Extended tuple unpacking in Python 2

Question

Is it possible to simulate extended tuple unpacking in Python 2?

Specifically, I have a for loop:

for a, b, c in mylist: 

which works fine when mylist is a list of tuples of size three. I want the same for loop to work if I pass in a list of size four.

I think I will end up using named tuples, but I was wondering if there is an easy way to write:

for a, b, c, *d in mylist: 

so that d eats up any extra members.

Answer 1

You can't do that directly, but it isn't terribly difficult to write a utility function to do this:

>>> def unpack_list(a, b, c, *d): ...   return a, b, c, d ...  >>> unpack_list(*range(100)) (0, 1, 2, (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99)) 

You could apply it to your for loop like this:

for sub_list in mylist:     a, b, c, d = unpack_list(*sub_list) 

Answer 2

You could define a wrapper function that converts your list to a four tuple. For example:

def wrapper(thelist):     for item in thelist:         yield(item[0], item[1], item[2], item[3:])  mylist = [(1,2,3,4), (5,6,7,8)]  for a, b, c, d in wrapper(mylist):     print a, b, c, d 

The code prints:

1 2 3 (4,) 5 6 7 (8,)