Odd behavior regarding a list

[Edd Barrett]

Hi there,

My first post here, so hello :)

Just a little background, I am writing my dissertation, which is a JIT
compiler based upon LLVM and it's python bindings, along with the
aperiot LL(1) parser.

I have some code here, which is not behaving as I would expect. Could
someone enlighten me as to why this is so:

---8<---
	def __classdef_integer(self):
		"""
		class definition for a integer object.
		"""

		this_class = "Integer"

		# metadata inherited
		self.__class_data[this_class] = \
				self.__class_data["Object"]

		# cache parent struct sig for later (when casting ptrs)
		parent_struct_sig = \
				self.__class_data[this_class]["struct-sig"]

		this_cdata = self.__class_data[this_class]
		#this_cdata["membernames"].append("value")
		#this_cdata["type-sym"] = 1
		#this_cdata["parent-class"] = "Object"

		#vtab = self.__construct_vtable(this_class)
		#self.__ir_add_typesym(this_class, vtab)


		print "parent::::"
		print parent_struct_sig
		this_cdata["struct-sig"].append(self.__int_t)
		print "new::::"
		print parent_struct_sig

		sys.exit(1)
 ---8<---

Notice how I am caching the old value of 'parent_struct_sig' before I
manipulate it.

Produces the following output:

---8<---
parent::::
[<llvm.core.PointerType object at 0x7fcdfdac>]
new::::
[<llvm.core.PointerType object at 0x7fcdfdac>, <llvm.core.IntegerType
object at 0x8231520c>]
---8<---

My question is: why has 'parent_struct_sig' changed? I was under the
impression the assignment operator copies, not references.

Sorry if the answer is blindingly obvious. I am somewhat jaded from
working on this every day :P

Heres my python environment:
---8<---
Python 2.6.1 (r261:67515, Dec 27 2008, 16:56:14)
[GCC 4.2.0 20070307 (prerelease)] on openbsd4
Type "help", "copyright", "credits" or "license" for more information.
---8<---

Thanks