Make tag parameter to table constructor optional

If not provided, extract from class name.

2 files changed, 13 insertions, 1 deletions

diff --git a/Lib/fontTools/ttLib/__init__.py b/Lib/fontTools/ttLib/__init__.py
index 38664510..9b852a4d 100644
--- a/Lib/fontTools/ttLib/__init__.py
+++ b/Lib/fontTools/ttLib/__init__.py
@@ -816,6 +816,15 @@ def getTableClass(tag):
 	return tableClass
 
 
+def getClassTag(klass):
+	"""Fetch the table tag for a class object."""
+	name = klass.__name__
+	assert name[:6] == 'table_'
+	name = name[6:] # Chop 'table_'
+	return identifierToTag(name)
+
+
+
 def newTable(tag):
 	"""Return a new instance of a table."""
 	tableClass = getTableClass(tag)
diff --git a/Lib/fontTools/ttLib/tables/DefaultTable.py b/Lib/fontTools/ttLib/tables/DefaultTable.py
index e2e76851..3a6886c4 100644
--- a/Lib/fontTools/ttLib/tables/DefaultTable.py
+++ b/Lib/fontTools/ttLib/tables/DefaultTable.py
@@ -1,11 +1,14 @@
 from __future__ import print_function, division, absolute_import
 from fontTools.misc.py23 import *
+from fontTools.ttLib import getClassTag
 
 class DefaultTable(object):
 	
 	dependencies = []
 	
-	def __init__(self, tag):
+	def __init__(self, tag=None):
+		if tag is None:
+			tag = getClassTag(self.__class__)
 		self.tableTag = Tag(tag)
 	
 	def decompile(self, data, ttFont):