https://www.codewars.com/kata/521c2db8ddc89b9b7a0000c1/

snail.py

def snail(snail_map):
    s = snail_map
    n = len(s)

    l = []
    if n > 1:
        for i in range(n):
            l.append(s[0][i])
        for i in range(1, n-1):
            l.append(s[i][n-1])
        for i in range(n-1, -1, -1):
            l.append(s[n-1][i])
        for i in range(n-2, 0, -1):
            l.append(s[i][0])
        
        s = [s[i][1:n-1] for i in range(n) if i != 0 and i != n-1]
        
        return l + snail(s)

    elif n == 1:
        if len(s[0]) > 0:
            return [s[0][0]]
        else: # This happens only in the case that s = [[]]
            return []

    else: # n == 0
        return l # l = []