Forbid most operations for Context instances

powerline/lint/context.py

@@ -38,26 +38,36 @@ def list_themes(data, context):
 
 
 class Context(tuple):
-	def __new__(cls, base, other=None):
-		if other is not None:
-			return tuple.__new__(cls, tuple.__add__(base, other))
-		else:
-			return tuple.__new__(cls, ((MarkedUnicode('', base.mark), base),))
+	for func in dir(tuple):
+		if func in ('__getitem__', '__init__', '__getattribute__', '__len__', '__iter__'):
+			continue
+		exec((
+			'def {0}(self, *args, **kwargs):\n'
+			'	raise TypeError("{0} is not allowed for Context")'
+		).format(func))
+	del func
 
-	def __add__(self, arg):
-		assert(len(arg) == 1)
-		assert(type(arg) is tuple)
-		assert(len(arg[0]) == 2)
-		assert(type(arg[0]) is tuple)
-		havemarks(arg[0][0], arg[0][1])
-		return Context.__new__(Context, self, arg)
+	__slots__ = ()
+
+	def __new__(cls, base, context_key=None, context_value=None):
+		if context_key is not None:
+			assert(context_value is not None)
+			assert(type(base) is Context)
+			havemarks(context_key, context_value)
+			return tuple.__new__(cls, tuple.__add__(base, ((context_key, context_value),)))
+		else:
+			havemarks(base)
+			return tuple.__new__(cls, ((MarkedUnicode('', base.mark), base),))
 
 	@property
 	def key(self):
 		return key_sep.join((c[0] for c in self))
 
 	def enter_key(self, value, key):
-		return self + ((value.keydict[key], value[key]),)
+		return self.enter(value.keydict[key], value[key])
 
 	def enter_item(self, name, item):
-		return self + ((MarkedUnicode(name, item.mark), item),)
+		return self.enter(MarkedUnicode(name, item.mark), item)
+
+	def enter(self, context_key, context_value):
+		return Context.__new__(Context, self, context_key, context_value)