1 files changed, 104 insertions, 0 deletions
diff --git a/intern/python/modules/mcf/utils/singletonlist.py b/intern/python/modules/mcf/utils/singletonlist.py
new file mode 100644
index 00000000000..5ca2f5000c2
--- /dev/null
+++ b/intern/python/modules/mcf/utils/singletonlist.py
@@ -0,0 +1,104 @@
+class SingletonList:
+	'''
+	A SingletonList always has a length of one or 0,
+	appends overwrite the single element, iteration will
+	return precisely one element.  Attempts to get any item
+	other than 0 will raise an IndexError or return the single
+	item depending on whether the 'raiseIndexError' flag is
+	true or false (generally it should be true except if the
+	for x in SingletonList: construct is known never to be
+	used, since this construct will create an infinite loop
+	if we never raise an IndexError).
+	'''
+	def __init__(self,base=None,raiseIndexError=1):
+		self._base = base
+		self.raiseIndexError = raiseIndexError
+	def __len__(self):
+		'''
+		The length is 0 if no _base, 1 if a base
+		'''
+		if hasattr(self, '_base'):
+			return 1
+		else:
+			return 0
+	def __getitem__(self,ind):
+		'''
+		Get the item if ind == 0, else raise an IndexError or return
+		the item, depending on the raiseIndexError flag
+		'''
+		if ind == 0:
+			try:
+				return self._base
+			except AttributeError:
+				raise IndexError, ind
+		elif self.raiseIndexError:
+			raise IndexError, ind
+		else:
+			return self._base
+	def __setitem__(self,ind, item):
+		'''
+		The item is to become the base
+		'''
+		self._base = item
+	def __delitem__(self,ind):
+		'''
+		Delete the base, regardless of the index used
+		'''
+		try:
+			del(self._base)
+		except AttributeError:
+			raise IndexError, ind
+	def append(self,item):
+		'''
+		Replace the base with the item
+		'''
+		self._base = item
+	def index(self,item):
+		'''
+		if the item is the base, return the only valid index (0)
+		'''
+		try:
+			if item == self._base:
+				return 0
+		except:
+			pass
+		raise ValueError, item
+	def count(self, item):
+		'''
+		If the item is the base, we have one, else 0
+		'''
+		try:
+			if item == self._base:
+				return 1
+		except:
+			pass
+		return 0
+	insert = __setitem__
+	def remove(self, item):
+		'''
+		if the item is the base, delete the base, else ValueError
+		'''
+		try:
+			if item == self._base:
+				del(self._base)
+				return
+		except:
+			pass
+		raise ValueError, item
+	def reverse(self):
+		pass
+	def sort(self):
+		pass
+	def __repr__(self):
+		try:
+			return '[%s]'%`self._base`
+		except AttributeError:
+			return '[]'
+	# store and copy functions
+#	def __getinitargs__(self):
+#		return (self._base,self.raiseIndexError)
+#	def __getstate__(self,*args,**namedargs):
+#		pass
+#	def __setstate__(self,*args,**namedargs):
+#		pass
+