diff --git a/_pytest/assertion/__init__.py b/_pytest/assertion/__init__.py
index 26fed96b4..9f89d17fc 100644
--- a/_pytest/assertion/__init__.py
+++ b/_pytest/assertion/__init__.py
@@ -31,15 +31,16 @@ def pytest_configure(config):
     config._cleanup.append(m.undo)
     warn_about_missing_assertion()
     if not config.getvalue("noassert") and not config.getvalue("nomagic"):
+        from _pytest.assertion import reinterpret
         def callbinrepr(op, left, right):
             hook_result = config.hook.pytest_assertrepr_compare(
                 config=config, op=op, left=left, right=right)
             for new_expl in hook_result:
                 if new_expl:
                     return '\n~'.join(new_expl)
-        m.setattr(py.builtin.builtins,
-                  'AssertionError', py.code._AssertionError)
-        m.setattr(py.code, '_reprcompare', callbinrepr)
+        m.setattr(py.builtin.builtins, 'AssertionError',
+                  reinterpret.AssertionError)
+        m.setattr(sys.modules[__name__], '_reprcompare', callbinrepr)
     else:
         rewrite_asserts = None
 
@@ -98,6 +99,53 @@ def warn_about_missing_assertion():
         sys.stderr.write("WARNING: failing tests may report as passing because "
         "assertions are turned off!  (are you using python -O?)\n")
 
+# if set, will be called by assert reinterp for comparison ops
+_reprcompare = None
+
+def _format_explanation(explanation):
+    """This formats an explanation
+
+    Normally all embedded newlines are escaped, however there are
+    three exceptions: \n{, \n} and \n~.  The first two are intended
+    cover nested explanations, see function and attribute explanations
+    for examples (.visit_Call(), visit_Attribute()).  The last one is
+    for when one explanation needs to span multiple lines, e.g. when
+    displaying diffs.
+    """
+    raw_lines = (explanation or '').split('\n')
+    # escape newlines not followed by {, } and ~
+    lines = [raw_lines[0]]
+    for l in raw_lines[1:]:
+        if l.startswith('{') or l.startswith('}') or l.startswith('~'):
+            lines.append(l)
+        else:
+            lines[-1] += '\\n' + l
+
+    result = lines[:1]
+    stack = [0]
+    stackcnt = [0]
+    for line in lines[1:]:
+        if line.startswith('{'):
+            if stackcnt[-1]:
+                s = 'and   '
+            else:
+                s = 'where '
+            stack.append(len(result))
+            stackcnt[-1] += 1
+            stackcnt.append(0)
+            result.append(' +' + '  '*(len(stack)-1) + s + line[1:])
+        elif line.startswith('}'):
+            assert line.startswith('}')
+            stack.pop()
+            stackcnt.pop()
+            result[stack[-1]] += line[1:]
+        else:
+            assert line.startswith('~')
+            result.append('  '*len(stack) + line[1:])
+    assert len(stack) == 1
+    return '\n'.join(result)
+
+
 # Provide basestring in python3
 try:
     basestring = basestring
diff --git a/_pytest/assertion/newinterpret.py b/_pytest/assertion/newinterpret.py
new file mode 100644
index 000000000..1d061aa46
--- /dev/null
+++ b/_pytest/assertion/newinterpret.py
@@ -0,0 +1,340 @@
+"""
+Find intermediate evalutation results in assert statements through builtin AST.
+This should replace oldinterpret.py eventually.
+"""
+
+import sys
+import ast
+
+import py
+from _pytest import assertion
+from _pytest.assertion import _format_explanation
+from _pytest.assertion.reinterpret import BuiltinAssertionError
+
+
+if sys.platform.startswith("java") and sys.version_info < (2, 5, 2):
+    # See http://bugs.jython.org/issue1497
+    _exprs = ("BoolOp", "BinOp", "UnaryOp", "Lambda", "IfExp", "Dict",
+              "ListComp", "GeneratorExp", "Yield", "Compare", "Call",
+              "Repr", "Num", "Str", "Attribute", "Subscript", "Name",
+              "List", "Tuple")
+    _stmts = ("FunctionDef", "ClassDef", "Return", "Delete", "Assign",
+              "AugAssign", "Print", "For", "While", "If", "With", "Raise",
+              "TryExcept", "TryFinally", "Assert", "Import", "ImportFrom",
+              "Exec", "Global", "Expr", "Pass", "Break", "Continue")
+    _expr_nodes = set(getattr(ast, name) for name in _exprs)
+    _stmt_nodes = set(getattr(ast, name) for name in _stmts)
+    def _is_ast_expr(node):
+        return node.__class__ in _expr_nodes
+    def _is_ast_stmt(node):
+        return node.__class__ in _stmt_nodes
+else:
+    def _is_ast_expr(node):
+        return isinstance(node, ast.expr)
+    def _is_ast_stmt(node):
+        return isinstance(node, ast.stmt)
+
+
+class Failure(Exception):
+    """Error found while interpreting AST."""
+
+    def __init__(self, explanation=""):
+        self.cause = sys.exc_info()
+        self.explanation = explanation
+
+
+def interpret(source, frame, should_fail=False):
+    mod = ast.parse(source)
+    visitor = DebugInterpreter(frame)
+    try:
+        visitor.visit(mod)
+    except Failure:
+        failure = sys.exc_info()[1]
+        return getfailure(failure)
+    if should_fail:
+        return ("(assertion failed, but when it was re-run for "
+                "printing intermediate values, it did not fail.  Suggestions: "
+                "compute assert expression before the assert or use --no-assert)")
+
+def run(offending_line, frame=None):
+    if frame is None:
+        frame = py.code.Frame(sys._getframe(1))
+    return interpret(offending_line, frame)
+
+def getfailure(failure):
+    explanation = _format_explanation(failure.explanation)
+    value = failure.cause[1]
+    if str(value):
+        lines = explanation.splitlines()
+        if not lines:
+            lines.append("")
+        lines[0] += " << %s" % (value,)
+        explanation = "\n".join(lines)
+    text = "%s: %s" % (failure.cause[0].__name__, explanation)
+    if text.startswith("AssertionError: assert "):
+        text = text[16:]
+    return text
+
+
+operator_map = {
+    ast.BitOr : "|",
+    ast.BitXor : "^",
+    ast.BitAnd : "&",
+    ast.LShift : "<<",
+    ast.RShift : ">>",
+    ast.Add : "+",
+    ast.Sub : "-",
+    ast.Mult : "*",
+    ast.Div : "/",
+    ast.FloorDiv : "//",
+    ast.Mod : "%",
+    ast.Eq : "==",
+    ast.NotEq : "!=",
+    ast.Lt : "<",
+    ast.LtE : "<=",
+    ast.Gt : ">",
+    ast.GtE : ">=",
+    ast.Pow : "**",
+    ast.Is : "is",
+    ast.IsNot : "is not",
+    ast.In : "in",
+    ast.NotIn : "not in"
+}
+
+unary_map = {
+    ast.Not : "not %s",
+    ast.Invert : "~%s",
+    ast.USub : "-%s",
+    ast.UAdd : "+%s"
+}
+
+
+class DebugInterpreter(ast.NodeVisitor):
+    """Interpret AST nodes to gleam useful debugging information. """
+
+    def __init__(self, frame):
+        self.frame = frame
+
+    def generic_visit(self, node):
+        # Fallback when we don't have a special implementation.
+        if _is_ast_expr(node):
+            mod = ast.Expression(node)
+            co = self._compile(mod)
+            try:
+                result = self.frame.eval(co)
+            except Exception:
+                raise Failure()
+            explanation = self.frame.repr(result)
+            return explanation, result
+        elif _is_ast_stmt(node):
+            mod = ast.Module([node])
+            co = self._compile(mod, "exec")
+            try:
+                self.frame.exec_(co)
+            except Exception:
+                raise Failure()
+            return None, None
+        else:
+            raise AssertionError("can't handle %s" %(node,))
+
+    def _compile(self, source, mode="eval"):
+        return compile(source, "<assertion interpretation>", mode)
+
+    def visit_Expr(self, expr):
+        return self.visit(expr.value)
+
+    def visit_Module(self, mod):
+        for stmt in mod.body:
+            self.visit(stmt)
+
+    def visit_Name(self, name):
+        explanation, result = self.generic_visit(name)
+        # See if the name is local.
+        source = "%r in locals() is not globals()" % (name.id,)
+        co = self._compile(source)
+        try:
+            local = self.frame.eval(co)
+        except Exception:
+            # have to assume it isn't
+            local = False
+        if not local:
+            return name.id, result
+        return explanation, result
+
+    def visit_Compare(self, comp):
+        left = comp.left
+        left_explanation, left_result = self.visit(left)
+        for op, next_op in zip(comp.ops, comp.comparators):
+            next_explanation, next_result = self.visit(next_op)
+            op_symbol = operator_map[op.__class__]
+            explanation = "%s %s %s" % (left_explanation, op_symbol,
+                                        next_explanation)
+            source = "__exprinfo_left %s __exprinfo_right" % (op_symbol,)
+            co = self._compile(source)
+            try:
+                result = self.frame.eval(co, __exprinfo_left=left_result,
+                                         __exprinfo_right=next_result)
+            except Exception:
+                raise Failure(explanation)
+            try:
+                if not result:
+                    break
+            except KeyboardInterrupt:
+                raise
+            except:
+                break
+            left_explanation, left_result = next_explanation, next_result
+
+        if assertion._reprcompare is not None:
+            res = assertion._reprcompare(op_symbol, left_result, next_result)
+            if res:
+                explanation = res
+        return explanation, result
+
+    def visit_BoolOp(self, boolop):
+        is_or = isinstance(boolop.op, ast.Or)
+        explanations = []
+        for operand in boolop.values:
+            explanation, result = self.visit(operand)
+            explanations.append(explanation)
+            if result == is_or:
+                break
+        name = is_or and " or " or " and "
+        explanation = "(" + name.join(explanations) + ")"
+        return explanation, result
+
+    def visit_UnaryOp(self, unary):
+        pattern = unary_map[unary.op.__class__]
+        operand_explanation, operand_result = self.visit(unary.operand)
+        explanation = pattern % (operand_explanation,)
+        co = self._compile(pattern % ("__exprinfo_expr",))
+        try:
+            result = self.frame.eval(co, __exprinfo_expr=operand_result)
+        except Exception:
+            raise Failure(explanation)
+        return explanation, result
+
+    def visit_BinOp(self, binop):
+        left_explanation, left_result = self.visit(binop.left)
+        right_explanation, right_result = self.visit(binop.right)
+        symbol = operator_map[binop.op.__class__]
+        explanation = "(%s %s %s)" % (left_explanation, symbol,
+                                      right_explanation)
+        source = "__exprinfo_left %s __exprinfo_right" % (symbol,)
+        co = self._compile(source)
+        try:
+            result = self.frame.eval(co, __exprinfo_left=left_result,
+                                     __exprinfo_right=right_result)
+        except Exception:
+            raise Failure(explanation)
+        return explanation, result
+
+    def visit_Call(self, call):
+        func_explanation, func = self.visit(call.func)
+        arg_explanations = []
+        ns = {"__exprinfo_func" : func}
+        arguments = []
+        for arg in call.args:
+            arg_explanation, arg_result = self.visit(arg)
+            arg_name = "__exprinfo_%s" % (len(ns),)
+            ns[arg_name] = arg_result
+            arguments.append(arg_name)
+            arg_explanations.append(arg_explanation)
+        for keyword in call.keywords:
+            arg_explanation, arg_result = self.visit(keyword.value)
+            arg_name = "__exprinfo_%s" % (len(ns),)
+            ns[arg_name] = arg_result
+            keyword_source = "%s=%%s" % (keyword.arg)
+            arguments.append(keyword_source % (arg_name,))
+            arg_explanations.append(keyword_source % (arg_explanation,))
+        if call.starargs:
+            arg_explanation, arg_result = self.visit(call.starargs)
+            arg_name = "__exprinfo_star"
+            ns[arg_name] = arg_result
+            arguments.append("*%s" % (arg_name,))
+            arg_explanations.append("*%s" % (arg_explanation,))
+        if call.kwargs:
+            arg_explanation, arg_result = self.visit(call.kwargs)
+            arg_name = "__exprinfo_kwds"
+            ns[arg_name] = arg_result
+            arguments.append("**%s" % (arg_name,))
+            arg_explanations.append("**%s" % (arg_explanation,))
+        args_explained = ", ".join(arg_explanations)
+        explanation = "%s(%s)" % (func_explanation, args_explained)
+        args = ", ".join(arguments)
+        source = "__exprinfo_func(%s)" % (args,)
+        co = self._compile(source)
+        try:
+            result = self.frame.eval(co, **ns)
+        except Exception:
+            raise Failure(explanation)
+        pattern = "%s\n{%s = %s\n}"
+        rep = self.frame.repr(result)
+        explanation = pattern % (rep, rep, explanation)
+        return explanation, result
+
+    def _is_builtin_name(self, name):
+        pattern = "%r not in globals() and %r not in locals()"
+        source = pattern % (name.id, name.id)
+        co = self._compile(source)
+        try:
+            return self.frame.eval(co)
+        except Exception:
+            return False
+
+    def visit_Attribute(self, attr):
+        if not isinstance(attr.ctx, ast.Load):
+            return self.generic_visit(attr)
+        source_explanation, source_result = self.visit(attr.value)
+        explanation = "%s.%s" % (source_explanation, attr.attr)
+        source = "__exprinfo_expr.%s" % (attr.attr,)
+        co = self._compile(source)
+        try:
+            result = self.frame.eval(co, __exprinfo_expr=source_result)
+        except Exception:
+            raise Failure(explanation)
+        explanation = "%s\n{%s = %s.%s\n}" % (self.frame.repr(result),
+                                              self.frame.repr(result),
+                                              source_explanation, attr.attr)
+        # Check if the attr is from an instance.
+        source = "%r in getattr(__exprinfo_expr, '__dict__', {})"
+        source = source % (attr.attr,)
+        co = self._compile(source)
+        try:
+            from_instance = self.frame.eval(co, __exprinfo_expr=source_result)
+        except Exception:
+            from_instance = True
+        if from_instance:
+            rep = self.frame.repr(result)
+            pattern = "%s\n{%s = %s\n}"
+            explanation = pattern % (rep, rep, explanation)
+        return explanation, result
+
+    def visit_Assert(self, assrt):
+        test_explanation, test_result = self.visit(assrt.test)
+        if test_explanation.startswith("False\n{False =") and \
+                test_explanation.endswith("\n"):
+            test_explanation = test_explanation[15:-2]
+        explanation = "assert %s" % (test_explanation,)
+        if not test_result:
+            try:
+                raise BuiltinAssertionError
+            except Exception:
+                raise Failure(explanation)
+        return explanation, test_result
+
+    def visit_Assign(self, assign):
+        value_explanation, value_result = self.visit(assign.value)
+        explanation = "... = %s" % (value_explanation,)
+        name = ast.Name("__exprinfo_expr", ast.Load(),
+                        lineno=assign.value.lineno,
+                        col_offset=assign.value.col_offset)
+        new_assign = ast.Assign(assign.targets, name, lineno=assign.lineno,
+                                col_offset=assign.col_offset)
+        mod = ast.Module([new_assign])
+        co = self._compile(mod, "exec")
+        try:
+            self.frame.exec_(co, __exprinfo_expr=value_result)
+        except Exception:
+            raise Failure(explanation)
+        return explanation, value_result
diff --git a/_pytest/assertion/oldinterpret.py b/_pytest/assertion/oldinterpret.py
new file mode 100644
index 000000000..3e8f1c0b3
--- /dev/null
+++ b/_pytest/assertion/oldinterpret.py
@@ -0,0 +1,556 @@
+import py
+import sys, inspect
+from compiler import parse, ast, pycodegen
+from _pytest.assertion import _format_explanation
+from _pytest.assertion.reinterpret import BuiltinAssertionError
+
+passthroughex = py.builtin._sysex
+
+class Failure:
+    def __init__(self, node):
+        self.exc, self.value, self.tb = sys.exc_info()
+        self.node = node
+
+class View(object):
+    """View base class.
+
+    If C is a subclass of View, then C(x) creates a proxy object around
+    the object x.  The actual class of the proxy is not C in general,
+    but a *subclass* of C determined by the rules below.  To avoid confusion
+    we call view class the class of the proxy (a subclass of C, so of View)
+    and object class the class of x.
+
+    Attributes and methods not found in the proxy are automatically read on x.
+    Other operations like setting attributes are performed on the proxy, as
+    determined by its view class.  The object x is available from the proxy
+    as its __obj__ attribute.
+
+    The view class selection is determined by the __view__ tuples and the
+    optional __viewkey__ method.  By default, the selected view class is the
+    most specific subclass of C whose __view__ mentions the class of x.
+    If no such subclass is found, the search proceeds with the parent
+    object classes.  For example, C(True) will first look for a subclass
+    of C with __view__ = (..., bool, ...) and only if it doesn't find any
+    look for one with __view__ = (..., int, ...), and then ..., object,...
+    If everything fails the class C itself is considered to be the default.
+
+    Alternatively, the view class selection can be driven by another aspect
+    of the object x, instead of the class of x, by overriding __viewkey__.
+    See last example at the end of this module.
+    """
+
+    _viewcache = {}
+    __view__ = ()
+
+    def __new__(rootclass, obj, *args, **kwds):
+        self = object.__new__(rootclass)
+        self.__obj__ = obj
+        self.__rootclass__ = rootclass
+        key = self.__viewkey__()
+        try:
+            self.__class__ = self._viewcache[key]
+        except KeyError:
+            self.__class__ = self._selectsubclass(key)
+        return self
+
+    def __getattr__(self, attr):
+        # attributes not found in the normal hierarchy rooted on View
+        # are looked up in the object's real class
+        return getattr(self.__obj__, attr)
+
+    def __viewkey__(self):
+        return self.__obj__.__class__
+
+    def __matchkey__(self, key, subclasses):
+        if inspect.isclass(key):
+            keys = inspect.getmro(key)
+        else:
+            keys = [key]
+        for key in keys:
+            result = [C for C in subclasses if key in C.__view__]
+            if result:
+                return result
+        return []
+
+    def _selectsubclass(self, key):
+        subclasses = list(enumsubclasses(self.__rootclass__))
+        for C in subclasses:
+            if not isinstance(C.__view__, tuple):
+                C.__view__ = (C.__view__,)
+        choices = self.__matchkey__(key, subclasses)
+        if not choices:
+            return self.__rootclass__
+        elif len(choices) == 1:
+            return choices[0]
+        else:
+            # combine the multiple choices
+            return type('?', tuple(choices), {})
+
+    def __repr__(self):
+        return '%s(%r)' % (self.__rootclass__.__name__, self.__obj__)
+
+
+def enumsubclasses(cls):
+    for subcls in cls.__subclasses__():
+        for subsubclass in enumsubclasses(subcls):
+            yield subsubclass
+    yield cls
+
+
+class Interpretable(View):
+    """A parse tree node with a few extra methods."""
+    explanation = None
+
+    def is_builtin(self, frame):
+        return False
+
+    def eval(self, frame):
+        # fall-back for unknown expression nodes
+        try:
+            expr = ast.Expression(self.__obj__)
+            expr.filename = '<eval>'
+            self.__obj__.filename = '<eval>'
+            co = pycodegen.ExpressionCodeGenerator(expr).getCode()
+            result = frame.eval(co)
+        except passthroughex:
+            raise
+        except:
+            raise Failure(self)
+        self.result = result
+        self.explanation = self.explanation or frame.repr(self.result)
+
+    def run(self, frame):
+        # fall-back for unknown statement nodes
+        try:
+            expr = ast.Module(None, ast.Stmt([self.__obj__]))
+            expr.filename = '<run>'
+            co = pycodegen.ModuleCodeGenerator(expr).getCode()
+            frame.exec_(co)
+        except passthroughex:
+            raise
+        except:
+            raise Failure(self)
+
+    def nice_explanation(self):
+        return _format_explanation(self.explanation)
+
+
+class Name(Interpretable):
+    __view__ = ast.Name
+
+    def is_local(self, frame):
+        source = '%r in locals() is not globals()' % self.name
+        try:
+            return frame.is_true(frame.eval(source))
+        except passthroughex:
+            raise
+        except:
+            return False
+
+    def is_global(self, frame):
+        source = '%r in globals()' % self.name
+        try:
+            return frame.is_true(frame.eval(source))
+        except passthroughex:
+            raise
+        except:
+            return False
+
+    def is_builtin(self, frame):
+        source = '%r not in locals() and %r not in globals()' % (
+            self.name, self.name)
+        try:
+            return frame.is_true(frame.eval(source))
+        except passthroughex:
+            raise
+        except:
+            return False
+
+    def eval(self, frame):
+        super(Name, self).eval(frame)
+        if not self.is_local(frame):
+            self.explanation = self.name
+
+class Compare(Interpretable):
+    __view__ = ast.Compare
+
+    def eval(self, frame):
+        expr = Interpretable(self.expr)
+        expr.eval(frame)
+        for operation, expr2 in self.ops:
+            if hasattr(self, 'result'):
+                # shortcutting in chained expressions
+                if not frame.is_true(self.result):
+                    break
+            expr2 = Interpretable(expr2)
+            expr2.eval(frame)
+            self.explanation = "%s %s %s" % (
+                expr.explanation, operation, expr2.explanation)
+            source = "__exprinfo_left %s __exprinfo_right" % operation
+            try:
+                self.result = frame.eval(source,
+                                         __exprinfo_left=expr.result,
+                                         __exprinfo_right=expr2.result)
+            except passthroughex:
+                raise
+            except:
+                raise Failure(self)
+            expr = expr2
+
+class And(Interpretable):
+    __view__ = ast.And
+
+    def eval(self, frame):
+        explanations = []
+        for expr in self.nodes:
+            expr = Interpretable(expr)
+            expr.eval(frame)
+            explanations.append(expr.explanation)
+            self.result = expr.result
+            if not frame.is_true(expr.result):
+                break
+        self.explanation = '(' + ' and '.join(explanations) + ')'
+
+class Or(Interpretable):
+    __view__ = ast.Or
+
+    def eval(self, frame):
+        explanations = []
+        for expr in self.nodes:
+            expr = Interpretable(expr)
+            expr.eval(frame)
+            explanations.append(expr.explanation)
+            self.result = expr.result
+            if frame.is_true(expr.result):
+                break
+        self.explanation = '(' + ' or '.join(explanations) + ')'
+
+
+# == Unary operations ==
+keepalive = []
+for astclass, astpattern in {
+    ast.Not    : 'not __exprinfo_expr',
+    ast.Invert : '(~__exprinfo_expr)',
+    }.items():
+
+    class UnaryArith(Interpretable):
+        __view__ = astclass
+
+        def eval(self, frame, astpattern=astpattern):
+            expr = Interpretable(self.expr)
+            expr.eval(frame)
+            self.explanation = astpattern.replace('__exprinfo_expr',
+                                                  expr.explanation)
+            try:
+                self.result = frame.eval(astpattern,
+                                         __exprinfo_expr=expr.result)
+            except passthroughex:
+                raise
+            except:
+                raise Failure(self)
+
+    keepalive.append(UnaryArith)
+
+# == Binary operations ==
+for astclass, astpattern in {
+    ast.Add    : '(__exprinfo_left + __exprinfo_right)',
+    ast.Sub    : '(__exprinfo_left - __exprinfo_right)',
+    ast.Mul    : '(__exprinfo_left * __exprinfo_right)',
+    ast.Div    : '(__exprinfo_left / __exprinfo_right)',
+    ast.Mod    : '(__exprinfo_left % __exprinfo_right)',
+    ast.Power  : '(__exprinfo_left ** __exprinfo_right)',
+    }.items():
+
+    class BinaryArith(Interpretable):
+        __view__ = astclass
+
+        def eval(self, frame, astpattern=astpattern):
+            left = Interpretable(self.left)
+            left.eval(frame)
+            right = Interpretable(self.right)
+            right.eval(frame)
+            self.explanation = (astpattern
+                                .replace('__exprinfo_left',  left .explanation)
+                                .replace('__exprinfo_right', right.explanation))
+            try:
+                self.result = frame.eval(astpattern,
+                                         __exprinfo_left=left.result,
+                                         __exprinfo_right=right.result)
+            except passthroughex:
+                raise
+            except:
+                raise Failure(self)
+
+    keepalive.append(BinaryArith)
+
+
+class CallFunc(Interpretable):
+    __view__ = ast.CallFunc
+
+    def is_bool(self, frame):
+        source = 'isinstance(__exprinfo_value, bool)'
+        try:
+            return frame.is_true(frame.eval(source,
+                                            __exprinfo_value=self.result))
+        except passthroughex:
+            raise
+        except:
+            return False
+
+    def eval(self, frame):
+        node = Interpretable(self.node)
+        node.eval(frame)
+        explanations = []
+        vars = {'__exprinfo_fn': node.result}
+        source = '__exprinfo_fn('
+        for a in self.args:
+            if isinstance(a, ast.Keyword):
+                keyword = a.name
+                a = a.expr
+            else:
+                keyword = None
+            a = Interpretable(a)
+            a.eval(frame)
+            argname = '__exprinfo_%d' % len(vars)
+            vars[argname] = a.result
+            if keyword is None:
+                source += argname + ','
+                explanations.append(a.explanation)
+            else:
+                source += '%s=%s,' % (keyword, argname)
+                explanations.append('%s=%s' % (keyword, a.explanation))
+        if self.star_args:
+            star_args = Interpretable(self.star_args)
+            star_args.eval(frame)
+            argname = '__exprinfo_star'
+            vars[argname] = star_args.result
+            source += '*' + argname + ','
+            explanations.append('*' + star_args.explanation)
+        if self.dstar_args:
+            dstar_args = Interpretable(self.dstar_args)
+            dstar_args.eval(frame)
+            argname = '__exprinfo_kwds'
+            vars[argname] = dstar_args.result
+            source += '**' + argname + ','
+            explanations.append('**' + dstar_args.explanation)
+        self.explanation = "%s(%s)" % (
+            node.explanation, ', '.join(explanations))
+        if source.endswith(','):
+            source = source[:-1]
+        source += ')'
+        try:
+            self.result = frame.eval(source, **vars)
+        except passthroughex:
+            raise
+        except:
+            raise Failure(self)
+        if not node.is_builtin(frame) or not self.is_bool(frame):
+            r = frame.repr(self.result)
+            self.explanation = '%s\n{%s = %s\n}' % (r, r, self.explanation)
+
+class Getattr(Interpretable):
+    __view__ = ast.Getattr
+
+    def eval(self, frame):
+        expr = Interpretable(self.expr)
+        expr.eval(frame)
+        source = '__exprinfo_expr.%s' % self.attrname
+        try:
+            self.result = frame.eval(source, __exprinfo_expr=expr.result)
+        except passthroughex:
+            raise
+        except:
+            raise Failure(self)
+        self.explanation = '%s.%s' % (expr.explanation, self.attrname)
+        # if the attribute comes from the instance, its value is interesting
+        source = ('hasattr(__exprinfo_expr, "__dict__") and '
+                  '%r in __exprinfo_expr.__dict__' % self.attrname)
+        try:
+            from_instance = frame.is_true(
+                frame.eval(source, __exprinfo_expr=expr.result))
+        except passthroughex:
+            raise
+        except:
+            from_instance = True
+        if from_instance:
+            r = frame.repr(self.result)
+            self.explanation = '%s\n{%s = %s\n}' % (r, r, self.explanation)
+
+# == Re-interpretation of full statements ==
+
+class Assert(Interpretable):
+    __view__ = ast.Assert
+
+    def run(self, frame):
+        test = Interpretable(self.test)
+        test.eval(frame)
+        # simplify 'assert False where False = ...'
+        if (test.explanation.startswith('False\n{False = ') and
+            test.explanation.endswith('\n}')):
+            test.explanation = test.explanation[15:-2]
+        # print the result as  'assert <explanation>'
+        self.result = test.result
+        self.explanation = 'assert ' + test.explanation
+        if not frame.is_true(test.result):
+            try:
+                raise BuiltinAssertionError
+            except passthroughex:
+                raise
+            except:
+                raise Failure(self)
+
+class Assign(Interpretable):
+    __view__ = ast.Assign
+
+    def run(self, frame):
+        expr = Interpretable(self.expr)
+        expr.eval(frame)
+        self.result = expr.result
+        self.explanation = '... = ' + expr.explanation
+        # fall-back-run the rest of the assignment
+        ass = ast.Assign(self.nodes, ast.Name('__exprinfo_expr'))
+        mod = ast.Module(None, ast.Stmt([ass]))
+        mod.filename = '<run>'
+        co = pycodegen.ModuleCodeGenerator(mod).getCode()
+        try:
+            frame.exec_(co, __exprinfo_expr=expr.result)
+        except passthroughex:
+            raise
+        except:
+            raise Failure(self)
+
+class Discard(Interpretable):
+    __view__ = ast.Discard
+
+    def run(self, frame):
+        expr = Interpretable(self.expr)
+        expr.eval(frame)
+        self.result = expr.result
+        self.explanation = expr.explanation
+
+class Stmt(Interpretable):
+    __view__ = ast.Stmt
+
+    def run(self, frame):
+        for stmt in self.nodes:
+            stmt = Interpretable(stmt)
+            stmt.run(frame)
+
+
+def report_failure(e):
+    explanation = e.node.nice_explanation()
+    if explanation:
+        explanation = ", in: " + explanation
+    else:
+        explanation = ""
+    sys.stdout.write("%s: %s%s\n" % (e.exc.__name__, e.value, explanation))
+
+def check(s, frame=None):
+    if frame is None:
+        frame = sys._getframe(1)
+        frame = py.code.Frame(frame)
+    expr = parse(s, 'eval')
+    assert isinstance(expr, ast.Expression)
+    node = Interpretable(expr.node)
+    try:
+        node.eval(frame)
+    except passthroughex:
+        raise
+    except Failure:
+        e = sys.exc_info()[1]
+        report_failure(e)
+    else:
+        if not frame.is_true(node.result):
+            sys.stderr.write("assertion failed: %s\n" % node.nice_explanation())
+
+
+###########################################################
+# API / Entry points
+# #########################################################
+
+def interpret(source, frame, should_fail=False):
+    module = Interpretable(parse(source, 'exec').node)
+    #print "got module", module
+    if isinstance(frame, py.std.types.FrameType):
+        frame = py.code.Frame(frame)
+    try:
+        module.run(frame)
+    except Failure:
+        e = sys.exc_info()[1]
+        return getfailure(e)
+    except passthroughex:
+        raise
+    except:
+        import traceback
+        traceback.print_exc()
+    if should_fail:
+        return ("(assertion failed, but when it was re-run for "
+                "printing intermediate values, it did not fail.  Suggestions: "
+                "compute assert expression before the assert or use --nomagic)")
+    else:
+        return None
+
+def getmsg(excinfo):
+    if isinstance(excinfo, tuple):
+        excinfo = py.code.ExceptionInfo(excinfo)
+    #frame, line = gettbline(tb)
+    #frame = py.code.Frame(frame)
+    #return interpret(line, frame)
+
+    tb = excinfo.traceback[-1]
+    source = str(tb.statement).strip()
+    x = interpret(source, tb.frame, should_fail=True)
+    if not isinstance(x, str):
+        raise TypeError("interpret returned non-string %r" % (x,))
+    return x
+
+def getfailure(e):
+    explanation = e.node.nice_explanation()
+    if str(e.value):
+        lines = explanation.split('\n')
+        lines[0] += "  << %s" % (e.value,)
+        explanation = '\n'.join(lines)
+    text = "%s: %s" % (e.exc.__name__, explanation)
+    if text.startswith('AssertionError: assert '):
+        text = text[16:]
+    return text
+
+def run(s, frame=None):
+    if frame is None:
+        frame = sys._getframe(1)
+        frame = py.code.Frame(frame)
+    module = Interpretable(parse(s, 'exec').node)
+    try:
+        module.run(frame)
+    except Failure:
+        e = sys.exc_info()[1]
+        report_failure(e)
+
+
+if __name__ == '__main__':
+    # example:
+    def f():
+        return 5
+    def g():
+        return 3
+    def h(x):
+        return 'never'
+    check("f() * g() == 5")
+    check("not f()")
+    check("not (f() and g() or 0)")
+    check("f() == g()")
+    i = 4
+    check("i == f()")
+    check("len(f()) == 0")
+    check("isinstance(2+3+4, float)")
+
+    run("x = i")
+    check("x == 5")
+
+    run("assert not f(), 'oops'")
+    run("a, b, c = 1, 2")
+    run("a, b, c = f()")
+
+    check("max([f(),g()]) == 4")
+    check("'hello'[g()] == 'h'")
+    run("'guk%d' % h(f())")
diff --git a/_pytest/assertion/reinterpret.py b/_pytest/assertion/reinterpret.py
new file mode 100644
index 000000000..6e9465d8a
--- /dev/null
+++ b/_pytest/assertion/reinterpret.py
@@ -0,0 +1,48 @@
+import sys
+import py
+
+BuiltinAssertionError = py.builtin.builtins.AssertionError
+
+class AssertionError(BuiltinAssertionError):
+    def __init__(self, *args):
+        BuiltinAssertionError.__init__(self, *args)
+        if args:
+            try:
+                self.msg = str(args[0])
+            except py.builtin._sysex:
+                raise
+            except:
+                self.msg = "<[broken __repr__] %s at %0xd>" %(
+                    args[0].__class__, id(args[0]))
+        else:
+            f = py.code.Frame(sys._getframe(1))
+            try:
+                source = f.code.fullsource
+                if source is not None:
+                    try:
+                        source = source.getstatement(f.lineno, assertion=True)
+                    except IndexError:
+                        source = None
+                    else:
+                        source = str(source.deindent()).strip()
+            except py.error.ENOENT:
+                source = None
+                # this can also occur during reinterpretation, when the
+                # co_filename is set to "<run>".
+            if source:
+                self.msg = reinterpret(source, f, should_fail=True)
+            else:
+                self.msg = "<could not determine information>"
+            if not self.args:
+                self.args = (self.msg,)
+
+if sys.version_info > (3, 0):
+    AssertionError.__module__ = "builtins"
+    reinterpret_old = "old reinterpretation not available for py3"
+else:
+    from _pytest.assertion.oldinterpret import interpret as reinterpret_old
+if sys.version_info >= (2, 6) or (sys.platform.startswith("java")):
+    from _pytest.assertion.newinterpret import interpret as reinterpret
+else:
+    reinterpret = reinterpret_old
+
diff --git a/_pytest/assertion/rewrite.py b/_pytest/assertion/rewrite.py
index 29ce43869..186d2425e 100644
--- a/_pytest/assertion/rewrite.py
+++ b/_pytest/assertion/rewrite.py
@@ -13,7 +13,6 @@ def rewrite_asserts(mod):
 
 
 _saferepr = py.io.saferepr
-_format_explanation = py.code._format_explanation
 
 def _format_boolop(operands, explanations, is_or):
     show_explanations = []
@@ -31,8 +30,9 @@ def _call_reprcompare(ops, results, expls, each_obj):
             done = True
         if done:
             break
-    if py.code._reprcompare is not None:
-        custom = py.code._reprcompare(ops[i], each_obj[i], each_obj[i + 1])
+    from _pytest.assertion import _reprcompare
+    if _reprcompare is not None:
+        custom = _reprcompare(ops[i], each_obj[i], each_obj[i + 1])
         if custom is not None:
             return custom
     return expl
@@ -94,7 +94,7 @@ class AssertionRewriter(ast.NodeVisitor):
         # Insert some special imports at the top of the module but after any
         # docstrings and __future__ imports.
         aliases = [ast.alias(py.builtin.builtins.__name__, "@py_builtins"),
-                   ast.alias("py", "@pylib"),
+                   ast.alias("_pytest.assertion", "@pytest_a"),
                    ast.alias("_pytest.assertion.rewrite", "@pytest_ar")]
         expect_docstring = True
         pos = 0
@@ -153,11 +153,11 @@ class AssertionRewriter(ast.NodeVisitor):
 
     def display(self, expr):
         """Call py.io.saferepr on the expression."""
-        return self.helper("saferepr", expr)
+        return self.helper("ar", "saferepr", expr)
 
-    def helper(self, name, *args):
+    def helper(self, mod, name, *args):
         """Call a helper in this module."""
-        py_name = ast.Name("@pytest_ar", ast.Load())
+        py_name = ast.Name("@pytest_" + mod, ast.Load())
         attr = ast.Attribute(py_name, "_" + name, ast.Load())
         return ast.Call(attr, list(args), [], None, None)
 
@@ -211,7 +211,7 @@ class AssertionRewriter(ast.NodeVisitor):
         explanation = "assert " + explanation
         template = ast.Str(explanation)
         msg = self.pop_format_context(template)
-        fmt = self.helper("format_explanation", msg)
+        fmt = self.helper("a", "format_explanation", msg)
         body.append(ast.Assert(top_condition, fmt))
         # Delete temporary variables.
         names = [ast.Name(name, ast.Del()) for name in self.variables]
@@ -242,7 +242,7 @@ class AssertionRewriter(ast.NodeVisitor):
             explanations.append(explanation)
         expls = ast.Tuple([ast.Str(expl) for expl in explanations], ast.Load())
         is_or = ast.Num(isinstance(boolop.op, ast.Or))
-        expl_template = self.helper("format_boolop",
+        expl_template = self.helper("ar", "format_boolop",
                                     ast.Tuple(operands, ast.Load()), expls,
                                     is_or)
         expl = self.pop_format_context(expl_template)
@@ -321,7 +321,8 @@ class AssertionRewriter(ast.NodeVisitor):
             self.statements.append(ast.Assign([store_names[i]], res_expr))
             left_res, left_expl = next_res, next_expl
         # Use py.code._reprcompare if that's available.
-        expl_call = self.helper("call_reprcompare", ast.Tuple(syms, ast.Load()),
+        expl_call = self.helper("ar", "call_reprcompare",
+                                ast.Tuple(syms, ast.Load()),
                                 ast.Tuple(load_names, ast.Load()),
                                 ast.Tuple(expls, ast.Load()),
                                 ast.Tuple(results, ast.Load()))
diff --git a/testing/test_assertinterpret.py b/testing/test_assertinterpret.py
new file mode 100644
index 000000000..318516eae
--- /dev/null
+++ b/testing/test_assertinterpret.py
@@ -0,0 +1,327 @@
+"PYTEST_DONT_REWRITE"
+import pytest, py
+
+from _pytest import assertion
+
+def exvalue():
+    return py.std.sys.exc_info()[1]
+
+def f():
+    return 2
+
+def test_not_being_rewritten():
+    assert "@py_builtins" not in globals()
+
+def test_assert():
+    try:
+        assert f() == 3
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith('assert 2 == 3\n')
+
+def test_assert_with_explicit_message():
+    try:
+        assert f() == 3, "hello"
+    except AssertionError:
+        e = exvalue()
+        assert e.msg == 'hello'
+
+def test_assert_within_finally():
+    class A:
+        def f():
+            pass
+    excinfo = py.test.raises(TypeError, """
+        try:
+            A().f()
+        finally:
+            i = 42
+    """)
+    s = excinfo.exconly()
+    assert s.find("takes no argument") != -1
+
+    #def g():
+    #    A.f()
+    #excinfo = getexcinfo(TypeError, g)
+    #msg = getmsg(excinfo)
+    #assert msg.find("must be called with A") != -1
+
+
+def test_assert_multiline_1():
+    try:
+        assert (f() ==
+                3)
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith('assert 2 == 3\n')
+
+def test_assert_multiline_2():
+    try:
+        assert (f() == (4,
+                   3)[-1])
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith('assert 2 ==')
+
+def test_in():
+    try:
+        assert "hi" in [1, 2]
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith("assert 'hi' in")
+
+def test_is():
+    try:
+        assert 1 is 2
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith("assert 1 is 2")
+
+
+@py.test.mark.skipif("sys.version_info < (2,6)")
+def test_attrib():
+    class Foo(object):
+        b = 1
+    i = Foo()
+    try:
+        assert i.b == 2
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith("assert 1 == 2")
+
+@py.test.mark.skipif("sys.version_info < (2,6)")
+def test_attrib_inst():
+    class Foo(object):
+        b = 1
+    try:
+        assert Foo().b == 2
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith("assert 1 == 2")
+
+def test_len():
+    l = list(range(42))
+    try:
+        assert len(l) == 100
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert s.startswith("assert 42 == 100")
+        assert "where 42 = len([" in s
+
+def test_assert_non_string_message():
+    class A:
+        def __str__(self):
+            return "hello"
+    try:
+        assert 0 == 1, A()
+    except AssertionError:
+        e = exvalue()
+        assert e.msg == "hello"
+
+def test_assert_keyword_arg():
+    def f(x=3):
+        return False
+    try:
+        assert f(x=5)
+    except AssertionError:
+        e = exvalue()
+        assert "x=5" in e.msg
+
+# These tests should both fail, but should fail nicely...
+class WeirdRepr:
+    def __repr__(self):
+        return '<WeirdRepr\nsecond line>'
+
+def bug_test_assert_repr():
+    v = WeirdRepr()
+    try:
+        assert v == 1
+    except AssertionError:
+        e = exvalue()
+        assert e.msg.find('WeirdRepr') != -1
+        assert e.msg.find('second line') != -1
+        assert 0
+
+def test_assert_non_string():
+    try:
+        assert 0, ['list']
+    except AssertionError:
+        e = exvalue()
+        assert e.msg.find("list") != -1
+
+def test_assert_implicit_multiline():
+    try:
+        x = [1,2,3]
+        assert x != [1,
+           2, 3]
+    except AssertionError:
+        e = exvalue()
+        assert e.msg.find('assert [1, 2, 3] !=') != -1
+
+
+def test_assert_with_brokenrepr_arg():
+    class BrokenRepr:
+        def __repr__(self): 0 / 0
+    e = AssertionError(BrokenRepr())
+    if e.msg.find("broken __repr__") == -1:
+        py.test.fail("broken __repr__ not handle correctly")
+
+def test_multiple_statements_per_line():
+    try:
+        a = 1; assert a == 2
+    except AssertionError:
+        e = exvalue()
+        assert "assert 1 == 2" in e.msg
+
+def test_power():
+    try:
+        assert 2**3 == 7
+    except AssertionError:
+        e = exvalue()
+        assert "assert (2 ** 3) == 7" in e.msg
+
+
+class TestView:
+
+    def setup_class(cls):
+        cls.View = pytest.importorskip("_pytest.assertion.oldinterpret").View
+
+    def test_class_dispatch(self):
+        ### Use a custom class hierarchy with existing instances
+
+        class Picklable(self.View):
+            pass
+
+        class Simple(Picklable):
+            __view__ = object
+            def pickle(self):
+                return repr(self.__obj__)
+
+        class Seq(Picklable):
+            __view__ = list, tuple, dict
+            def pickle(self):
+                return ';'.join(
+                    [Picklable(item).pickle() for item in self.__obj__])
+
+        class Dict(Seq):
+            __view__ = dict
+            def pickle(self):
+                return Seq.pickle(self) + '!' + Seq(self.values()).pickle()
+
+        assert Picklable(123).pickle() == '123'
+        assert Picklable([1,[2,3],4]).pickle() == '1;2;3;4'
+        assert Picklable({1:2}).pickle() == '1!2'
+
+    def test_viewtype_class_hierarchy(self):
+        # Use a custom class hierarchy based on attributes of existing instances
+        class Operation:
+            "Existing class that I don't want to change."
+            def __init__(self, opname, *args):
+                self.opname = opname
+                self.args = args
+
+        existing = [Operation('+', 4, 5),
+                    Operation('getitem', '', 'join'),
+                    Operation('setattr', 'x', 'y', 3),
+                    Operation('-', 12, 1)]
+
+        class PyOp(self.View):
+            def __viewkey__(self):
+                return self.opname
+            def generate(self):
+                return '%s(%s)' % (self.opname, ', '.join(map(repr, self.args)))
+
+        class PyBinaryOp(PyOp):
+            __view__ = ('+', '-', '*', '/')
+            def generate(self):
+                return '%s %s %s' % (self.args[0], self.opname, self.args[1])
+
+        codelines = [PyOp(op).generate() for op in existing]
+        assert codelines == ["4 + 5", "getitem('', 'join')",
+            "setattr('x', 'y', 3)", "12 - 1"]
+
+@py.test.mark.skipif("sys.version_info < (2,6)")
+def test_assert_customizable_reprcompare(monkeypatch):
+    monkeypatch.setattr(assertion, '_reprcompare', lambda *args: 'hello')
+    try:
+        assert 3 == 4
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert "hello" in s
+
+def test_assert_long_source_1():
+    try:
+        assert len == [
+            (None, ['somet text', 'more text']),
+        ]
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert 're-run' not in s
+        assert 'somet text' in s
+
+def test_assert_long_source_2():
+    try:
+        assert(len == [
+            (None, ['somet text', 'more text']),
+        ])
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert 're-run' not in s
+        assert 'somet text' in s
+
+def test_assert_raise_alias(testdir):
+    testdir.makepyfile("""
+    "PYTEST_DONT_REWRITE"
+    import sys
+    EX = AssertionError
+    def test_hello():
+        raise EX("hello"
+            "multi"
+            "line")
+    """)
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines([
+        "*def test_hello*",
+        "*raise EX*",
+        "*1 failed*",
+    ])
+
+
+@pytest.mark.skipif("sys.version_info < (2,5)")
+def test_assert_raise_subclass():
+    class SomeEx(AssertionError):
+        def __init__(self, *args):
+            super(SomeEx, self).__init__()
+    try:
+        raise SomeEx("hello")
+    except AssertionError:
+        s = str(exvalue())
+        assert 're-run' not in s
+        assert 'could not determine' in s
+
+def test_assert_raises_in_nonzero_of_object_pytest_issue10():
+    class A(object):
+        def __nonzero__(self):
+            raise ValueError(42)
+        def __lt__(self, other):
+            return A()
+        def __repr__(self):
+            return "<MY42 object>"
+    def myany(x):
+        return True
+    try:
+        assert not(myany(A() < 0))
+    except AssertionError:
+        e = exvalue()
+        s = str(e)
+        assert "<MY42 object> < 0" in s
diff --git a/testing/test_assertion.py b/testing/test_assertion.py
index 567cebbf1..5470f6416 100644
--- a/testing/test_assertion.py
+++ b/testing/test_assertion.py
@@ -2,11 +2,12 @@ import sys
 
 import py, pytest
 import _pytest.assertion as plugin
+from _pytest.assertion import reinterpret
 
 needsnewassert = pytest.mark.skipif("sys.version_info < (2,6)")
 
 def interpret(expr):
-    return py.code._reinterpret(expr, py.code.Frame(sys._getframe(1)))
+    return reinterpret.reinterpret(expr, py.code.Frame(sys._getframe(1)))
 
 class TestBinReprIntegration:
     pytestmark = needsnewassert
@@ -25,7 +26,7 @@ class TestBinReprIntegration:
                 self.right = right
         mockhook = MockHook()
         monkeypatch = request.getfuncargvalue("monkeypatch")
-        monkeypatch.setattr(py.code, '_reprcompare', mockhook)
+        monkeypatch.setattr(plugin, '_reprcompare', mockhook)
         return mockhook
 
     def test_pytest_assertrepr_compare_called(self, hook):
@@ -40,13 +41,13 @@ class TestBinReprIntegration:
         assert hook.right == [0, 2]
 
     def test_configure_unconfigure(self, testdir, hook):
-        assert hook == py.code._reprcompare
+        assert hook == plugin._reprcompare
         config = testdir.parseconfig()
         plugin.pytest_configure(config)
-        assert hook != py.code._reprcompare
+        assert hook != plugin._reprcompare
         from _pytest.config import pytest_unconfigure
         pytest_unconfigure(config)
-        assert hook == py.code._reprcompare
+        assert hook == plugin._reprcompare
 
 def callequal(left, right):
     return plugin.pytest_assertrepr_compare('==', left, right)
diff --git a/testing/test_assertrewrite.py b/testing/test_assertrewrite.py
index 580eed420..d713b6e25 100644
--- a/testing/test_assertrewrite.py
+++ b/testing/test_assertrewrite.py
@@ -4,15 +4,16 @@ import pytest
 
 ast = pytest.importorskip("ast")
 
+from _pytest import assertion
 from _pytest.assertion.rewrite import rewrite_asserts
 
 
 def setup_module(mod):
-    mod._old_reprcompare = py.code._reprcompare
+    mod._old_reprcompare = assertion._reprcompare
     py.code._reprcompare = None
 
 def teardown_module(mod):
-    py.code._reprcompare = mod._old_reprcompare
+    assertion._reprcompare = mod._old_reprcompare
     del mod._old_reprcompare
 
 
@@ -229,13 +230,13 @@ class TestAssertionRewrite:
     def test_custom_reprcompare(self, monkeypatch):
         def my_reprcompare(op, left, right):
             return "42"
-        monkeypatch.setattr(py.code, "_reprcompare", my_reprcompare)
+        monkeypatch.setattr(assertion, "_reprcompare", my_reprcompare)
         def f():
             assert 42 < 3
         assert getmsg(f) == "assert 42"
         def my_reprcompare(op, left, right):
             return "%s %s %s" % (left, op, right)
-        monkeypatch.setattr(py.code, "_reprcompare", my_reprcompare)
+        monkeypatch.setattr(assertion, "_reprcompare", my_reprcompare)
         def f():
             assert 1 < 3 < 5 <= 4 < 7
         assert getmsg(f) == "assert 5 <= 4"