal}, ::String, ::Vararg{Any,N} where N) at ./strings/io.jl:73
 [6] print_response(::IO, ::Any, ::Bool, ::Bool, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:243
 [7] print_response(::REPL.AbstractREPL, ::Any, ::Bool, ::Bool) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:223
 [8] (::REPL.var"#do_respond#54"{Bool,Bool,REPL.var"#64#73"{REPL.LineEditREPL,REPL.REPLHistoryProvider},REPL.LineEditREPL,REPL.LineEdit.Prompt})(::Any, ::Any, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:822
 [9] #invokelatest#1 at ./essentials.jl:710 [inlined]
 [10] invokelatest at ./essentials.jl:709 [inlined]
 [11] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:2355
 [12] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:1143
 [13] (::REPL.var"#38#42"{REPL.LineEditREPL,REPL.REPLBackendRef})() at ./task.jl:356
caused by [exception 1]
MethodError: no method matching show_type_name(::IOContext{REPL.Terminals.TTYTerminal}, ::PyCall.PyObject)
Closest candidates are:
  show_type_name(::IO, ::Core.TypeName) at show.jl:555
Stacktrace:
 [1] show_datatype(::IOContext{REPL.Terminals.TTYTerminal}, ::DataType) at ./show.jl:618
 [2] show(::IOContext{REPL.Terminals.TTYTerminal}, ::Type) at ./show.jl:497
 [3] _show_default(::IOContext{REPL.Terminals.TTYTerminal}, ::Any) at ./show.jl:393
 [4] show_default at ./show.jl:389 [inlined]
 [5] show at ./show.jl:384 [inlined]
 [6] show(::IOContext{REPL.Terminals.TTYTerminal}, ::MIME{Symbol("text/plain")}, ::
SYSTEM (REPL): showing an error caused an error
ERROR: MethodError: no method matching show_type_name(::IOContext{REPL.Terminals.TTYTerminal}, ::PyCall.PyObject)
Closest candidates are:
  show_type_name(::IO, ::Core.TypeName) at show.jl:555
Stacktrace:
 [1] show_datatype(::IOContext{REPL.Terminals.TTYTerminal}, ::DataType) at ./show.jl:618
 [2] show(::IOContext{REPL.Terminals.TTYTerminal}, ::Type) at ./show.jl:497
 [3] print(::IOContext{REPL.Terminals.TTYTerminal}, ::Type{T} where T) at ./strings/io.jl:35
 [4] print(::IOContext{REPL.Terminals.TTYTerminal}, ::String, ::Type{T} where T, ::Vararg{Any,N} where N) at ./strings/io.jl:46
 [5] show_tuple_as_call(::IOContext{REPL.Terminals.TTYTerminal}, ::Symbol, ::Type{T} where T, ::Bool, ::Nothing) at ./show.jl:1788
 [6] show_tuple_as_call(::IOContext{REPL.Terminals.TTYTerminal}, ::Symbol, ::Type{T} where T, ::Bool) at ./show.jl:1755
 [7] show_spec_linfo(::IOContext{REPL.Terminals.TTYTerminal}, ::Base.StackTraces.StackFrame) at ./stacktraces.jl:242
 [8] show(::IOContext{REPL.Terminals.TTYTerminal}, ::Base.StackTraces.StackFrame; full_path::Bool) at ./stacktraces.jl:253
 [9] show_trace_entry(::IOContext{REPL.Terminals.TTYTerminal}, ::Base.StackTraces.StackFrame, ::Int64; prefix::String) at ./errorshow.jl:555
 [10] show_backtrace(::IOContext{REPL.Terminals.TTYTerminal}, ::Array{Base.StackTraces.StackFrame,1}) at ./errorshow.jl:659
 [11] showerror(::IOContext{REPL.Terminals.TTYTerminal}, ::MethodError, ::Array{Base.StackTraces.StackFrame,1}; backtrace::Bool) at ./errorshow.jl:93
 [12] show_exception_stack(::IOContext{REPL.Terminals.TTYTerminal}, ::Array{Any,1}) at ./errorshow.jl:737
 [13] display_error(::IOContext{REPL.Terminals.TTYTerminal}, ::Array{Any,1}) at ./client.jl:104
 [14] #invokelatest#1 at ./essentials.jl:710 [inlined]
 [15] invokelatest at ./essentials.jl:709 [inlined]
 [16] print_response(::IO, ::Any, ::Bool, ::Bool, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:233
 [17] print_response(::REPL.AbstractREPL, ::Any, ::Bool, ::Bool) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:223
 [18] (::REPL.var"#do_respond#54"{Bool,Bool,REPL.var"#64#73"{REPL.LineEditREPL,REPL.REPLHistoryProvider},REPL.LineEditREPL,REPL.LineEdit.Prompt})(::Any, ::Any, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:822
 [19] #invokelatest#1 at ./essentials.jl:710 [inlined]
 [20] invokelatest at ./essentials.jl:709 [inlined]
 [21] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:2355
 [22] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:1143
 [23] (::REPL.var"#38#42"{REPL.LineEditREPL,REPL.REPLBackendRef})() at ./task.jl:356

Additionally, we cannot help such a type either.

help?> Num
search: Number numerator Enum enumerate @enum isnumeric VersionNumber minimum

ERROR: KeyError: key "module" not found
Stacktrace:
 [1] getproperty(::PyCall.PyObject, ::String) at /home/gsh/.julia/packages/PyCall/zqDXB/src/PyCall.jl:301
 [2] getproperty(::PyCall.PyObject, ::Symbol) at /home/gsh/.julia/packages/PyCall/zqDXB/src/PyCall.jl:306
 [3] aliasof(::DataType, ::Any) at ./docs/bindings.jl:44
 [4] aliasof(::Base.Docs.Binding) at ./docs/bindings.jl:43
 [5] doc(::Base.Docs.Binding, ::Type{T} where T) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/docview.jl:174
 [6] doc(::Base.Docs.Binding) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/docview.jl:153
 [7] top-level scope at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/docview.jl:368

In the contrary, it is totally OK to print or help a built-in message like std_msgs.msg.String.

Version info

• ROS: noetic
• RobotOS v0.7.2
• Python 3.7.1
• Julia 1.5.0