Hello,there is a regression in the beta (alpha 4 was ok) for this kind of code:print("Complex call with both invalid star list and star arguments:")try:    a = 1    b = 2.0    functionWithDefaults(1,c = 3,*a,**b)except TypeError as e:    print(repr(e))try:    a = 1    b = 2.0    functionWithDefaults(1,*a,**b)except TypeError as e:    print(repr(e))try:    a = 1    b = 2.0    functionWithDefaults(c = 1, *a,**b)except TypeError as e:    print(repr(e))try:    a = 1    b = 2.0    functionWithDefaults(*a,**b)except TypeError as e:    print(repr(e))This prints with beta1 3.6Complex call with both invalid star list and star arguments:TypeError("'int' object is not iterable",)TypeError("'int' object is not iterable",)TypeError("'float' object is not iterable",)TypeError('functionWithDefaults() argument after ** must be a mapping, not float',)The later message is what they all probably should be like. This is 3.5 output:Complex call with both invalid star list and star arguments:TypeError('functionWithDefaults() argument after ** must be a mapping, not float',)TypeError('functionWithDefaults() argument after ** must be a mapping, not float',)TypeError('functionWithDefaults() argument after ** must be a mapping, not float',)TypeError('functionWithDefaults() argument after ** must be a mapping, not float',)The function itself doesn't matter obviously, it's never called. Please restore the old behavior, thanks.Yours,Kay

This is a consequence ofissue27213. Actually there are two issues: with var-positional and var-keyword arguments.But Python 3.5 is not consistent. It raises an exception with less detailed message if there are multiple var-positional or var-keyword arguments.Var-positional arguments:>>> f(*0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after * must be an iterable, not int>>> f(1, *0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after * must be an iterable, not int>>> f(*[], *0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not iterablePython 3.6 just raises the latter message in case of positional arguments and single var-positional argument.>>> f(*0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after * must be an iterable, not int>>> f(1, *0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not iterable>>> f(*[], *0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not iterableThis issue can't be fixed without adding new bytecode (BUILD_TUPLE_UNPACK_WITH_CALL). If it will be decided to fix it in 3.6, it may be worth to backport this to 3.5.Var-keyword arguments:Python 3.5:>>> f(**[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not list>>> f(x=1, **0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not int>>> f(x=1, **[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not list>>> f(**{}, **0)   Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not iterable>>> f(**{}, **[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'list' object is not a mappingPython 3.6 raises less detailed error message in case of keyword arguments and single var-keyword argument.>>> f(**0)                      Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not int>>> f(**[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not list>>> f(x=1, **0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not iterable>>> f(x=1, **[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'list' object is not a mapping>>> f(**{}, **0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not a mapping>>> f(**{}, **[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'list' object is not a mappingThis issue can be fixed without changing bytecode. The patch faster_build_map_unpack_with_call.patch forissue27358 fixes it.

Ned and Larry.Is it allowed to use the patch fromissue27358 for fixing a regression in 3.6 and inconsistency in 3.5 for var-keyword arguments? The patch introduces new private function _PyDict_MergeEx() and touches the implementation of PyDict_Merge(). Maybe this can be fixed with smaller patch, but I don't know.Is it allowed to add new opcode BUILD_TUPLE_UNPACK_WITH_CALL for fixing a regression in 3.6 and inconsistency in 3.5 for var-positional arguments? This is the only way. The bytecode already was changed in a bugfix release of 3.5 for more serious need: fixing potential segfault or security issue (issue27286).

It's too late to change this for 3.5.

That is a fairly big change to go in now but the error message regression is also big.  With a review from a core developer and assuming no other objections, I think this can go into 360b2.

> It's too late to change this for 3.5.The whole point of having a beta release is to detect issues like this.

Raymond, Larry's comment was about 3.5, not 3.6.  See my comment above.

Proposed patch fixes error message for var-positional arguments. It adds new opcode BUILD_TUPLE_UNPACK_WITH_CALL.>>> min(1, *2)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: min() argument after * must be an iterable, not int>>> min(*[1], *2)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: min() argument after * must be an iterable, not int

New changeset88b319dfc909 by Serhiy Storchaka in branch '3.6':Issue#28257: Improved error message when pass a non-iterable ashttps://hg.python.org/cpython/rev/88b319dfc909New changesetbde594cd8369 by Serhiy Storchaka in branch 'default':Issue#28257: Improved error message when pass a non-iterable ashttps://hg.python.org/cpython/rev/bde594cd8369New changeset40d7ce58ebd0 by Serhiy Storchaka in branch '3.5':Issue#28257: Backported a test.https://hg.python.org/cpython/rev/40d7ce58ebd0New changeseta8168a52a56f by Serhiy Storchaka in branch '2.7':Issue#28257: Backported a test.https://hg.python.org/cpython/rev/a8168a52a56f

Here is a patch with smaller (in comparison withissue27358) change for 3.5 that improves error message when pass a non-mapping as second var-keyword argument.Unpatched:>>> f(**{'a': 1}, **[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'list' object is not a mapping>>> f(**{'a': 1}, **0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: 'int' object is not iterablePatched:>>> f(**{'a': 1}, **[])Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not list>>> f(**{'a': 1}, **0)Traceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: f() argument after ** must be a mapping, not int

New changeset35676cd72352 by Serhiy Storchaka in branch '3.5':Issue#28257: Improved error message when pass a non-mapping as a var-keywordhttps://hg.python.org/cpython/rev/35676cd72352