diff --git a/src/testdir/test87.ok b/src/testdir/test87.ok
index 7ddea8f..c42acdf 100644
--- a/src/testdir/test87.ok
+++ b/src/testdir/test87.ok
@@ -764,7 +764,7 @@
 d["a"] = {"abcF" : Mapping({"\0" : 1})}:(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using d["a"] = {"abcF" : %s}
-d["a"] = {"abcF" : FailingIter()}:(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d["a"] = {"abcF" : FailingIter()}:(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d["a"] = {"abcF" : FailingIterNext()}:(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d["a"] = {"abcF" : %s}
@@ -791,7 +791,7 @@
 d["a"] = Mapping({"abcG" : Mapping({"\0" : 1})}):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using d["a"] = Mapping({"abcG" : %s})
-d["a"] = Mapping({"abcG" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d["a"] = Mapping({"abcG" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d["a"] = Mapping({"abcG" : FailingIterNext()}):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d["a"] = Mapping({"abcG" : %s})
@@ -803,7 +803,7 @@
 d["a"] = Mapping({"abcG" : FailingNumber()}):(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using d["a"] = %s
-d["a"] = FailingIter():(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d["a"] = FailingIter():(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d["a"] = FailingIterNext():(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d["a"] = %s
@@ -840,7 +840,7 @@
 d.update({"abcF" : Mapping({"\0" : 1})}):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using d.update({"abcF" : %s})
-d.update({"abcF" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d.update({"abcF" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d.update({"abcF" : FailingIterNext()}):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update({"abcF" : %s})
@@ -867,7 +867,7 @@
 d.update(Mapping({"abcG" : Mapping({"\0" : 1})})):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using d.update(Mapping({"abcG" : %s}))
-d.update(Mapping({"abcG" : FailingIter()})):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d.update(Mapping({"abcG" : FailingIter()})):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d.update(Mapping({"abcG" : FailingIterNext()})):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update(Mapping({"abcG" : %s}))
@@ -911,7 +911,7 @@
 d.update((("a", {"abcF" : Mapping({"\0" : 1})}),)):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using d.update((("a", {"abcF" : %s}),))
-d.update((("a", {"abcF" : FailingIter()}),)):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d.update((("a", {"abcF" : FailingIter()}),)):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d.update((("a", {"abcF" : FailingIterNext()}),)):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update((("a", {"abcF" : %s}),))
@@ -938,7 +938,7 @@
 d.update((("a", Mapping({"abcG" : Mapping({"\0" : 1})})),)):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using d.update((("a", Mapping({"abcG" : %s})),))
-d.update((("a", Mapping({"abcG" : FailingIter()})),)):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d.update((("a", Mapping({"abcG" : FailingIter()})),)):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d.update((("a", Mapping({"abcG" : FailingIterNext()})),)):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update((("a", Mapping({"abcG" : %s})),))
@@ -950,7 +950,7 @@
 d.update((("a", Mapping({"abcG" : FailingNumber()})),)):(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using d.update((("a", %s),))
-d.update((("a", FailingIter()),)):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+d.update((("a", FailingIter()),)):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 d.update((("a", FailingIterNext()),)):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update((("a", %s),))
@@ -989,7 +989,7 @@
 vim.List([{"abcF" : Mapping({"\0" : 1})}]):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using vim.List([{"abcF" : %s}])
-vim.List([{"abcF" : FailingIter()}]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+vim.List([{"abcF" : FailingIter()}]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 vim.List([{"abcF" : FailingIterNext()}]):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using vim.List([{"abcF" : %s}])
@@ -1016,7 +1016,7 @@
 vim.List([Mapping({"abcG" : Mapping({"\0" : 1})})]):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using vim.List([Mapping({"abcG" : %s})])
-vim.List([Mapping({"abcG" : FailingIter()})]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+vim.List([Mapping({"abcG" : FailingIter()})]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 vim.List([Mapping({"abcG" : FailingIterNext()})]):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using vim.List([Mapping({"abcG" : %s})])
@@ -1028,7 +1028,7 @@
 vim.List([Mapping({"abcG" : FailingNumber()})]):(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using vim.List([%s])
-vim.List([FailingIter()]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+vim.List([FailingIter()]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 vim.List([FailingIterNext()]):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using vim.List([%s])
@@ -1074,7 +1074,7 @@
 l[:] = [{"abcF" : Mapping({"\0" : 1})}]:(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using l[:] = [{"abcF" : %s}]
-l[:] = [{"abcF" : FailingIter()}]:(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+l[:] = [{"abcF" : FailingIter()}]:(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 l[:] = [{"abcF" : FailingIterNext()}]:(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using l[:] = [{"abcF" : %s}]
@@ -1101,7 +1101,7 @@
 l[:] = [Mapping({"abcG" : Mapping({"\0" : 1})})]:(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using l[:] = [Mapping({"abcG" : %s})]
-l[:] = [Mapping({"abcG" : FailingIter()})]:(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+l[:] = [Mapping({"abcG" : FailingIter()})]:(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 l[:] = [Mapping({"abcG" : FailingIterNext()})]:(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using l[:] = [Mapping({"abcG" : %s})]
@@ -1113,7 +1113,7 @@
 l[:] = [Mapping({"abcG" : FailingNumber()})]:(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using l[:] = [%s]
-l[:] = [FailingIter()]:(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+l[:] = [FailingIter()]:(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 l[:] = [FailingIterNext()]:(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using l[:] = [%s]
@@ -1145,7 +1145,7 @@
 l.extend([{"abcF" : Mapping({"\0" : 1})}]):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using l.extend([{"abcF" : %s}])
-l.extend([{"abcF" : FailingIter()}]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+l.extend([{"abcF" : FailingIter()}]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 l.extend([{"abcF" : FailingIterNext()}]):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using l.extend([{"abcF" : %s}])
@@ -1172,7 +1172,7 @@
 l.extend([Mapping({"abcG" : Mapping({"\0" : 1})})]):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using l.extend([Mapping({"abcG" : %s})])
-l.extend([Mapping({"abcG" : FailingIter()})]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+l.extend([Mapping({"abcG" : FailingIter()})]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 l.extend([Mapping({"abcG" : FailingIterNext()})]):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using l.extend([Mapping({"abcG" : %s})])
@@ -1184,7 +1184,7 @@
 l.extend([Mapping({"abcG" : FailingNumber()})]):(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using l.extend([%s])
-l.extend([FailingIter()]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+l.extend([FailingIter()]):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 l.extend([FailingIterNext()]):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using l.extend([%s])
@@ -1210,7 +1210,7 @@
 vim.Function("xxx_non_existent_function_xxx4", args=[], self={}):(<class 'ValueError'>, ValueError('function xxx_non_existent_function_xxx4 does not exist',))
 >>> FunctionNew
 vim.Function("tr", self="abcFuncSelf"):(<class 'AttributeError'>, AttributeError('keys',))
-vim.Function("tr", args=427423):(<class 'TypeError'>, TypeError('unable to convert int to vim list',))
+vim.Function("tr", args=427423):(<class 'TypeError'>, TypeError('unable to convert int to a Vim list',))
 vim.Function("tr", self="abcFuncSelf2", args="abcFuncArgs2"):(<class 'AttributeError'>, AttributeError('keys',))
 vim.Function(self="abcFuncSelf2", args="abcFuncArgs2"):(<class 'AttributeError'>, AttributeError('keys',))
 vim.Function("tr", "", self="abcFuncSelf2", args="abcFuncArgs2"):(<class 'AttributeError'>, AttributeError('keys',))
@@ -1232,7 +1232,7 @@
 f({"abcF" : Mapping({"\0" : 1})}):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using f({"abcF" : %s})
-f({"abcF" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+f({"abcF" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 f({"abcF" : FailingIterNext()}):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using f({"abcF" : %s})
@@ -1259,7 +1259,7 @@
 f(Mapping({"abcG" : Mapping({"\0" : 1})})):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using f(Mapping({"abcG" : %s}))
-f(Mapping({"abcG" : FailingIter()})):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+f(Mapping({"abcG" : FailingIter()})):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 f(Mapping({"abcG" : FailingIterNext()})):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using f(Mapping({"abcG" : %s}))
@@ -1271,7 +1271,7 @@
 f(Mapping({"abcG" : FailingNumber()})):(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using f(%s)
-f(FailingIter()):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+f(FailingIter()):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 f(FailingIterNext()):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using f(%s)
@@ -1298,7 +1298,7 @@
 fd(self={"abcF" : Mapping({"\0" : 1})}):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using fd(self={"abcF" : %s})
-fd(self={"abcF" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+fd(self={"abcF" : FailingIter()}):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 fd(self={"abcF" : FailingIterNext()}):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using fd(self={"abcF" : %s})
@@ -1325,7 +1325,7 @@
 fd(self=Mapping({"abcG" : Mapping({"\0" : 1})})):(<class 'TypeError'>, TypeError('expected bytes with no null',))
 <<< Finished
 >>> Testing *Iter* using fd(self=Mapping({"abcG" : %s}))
-fd(self=Mapping({"abcG" : FailingIter()})):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim structure',))
+fd(self=Mapping({"abcG" : FailingIter()})):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim structure',))
 fd(self=Mapping({"abcG" : FailingIterNext()})):(<class 'NotImplementedError'>, NotImplementedError('next',))
 <<< Finished
 >>> Testing ConvertFromPyObject using fd(self=Mapping({"abcG" : %s}))
@@ -1337,16 +1337,16 @@
 fd(self=Mapping({"abcG" : FailingNumber()})):(<class 'NotImplementedError'>, NotImplementedError('int',))
 <<< Finished
 >>> Testing *Iter* using fd(self=%s)
-fd(self=FailingIter()):(<class 'TypeError'>, TypeError('unable to convert FailingIter to vim dictionary',))
-fd(self=FailingIterNext()):(<class 'TypeError'>, TypeError('unable to convert FailingIterNext to vim dictionary',))
+fd(self=FailingIter()):(<class 'TypeError'>, TypeError('unable to convert FailingIter to a Vim dictionary',))
+fd(self=FailingIterNext()):(<class 'TypeError'>, TypeError('unable to convert FailingIterNext to a Vim dictionary',))
 <<< Finished
 >>> Testing ConvertFromPyObject using fd(self=%s)
-fd(self=None):(<class 'TypeError'>, TypeError('unable to convert NoneType to vim dictionary',))
+fd(self=None):(<class 'TypeError'>, TypeError('unable to convert NoneType to a Vim dictionary',))
 fd(self={b"": 1}):(<class 'ValueError'>, ValueError('empty keys are not allowed',))
 fd(self={"": 1}):(<class 'ValueError'>, ValueError('empty keys are not allowed',))
 fd(self=FailingMapping()):(<class 'NotImplementedError'>, NotImplementedError('keys',))
 fd(self=FailingMappingKey()):(<class 'NotImplementedError'>, NotImplementedError('getitem:mappingkey',))
-fd(self=FailingNumber()):(<class 'TypeError'>, TypeError('unable to convert FailingNumber to vim dictionary',))
+fd(self=FailingNumber()):(<class 'TypeError'>, TypeError('unable to convert FailingNumber to a Vim dictionary',))
 <<< Finished
 >>> Testing ConvertFromPyMapping using fd(self=%s)
 fd(self=[]):(<class 'AttributeError'>, AttributeError('keys',))