Reflection to discover function keyword arguments in Julia

I needed to extract the named keyword arguments for a function in Julia. In Python we have the inspect.getargspec function but in Julia there doesn’t seem to be any standard way to do so. Obviously it’s possible because calling methods on a function lists them at the REPL.

julia> versioninfo()
Julia Version 0.5.0
Commit 3c9d753 (2016-09-19 18:14 UTC)
Platform Info:
  System: Linux (x86_64-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU E3-1505M v5 @ 2.80GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.7.1 (ORCJIT, broadwell)

julia> using Clustering

julia> methods(kmeans)
# 1 method for generic function "kmeans":
kmeans(X::Array{T<:Any,2}, k::Int64; weights, init, maxiter, tol, display) at /home/cryan/.julia/v0.5/Clustering/src/kmeans.jl:49
...

Digging through methodsshow.jl in Base we can pull the three lines that do what we want.

julia> ml = methods(kmeans)
# 1 method for generic function "kmeans":
kmeans(X::Array{T<:Any,2}, k::Int64; weights, init, maxiter, tol, display) at /home/cryan/.julia/v0.5/Clustering/src/kmeans.jl:49

julia> m = collect(ml)[1]
kmeans(X::Array{T<:Any,2}, k::Int64) at /home/cryan/.julia/v0.5/Clustering/src/kmeans.jl:49

julia> kwargs = Base.kwarg_decl(m.sig, typeof(ml.mt.kwsorter))
5-element Array{Any,1}:
 :weights
 :init   
 :maxiter
 :tol    
 :display

Since this is not exported from Base there is no guarantee it will work in future versions of Julia.

#software #julia