I'm trying to figure out what this code does:
printdead, printlive = '_#'
It's from here, a site with implementations of elementary cellular automata: https://rosettacode.org/wiki/One-dimensional_cellular_automata#Python
Apparently I can replace the above statement by simply writing
printdead = '_'
printlive = '#'
printdead = '_'; printlive = '#'
printdead, printlive = '_', '#'
which is all perfectly fine by me. But how does the first statement work?
It's called iterable unpacking. If the right hand side of an assignment is an iterable object, you can unpack the values into different names. Strings, lists and tuples are just a few examples of iterables in Python.
>>> a, b, c = '123'
>>> a, b, c
('1', '2', '3')
>>> a, b, c = [1, 2, 3]
>>> a, b, c
(1, 2, 3)
>>> a, b, c = (1, 2, 3)
>>> a, b, c
(1, 2, 3)
If you are using Python 3, you have access to Extended Iterable Unpacking which allows you to use one wildcard in the assignment.
>>> a, *b, c = 'test123'
>>> a, b, c
('t', ['e', 's', 't', '1', '2'], '3')
>>> head, *tail = 'test123'
>>> head
't'
>>> tail
['e', 's', 't', '1', '2', '3']
You are correct.
The first statement will split the string given as input in one character strings and unpack the list. Therefore with this syntax you need as many variables in the left hand side expression as characters in your string.
strcan be treated as a sequence and is unpacked.'_##'would have resulted in an error. The same happens withfor char in string:.