SyntaxError in variable unpacking

[slozier]

for x, *y in (enumerate(range(5))): pass

SyntaxError: invalid syntax

[hackf5]

This behaviour is described in PEP 3132 -- Extended Iterable Unpacking. The example given in this document is:

for a, *b in [(1, 2, 3), (4, 5, 6, 7)]:
    print("a={0}, b={1}".format(a, b))

a=1, b=[2, 3]
a=4, b=[5, 6, 7]

[slozier]

Probably also of interest: https://github.com/IronLanguages/ironpython3/blob/master/Src/StdLib/Lib/test/test_unpack_ex.py

Edit: although it doesn't seem to throw a SyntaxError so it might not cover this case.

[hackf5]

Here are some more from test_unpack_ex.py

Case 1

Expected

[a, *b, c] = range(5)
print("a={0}, b={1}, c={2}".format(a, b, c))

a=0, b=[1, 2, 3], c=4

Actual

>>> [a, *b, c] = range(5)
  File "<stdin>", line 1
    [a, *b, c] = range(5)
        ^
SyntaxError: invalid syntax

Case 2

Expected

a, *b, c, *d, e = range(10)

SyntaxError: two starred expressions in assignment

Actual

>>> a, *b, c, *d, e = range(10)
>>> a
0
>>> b
[1, 2, 3, 4, 5, 6]
>>> c
7
>>> d
8
>>> e
9

Case 3

Expected

*a = range(10)

SyntaxError: starred assignment target must be in a list or tuple

Actual

>>> *a = range(10)
>>> a
range(0, 10)

Case 4

Expected

a* = range(10)
a*

    a* = range(10)
       ^
SyntaxError: invalid syntax

Actual

>>> a = range(1)
>>> *a
range(0, 1)

Case 5

Expected

*1

SyntaxError: can't use starred expression here

Actual

>>> *1
1

Notes

There are a couple more failures in there, but they look like they are possibly handled by other cases, or they are valid but different messages for example a, *b, c = [1] gives an equivalent error message.

[hackf5]

This library astpretty runs in IronPython3 and it is quite useful.

[hackf5]

The grammar definition for 3.4.10 is here: https://github.com/python/cpython/blob/v3.4.10/Grammar/Grammar