docs: def main():
      """
      NAME
         sundec.py
  
      DESCRIPTION
         calculates calculates declination from sun   compass measurements
  
      INPUT FORMAT
         GMT_offset, lat,long,year,month,day,hours,minutes,shadow_angle
         where GMT_offset is the hours to subtract from local time for GMT.
  
      SYNTAX
         sundec.py [-i][-f FILE] [< filename ]
  
      OPTIONS
          -i for interactive data entry
          -f FILE to set file name on command line 
           otherwise put data in input format in space delimited file
      OUTPUT:
          declination
   """
      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')
          data=f.readlines() # read in data from standard input
          for line in data: # step through line by line
              dec=spitout(line)
          sys.exit()
      if '-i' in sys.argv:
          while 1: # repeat this block until program killed
              sundata={}  # dictionary with sundata in it
              print ("Time difference between Greenwich Mean Time (hrs to subtract from local time to get GMT): ")
              try:
                  sundata["delta_u"]=input("<cntl-D> to quit ")
              except:
                  print("\n Good-bye\n")
                  sys.exit()
              date=""
              date=date+input("Year:  <cntl-D to quit> ")
              date=date+":"+input("Month:  ")
              date=date+":"+input("Day:  ")
              date=date+":"+input("hour:  ")
              date=date+":"+input("minute:  ")
              sundata["date"]=date
              sundata["lat"]=input("Latitude of sampling site (negative in southern hemisphere): ")
              sundata["lon"]=input("Longitude of sampling site (negative for western hemisphere): ")
              sundata["shadow_angle"]=input("Shadow angle: ")
              print('%7.1f'%(pmag.dosundec(sundata))) # call sundec function from pmag module and print
      else:
          data=sys.stdin.readlines() # read in data from standard input
      for line in data: # step through line by line
          dec=spitout(line)