diff --git a/src/diana/sgfParser.py b/src/diana/sgfParser.py
--- a/src/diana/sgfParser.py
+++ b/src/diana/sgfParser.py
@@ -6,8 +6,6 @@ def skipWhitespace(str,start):
 	return i
 
 class Collection:
-	gameTrees=[]
-	
 	def __init__(self,str):
 		self.gameTrees=[]
 		i,x=GameTree.create(str,0)
@@ -19,8 +17,9 @@ class Collection:
 			i,x=GameTree.create(str,i)
 	
 class GameTree:
-	nodes=[]
-	branches=[]
+	def __init__(self):
+		self.nodes=[]
+		self.branches=[]
 	
 	# def __init__(self,str,start):
 		# self.nodes=[]
@@ -39,7 +38,8 @@ class GameTree:
 			# print("error when parsing GameTree")
 			# return (-1,None)
 		# return (i+1,self)
-		
+
+	@staticmethod
 	def create(str,start):
 		res=GameTree()
 		i=skipWhitespace(str,start)
@@ -66,8 +66,10 @@ class GameTree:
 		return (i+1,res)
 	
 class Node:
-	properties=dict()
-	
+	def __init__(self):
+		self.properties=dict()
+
+	@staticmethod
 	def create(str,start):
 		res=Node()
 		if str[start]!=";":
@@ -77,7 +79,8 @@ class Node:
 		i,x=Property.create(str,start+1)
 		while x is not None:
 			if x.name in res.properties:
-				print('error: duplicate "{0}" property in node at position {1}. second value ignored'.format(x.name,start))
+				print(res.properties)
+				raise ParserError(0,0,'duplicate "{0}" property in node at position {1}. second value ignored'.format(x.name,start))
 			else:
 				res.properties[x.name]=x
 			i=skipWhitespace(str,i)
@@ -93,9 +96,11 @@ class Node:
 		else: return None
 	
 class Property:
-	name=""
-	value=""
-	
+	def __init__(self):
+		self.name=""
+		self.value=""
+
+	@staticmethod
 	def create(str,start):
 		res=Property()
 		i,x=Property.ident(str,start)
@@ -111,7 +116,8 @@ class Property:
 			# i=skipWhitespace(str,i)
 			# i,x=PropValue.create(str,i,res.name)
 		return (i,res)
-		
+
+	@staticmethod
 	def ident(str,start):
 		r=re.compile(r"[A-Z]+")
 		m=r.match(str,start)
@@ -119,10 +125,13 @@ class Property:
 		return (m.end(),m.group())
 
 class PropValue:
-	type=""
-	value=None
+	def __init__(self):
+		self.type=""
+		self.value=None
+
 	patterns=dict()
-	
+
+	@staticmethod
 	def create(str,start,name):
 		if name in PropValue.patterns:
 			return PropValue.patterns[name](str,start)
@@ -138,7 +147,7 @@ class PropValue:
 		# if str[i]!="]":
 			# return (start,None)
 		# return (i+1,x)
-	
+
 	def choose(*vTypes):
 		def f(str,start):
 			for vType in vTypes:
@@ -146,7 +155,7 @@ class PropValue:
 				if x is not None: return (i,x)
 			return (start,None)
 		return f
-	
+
 	def singleton(vType):
 		def f(str,start):
 			if str[start]!="[":
@@ -167,11 +176,11 @@ class PropValue:
 			# i,x=singleton(str,i,vType)
 		# if len(res)==0 and not allowEmpty: return (start,None)
 		# return (i,res)
-		
+
 	def listOf(vType,allowEmpty=False):
 		def f(str,start):
 			res=[]
-			single=singleton(vType)
+			single=PropValue.singleton(vType)
 			i,x=single(str,start)
 			while x!=None:
 				res.append(x)
@@ -186,7 +195,7 @@ class PropValue:
 		# i,b=vTypeB(str,i+1)
 		# if b==None: return start,None
 		# return (i,(a,b))
-		
+
 	def compose(vTypeA,vTypeB):
 		def f(str,start):
 			i,a=vTypeA(str,start)
@@ -197,28 +206,28 @@ class PropValue:
 			if b==None: return start,None
 			return (i,(a,b))
 		return f
-	
+
 	def number(str,start):
 		r=re.compile(r"(\+|-|)\d+")
 		m=r.match(str,start)
 		if m is None: return (start,None)
 		res=int(m.group(0))
 		return (m.end(),res)
-		
+
 	def real(str,start):
 		r=re.compile(r"(\+|-|)\d+(\.\d+)?")
 		m=r.match(str,start)
 		if m is None: return (start,None)
 		res=float(m.group(0))
 		return (m.end(),res)
-		
+
 	def double(str,start):
 		r=re.compile(r"1|2")
 		m=r.match(str,start)
 		if m is None: return (start,None)
 		res=int(m.group(0))
 		return (m.end(),res)
-	
+
 	def color(str,start):
 		r=re.compile(r"B|W")
 		m=r.match(str,start)
@@ -240,7 +249,7 @@ class PropValue:
 			# else:
 				# res+=c
 		# return res
-	
+
 	def text(simple=True,composed=False):
 		def f(str,start):
 			res=""
@@ -264,9 +273,9 @@ class PropValue:
 				lastC=c
 			return (i,res)
 		return f
-		
+
 	def empty(str,start): return (start,"")
-	
+
 	def anything(str,start):
 		esc=False
 		for i,c in enumerate(str[start:],start):
@@ -363,6 +372,14 @@ class PropValue:
 		"TW":listOf(point,allowEmpty=True)
 	}
 
+class ParserError(Exception):
+	def __init__(self,line,col,message):
+		self.line=line
+		self.col=col
+		self.message=message
+
+
+
 """def property(str):
 	# i=propIdent(str)
 	# if i<0: return -1