Test #1 for using Python MDAnalysis module within the Julia numerical computing language

MDA_julia_test_1.jl

#if you don't have the Julia PyCall library you can install it with Pkg.add("PyCall") as the first line in this code
using PyCall
@pyimport MDAnalysis
#careful with dotted imports--need simpler module name representation for usage in Julia
@pyimport MDAnalysis.tests.datafiles as MDT 

#can now use MDAnalysis seamlessly and leverage some of the powerful features of the Julia numerical computing language
u = MDAnalysis.Universe(MDT.GRO,MDT.XTC) #although this works very naturally, many MDA methods currently require pycall invocation

all_atom_selection = pycall(u["selectAtoms"],PyAny,"all") #double quotes only for the "all" string--single quotes are character literals in Julia

#the natural call signature doesn't currently work in Julia so using the above workaround:
#all_atom_selection = u.selectAtoms("all") #careful! double quotes only because Julia uses single quotes for character literals, NOT strings

#Julia isn't finding method fields for a lot of MDAnalysis objects (can we fix this?); for now, pycall will do:
all_atom_coordinates = pycall(all_atom_selection["coordinates"],PyAny)
coord_type = typeof(all_atom_coordinates)
println("Julia type of all system coordinate array: $coord_type")

system_centroid = pycall(all_atom_selection["centroid"],PyAny)

println("Centroid of test system printed from Julia module: $system_centroid")