docs: def main():
      """
      NAME
          dia_vgp.py
      DESCRIPTION
        converts declination inclination alpha95 to virtual geomagnetic pole, dp and dm
      
      SYNTAX
          dia_vgp.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:
          D I A95 SLAT SLON      
        where:
           D: declination
           I: inclination
           A95: alpha_95
           SLAT: site latitude (positive north)
           SLON: site longitude (positive east)
                 
      OUTPUT
          PLON PLAT DP DM
          where:
               PLAT: pole latitude 
               PLON: pole longitude (positive east)
               DP: 95% confidence angle in parallel 
               DM: 95% confidence angle in meridian 
      """
      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 Declination: <cntrl-D to quit>  ")
                  Dec=float(ans)  # assign input to Dec, after conversion to floating point
                  ans=input("Input Inclination:  ")
                  Inc =float(ans)
                  ans=input("Input Alpha 95:  ")
                  a95 =float(ans)
                  ans=input("Input Site Latitude:  ")
                  slat =float(ans)
                  ans=input("Input Site Longitude:  ")
                  slong =float(ans)
                  spitout(Dec,Inc,a95,slat,slong)  # call dia_vgp function from pmag module
                  print('%7.1f %7.1f %7.1f %7.1f'%(plong,plat,dp,dm)) # print out returned stuff
              except:
                  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')
          inlist  = []
          for line in f.readlines():
              inlist.append([])
              # loop over the elements, split by whitespace
              for el in line.split():
                  inlist[-1].append(float(el))
          spitout(inlist)
  
      else:
          input = sys.stdin.readlines()  # read from standard input
          inlist  = []
          for line in input:   # read in the data (as string variable), line by line
              inlist.append([])
              # loop over the elements, split by whitespace
              for el in line.split():
                  inlist[-1].append(float(el))
          spitout(inlist)