add python version.

snail.py

@@ -0,0 +1,53 @@
+def snail(xss):
+    h = len(xss)
+    w = len(xss[0])
+
+    if h == 0 or w == 0:
+        return []
+
+    v = []
+
+    for b in range(0, max(w, h) + 1):
+        ex = w - b - 1
+        ey = h - b - 1
+
+        for c in range(b, ex+1):
+            v.append(xss[b][c])
+        for r in range(b+1, ey+1):
+            v.append(xss[r][ex])
+
+        if ex == b or ey == b:
+            return v
+
+        for c in range(ex-1, b-1, -1):
+            v.append(xss[ey][c])
+        for r in range(ey-1, b, -1):
+            v.append(xss[r][b])
+
+    return v
+
+initial = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
+expected = [1, 2, 3, 6, 9, 8, 7, 4, 5]
+
+assert(snail(initial) == expected)
+print(snail(initial) == expected)
+
+initial = [[1,2,3,4], [5,6,7,8], [9,10,11,12]]
+expected = [1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7]
+
+assert(snail(initial) == expected)
+print(snail(initial) == expected)
+
+initial = [
+    [1, 2, 3], 
+    [4, 5, 6], 
+    [7, 8, 9], 
+    [10, 11, 12], 
+    [13, 14, 15]
+]
+expected = [1, 2, 3, 6, 9, 12, 15, 14, 13, 10, 7, 4, 5, 8, 11]
+
+assert(snail(initial) == expected)
+print(snail(initial) == expected)
+
+print("all tests passed")