StackOverFlow Question prep.txt

I'm using Python 3 to parse a file that contains a list of key value pairs. One pair per line.
The keys are known as markers, and begin with a backslash. 
This file describes the keys used in other files in something like the way a dtd describes an xml file.

I've omitted most key value pairs for clarity.
The key value pairs are grouped together, each group starts with a key: \+mkr and ends with a key \-mkr
The value of the first key is the marker that is being described.

The data describes the hierarchy of the markers that's the information I'm trying to parse.

\+mkr lx
\nam  Entry
\mkrOverThis
\-mkr

\+mkr ps
\nam Part of speech
\mkrOverThis lx
\-mkr

\+mkr ex
\nam Example
\mkrOverThis ps
\-mkr

This is code I have:
def read_typ_file(filein):
	typ, filetype = process_input_file(filein, '.typ')
	defined_markers = []
	Marker = namedtuple('Marker',['mkr','nam','mkrOverThis'])

	# Little error checking here, but file computer generated so usually consistent.
	for entry in typ:
		mkr = name = parent = None
		for field in entry:
			key , value = field
			print('key is : {}, and value is {}'.format(key,value))
			if key == '\\+mkr':
				mkr = value
			if key == '\\nam':
				name = value
			if key == '\\mkrOverThis':
				parent = value
			if key == '\\-mkr':
				this_marker = Marker(mkr,name,parent)
				defined_markers.append(this_marker)
			
	groups = dict()
	print("HERE")
	for marker in defined_markers:
		print(marker)
		print(marker[2])
		#continue
	for marker in defined_markers:
		print("There are {} defined markers.\nGroups are: {}".format(len(defined_markers),groups))
		if marker.mkrOverThis not in groups.keys():
			groups[marker.mkrOverThis] = [marker.mkr]
		elif marker.mkrOverThis:
			groups[marker.mkrOverThis].append(marker.mkr)
		else :
			raise ValueError("There seems to be a problem with marker {} in read_typ_file.".format(marker))

	print("\nGroups found are as follows:")
	for group in groups:
		print("Marker for parent group: {}".format(group))
		print("{}".format(groups[group]))
		
		

	# Little error checking here, but file computer generated so usually consistent.
	for entry in typ:
		for field in entry:
			key , value = field
			print('key is : {}, and value is {}'.format(key,value))
			marker_dict = {'marker' : None,'name' : None,'language' : None,'parent_marker' : None,'character_style' : None}
			if key == '\\+mkr':
				marker_dict.update([['marker', value]])
			if key == '\\nam':
				marker_dict['name'] = value
			if key == '\\lng':
				marker_dict['language'] = value
			if key == '\\mkrOverThis':
				marker_dict.update([['parent_marker', value]])
			if key == '\\CharStyle':
				marker_dict.update([['character_style',  value]])
			print('marker_dict is {}'.format(marker_dict))
			if key == '\\-mkr':
				defined_markers.append(marker_dict)