ip_s:
   0.1 1.1.1.1
   0.5 1.2.3.4
ip_s_mask:
trash1:
   0.1 1.1.1.1
ip_d:
ip_d_mask:
   1.0 255.255.255.255

#!/usr/bin/python2.7
import re
types = [ 'ip_s', 'ip_d' ];
filename = "fields.conf"
def read_iter( f ):
  while True:
    line = f.readline( ) 
    if not line:
      break         
    line = line.strip( ).rstrip( ':' ) 
    if( not line ):
      continue
    yield line
f_iter = read_iter( open( filename ) ) 
one_word_re = re.compile( '^[0-9a-z_]+$' ) 
cdf = dict( ) 
try:
  line = f_iter.next( ) 
  while not line in types:
    line = f_iter.next( ) 
  cdf_key = line
  cdf[ cdf_key ] = []
       
  while True:
    line = f_iter.next( ) 
    while not one_word_re.search( line ):
      cdf[ cdf_key ].append( line ) 
      line = f_iter.next( ) 
         
    if( line.replace( '_mask', '' ) in types ):
      cdf_key = line
    else:
      cdf_key = 'trash'
    cdf[ cdf_key ] = []
except StopIteration:
  pass
del cdf[ 'trash' ] 
print( cdf ) 
 

def parse(fname, fields):
    result = {}
    field = None
    with open(fname, "rt", encoding="utf-8") as f:
        for line in f:
            line = line.strip()
            if not line:
                continue
            if line.endswith(":"):
                field = line[:-1] if line[:-1] in fields else None
                if field:
                    result[field] = []
            elif field:
                number, text = line.split(None, 1)
                result[field].append((float(number), text))
    return result
if "__main__" == __name__:
    print(parse("fields.conf", ("ip_s", "ip_d")))