Parameter file in ArgParse.jl?

Question

Python's argparse has a simple way to read parameters from a file:

https://docs.python.org/2/library/argparse.html#fromfile-prefix-chars

Instead of passing your arguments one by one:

python script.py --arg1 val1 --arg2 val2 ...

You can say:

python script.py @args.txt

and then the arguments are read from args.txt.

Is there a way to do this in ArgParse.jl?

P.S.: If there is no "default" way of doing this, maybe I can do it by hand, by calling parse_args on a list of arguments read from a file. I know how to do this in a dirty way, but it gets messy if I want to replicate the behavior of argparse in Python, where I can pass multiple files with @, as well as arguments in the command line, and then the value of a parameter is simply the last value passed to this parameter. What's the best way of doing this?

Answer 1

This feature is not currently present in ArgParse.jl, although it would not be difficult to add. I have prepared a pull request.

In the interim, the following code suffices for what you need:

# faithful reproduction of Python 3.5.1 argparse.py
# partial copyright Python Software Foundation
function read_args_from_files(arg_strings, prefixes)
    new_arg_strings = AbstractString[]

    for arg_string in arg_strings
        if isempty(arg_string) || arg_string[1] ∉ prefixes
            # for regular arguments, just add them back into the list
            push!(new_arg_strings, arg_string)
        else
            # replace arguments referencing files with the file content
            open(arg_string[2:end]) do args_file
                arg_strings = AbstractString[]
                for arg_line in readlines(args_file)
                    push!(arg_strings, rstrip(arg_line, '\n'))
                end
                arg_strings = read_args_from_files(arg_strings, prefixes)
                append!(new_arg_strings, arg_strings)
            end
        end
    end

    # return the modified argument list
    return new_arg_strings
end

# preprocess args, then parse as usual
ARGS = read_args_from_files(ARGS, ['@'])
args = parse_args(ARGS, s)