Fix unicode messages

gntp/core.py

@@ -35,6 +35,18 @@
 GNTP_EOL = gntp.shim.b('\r\n')
 GNTP_SEP = gntp.shim.b(': ')
 
+def is_string(var):
+	try:
+        	return isinstance(var, basestring)  # Python 2
+	except NameError:
+        	return isinstance(var, str)  # Python 3
+
+def convert_to_string(var):
+	try:
+		return unicode(var)  # Python 2
+	except NameError:
+		return str(var)  # Python 3
+
 
 class _GNTPBuffer(gntp.shim.StringIO):
 	"""GNTP Buffer class"""
@@ -44,8 +56,8 @@ def writeln(self, value=None):
 		self.write(GNTP_EOL)
 
 	def writeheader(self, key, value):
-		if not isinstance(value, str):
-			value = str(value)
+		if not is_string(value):
+			value = convert_to_string(value)
 		self.write(gntp.shim.b(key))
 		self.write(GNTP_SEP)
 		self.write(gntp.shim.b(value))