Pattern matching of lists in Python

Question

I want to do some pattern matching on lists in Python. For example, in Haskell, I can do something like the following:

fun (head : rest) = ...

So when I pass in a list, head will be the first element, and rest will be the trailing elements.

Likewise, in Python, I can automatically unpack tuples:

(var1, var2) = func_that_returns_a_tuple()

I want to do something similar with lists in Python. Right now, I have a function that returns a list, and a chunk of code that does the following:

ls = my_func()
(head, rest) = (ls[0], ls[1:])

I wondered if I could somehow do that in one line in Python, instead of two.

Answer 1

So far as I know there's no way to make it a one-liner in current Python without introducing another function, e.g.:

split_list = lambda lst: (lst[0], lst[1:])
head, rest = split_list(my_func())

However, in Python 3.0 the specialized syntax used for variadic argument signatures and argument unpacking will become available for this type of general sequence unpacking as well, so in 3.0 you'll be able to write:

head, *rest = my_func()

See PEP 3132 for details.