<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def main():
 """ NAME extract_methods.py DESCRIPTION reads in a magic table and creates a file with method codes SYNTAX extract_methods.py [command line options] OPTIONS -h: prints the help message and quits. -f FILE: specify magic format input file, default is magic_measurements.txt -F FILE: specify method code output file, default is magic_methods.txt """

    citation='This study'
    args=sys.argv
    outfile='magic_methods.txt'
    infile='magic_measurements.txt'
#
# get command line arguments
#
    dir_path='.'
    if '-WD' in args:
        ind=args.index("-WD")
        dir_path=args[ind+1]
    if "-h" in args:
        print(main.__doc__)
        sys.exit()
    if '-F' in args:
        ind=args.index("-F")
        outfile=args[ind+1]
    if '-f' in args:
        ind=args.index("-f")
        infile=args[ind+1]
    infile=dir_path+'/'+infile
    outfile=dir_path+'/'+outfile
    data,file_type=pmag.magic_read(infile)
    MethRecs=[]
    methods=[]
    for rec in data:
        meths=rec['magic_method_codes'].split(":")
        for meth in meths:
            if meth not in methods:
                MethRec={}
                methods.append(meth)
                MethRec['magic_method_code']=meth
                MethRecs.append(MethRec)
    pmag.magic_write(outfile,MethRecs,'magic_methods')