docs: def main():
      """
      NAME
          vgp_di.py
      DESCRIPTION
        converts site latitude, longitude and pole latitude, longitude to declination, inclination
      
      SYNTAX
          vgp_di.py [-h] [-i] [-f FILE] [< filename]
      
      OPTIONS
          -h prints help message and quits
          -i interactive data entry
          -f FILE to specify file name on the command line
      
      INPUT 
        for file entry:
          PLAT PLON  SLAT SLON    
        where:
           PLAT: pole latitude 
           PLON: pole longitude (positive east)
           SLAT: site latitude (positive north)
           SLON: site longitude (positive east)
                 
      OUTPUT
          D I
          where:
             D: declination
             I: inclination
      """
      if '-h' in sys.argv:
          print(main.__doc__)
          sys.exit()
      if '-i' in sys.argv: # if one is -i
          while 1:
              try:
                  ans=input("Input Pole Latitude [positive north]: <cntrl-D to quit>  ")
                  plat=float(ans)  # assign input to plat, after conversion to floating point
                  ans=input("Input Pole Longitude [positive east]:  ")
                  plon =float(ans)
                  ans=input("Input Site Latitude:  ")
                  slat =float(ans)
                  ans=input("Input Site Longitude:  ")
                  slong =float(ans)
                  dec,inc=pmag.vgp_di(plat,plon,slat,slong)  # call vgp_di function from pmag module
                  print('%7.1f %7.1f'%(dec,inc)) # print out returned stuff
              except EOFError:
                  print("\n Good-bye\n")
                  sys.exit()
              
      elif '-f' in sys.argv: # manual input of file name
          ind=sys.argv.index('-f')
          file=sys.argv[ind+1]
          f=open(file,'r')
          inp = f.readlines()  # read from standard inp
          for line in inp:   # read in the data (as string variable), line by line
              dec,inc= spitout(line)
      else:
          inp = sys.stdin.readlines()  # read from standard input
          for line in inp:   # read in the data (as string variable), line by line
              spitout(line)