Chaining errors

New to Julia
,
1

When a dictionary cannot retrieve values it shows two error types, is it making a kind of chaining or is it just inside the error message?

LoadError: KeyError: key "d" not found
2

The LoadError is there because the error is happening during an include or using (see ?LoadError). It just prints the error that happened. Just accessing a Dict incorrectly by itself doesn’t show LoadError.

julia> d = Dict()
Dict{Any, Any}()

julia> d[1]
ERROR: KeyError: key 1 not found
Stacktrace:
 [1] getindex(h::Dict{Any, Any}, key::Int64)
   @ Base .\dict.jl:477
 [2] top-level scope
   @ REPL[7]:1
3 Likes
3

The KeyError can be found as a field error inside of the LoadError, so there is some chaining of errors here.

julia> f = tempname()
       open(f, "w") do io
           write(io, "d = Dict(); d['a']")
       end;

julia> global e  # or e = nothing: just make sure e exists outside of the try-catch scope
       try
           include(f)  # (or just  include_string(Main, "d = Dict(); d['a']") )
       catch e
       end

julia> dump(e)
LoadError
  file: String "(...)\\Temp\\jl_7aL81yn8zO"
  line: Int64 1
  error: KeyError
    key: key: Char 'a'

julia> e.error
KeyError('a')