Tuple extraction in lambda isn't supported with more than one argument.

Python 2.7 and earlier are in bug-fix mode (means no new features)
Tuple unpacking is not there in Python 3.
Please close this bug as invalid.

Works for me (Python 2.7.3):

>>> x = lambda (a, b), c: a + b + c
>>> x((2, 3), 4)
9

What issue are you seeing?

The issue is in lib2to3. tuple_params does not work with lambdas. I confirm the bug.

$ ./python -m lib2to3 -f tuple_params lambda_tuple_params.py 
RefactoringTool: Refactored lambda_tuple_params.py
--- lambda_tuple_params.py      (original)
+++ lambda_tuple_params.py      (refactored)
@@ -1,3 +1,3 @@
 lambda (a, b), c: a + b + c
-def f((a, b), c): return a + b + c
+def f(xxx_todo_changeme, c): (a, b) = xxx_todo_changeme; return a + b + c
 
RefactoringTool: Files that need to be modified:
RefactoringTool: lambda_tuple_params.py

I'm not sure a semantically neutral automatic fix is possible:

   f = lambda (a, b), c: a + b + c         # Py2.x

   f = lambda t, c: t[0] + t[1] + c        # Py3.x


The former will unpack any iterable, not just sequences:

    >>> def g():
	yield 'a'
	yield 'b'	
    >>> f(g(), 'c')
    'abc'

Also, the former will validate the number of arguments:

    >>> f((1,2,3), 4)

    Traceback (most recent call last):
      File "<pyshell#11>", line 1, in <module>
        f((1,2,3), 4)
      File "<pyshell#0>", line 1, in <lambda>
        f = lambda (a, b), c: a + b + c
    ValueError: too many values to unpack

I don't see a way to automatically include those capabilities in an automatic 2-to-3 transformation.

f = lambda t, c, *, _f=(lambda a, b, c: a + b + c): _f(*(unpack_tuple(2, t) + (c,)))

def unpack_tuple(n, t):
    t = tuple(t)
    if len(t) > n:
        raise ValueError('too many values to unpack (expected %d)' % (n,))
    if len(t) < n:
        raise ValueError('need more than %d values to unpack' % (len(t),))
    return t

Not pretty :-)

IMO, we're better off leaving 2-to-3 without an automated conversion for this and people will just have to stop using the feature in their 2.7 code.

We could add a -3 warning in Py2.7 to flag code that needs to be changed.

Updating the versions, but from the discussion I think this can probably be closed as "won't fix".