Given two strings, how do I assign the shorter string to one variable and the longer string to another

Sorting seems a bit overkill. You can do it in one line just with if.

x,y = (a,b) if len(a) < len(b) else (b,a)

x = min(a, b, key=len)
y = max(a, b, key=len)

Repetition, but intention is clear.

Edit:

Removed parentheses that makes tuples out of a and b since min and max takes in variable number of arguments.

Found one way.

(x,y) = sorted([a,b], key = len)

Use min(n1, n2, n3, ...)

>>> n1 = "abcdefghijkl"
>>> n2 = "abc"
>>> min((n1,n2), key=len)
'abc'
>>> max((n1,n2), key=len)
'abcdefghijkl'

You can use sequence unpacking with min / max. This is still O(n) complexity, albeit a 2-pass solution, which doesn't involve creating an intermediary list or tuple of strings.

a = 'hello'
b = 'test'

x, y = (func(a, b, key=len) for func in (min, max))

print(x, y, sep='\n')

# test
# hello

Here's a functional version:

from operator import methodcaller

x, y = map(methodcaller('__call__', a, b, key=len), (min, max))

The question seems really opinion-based, and for this reason I think we should define beautiful referring to the Zen of Python, in particular:

Flat is better than nested.
Sparse is better than dense.
Readability counts.

For these reasons, I think that your approach:

if len(a) > len(b) :
    (x,y) = (b,a)
else:
    (x,y) = (a,b)

is the best one.

Just a demo how dict can also be used

Solution 1:

a = [3]
b = [2,3 ]

_bool = len(a)<len(b)

d = { True : a, False : b}

x = d[_bool]
y = d[not _bool]


print(x, y)

Using Lists:

Solution 2:

x, y = [[a, b], [b, a]][len(a) > len(b)]

Although my preferred approach is

x, y = sorted([a, b], key=len)