code: def main():
      
      inp,out="",""
      if '-h' in sys.argv:
          print(main.__doc__)
          sys.exit()
      if '-f' in sys.argv:
          ind=sys.argv.index('-f')
          file=sys.argv[ind+1]
          f=open(file,'r')
          inp=f.readlines()
      if '-F' in sys.argv:
          ind=sys.argv.index('-F')
          o=sys.argv[ind+1]
          out=open(o,'w')
      if '-i' in sys.argv:
          cont=1
          while cont==1:
              try:
                  b=1e-6*float(input('B (in microtesla): <cntl-D to quit '))
                  lat=float(input('Latitude: '))
              except:
                  print("\nGood bye\n")
                  sys.exit()
                   
              vdm= pmag.b_vdm(b,lat)
              print('%10.3e '%(vdm))
      if inp=="":
          inp = sys.stdin.readlines()  # read from standard input
      for line in inp:
          vdm=spitout(line)
          if out=="":
              print('%10.3e'%(vdm))
          else:
              out.write('%10.3e \n'%(vdm))
docs: NAME
          b_vdm.py
      
      DESCRIPTION
            converts B (in microT) and (magnetic) latitude to V(A)DM
   
      INPUT (COMMAND LINE ENTRY) 
             B (microtesla), latitude (positive north)
  
      OUTPUT
             V[A]DM
      
      SYNTAX
          b_vdm.py [command line options] [< filename]
      
      OPTIONS
          -h prints help and quits 
          -i for interactive data entry
          -f FILE input file
          -F FILE output