This is a consequence of issue27213. 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 iterable
Python 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 iterable
This 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 mapping
Python 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 mapping
This issue can be fixed without changing bytecode. The patch faster_build_map_unpack_with_call.patch for issue27358 fixes it.