[FrozenLake] Add seed in random map generation (openai#139)

gymnasium/envs/toy_text/frozen_lake.py

@@ -9,6 +9,7 @@
 from gymnasium import Env, spaces, utils
 from gymnasium.envs.toy_text.utils import categorical_sample
 from gymnasium.error import DependencyNotInstalled
+from gymnasium.utils import seeding
 
 LEFT = 0
 DOWN = 1
@@ -51,22 +52,27 @@ def is_valid(board: List[List[str]], max_size: int) -> bool:
     return False
 
 
-def generate_random_map(size: int = 8, p: float = 0.8) -> List[str]:
+def generate_random_map(
+    size: int = 8, p: float = 0.8, seed: Optional[int] = None
+) -> List[str]:
     """Generates a random valid map (one that has a path from start to goal)
 
     Args:
         size: size of each side of the grid
         p: probability that a tile is frozen
+        seed: optional seed to ensure the generation of reproducible maps
 
     Returns:
         A random valid map
     """
     valid = False
     board = []  # initialize to make pyright happy
 
+    np_random, _ = seeding.np_random(seed)
+
     while not valid:
         p = min(1, p)
-        board = np.random.choice(["F", "H"], (size, size), p=[p, 1 - p])
+        board = np_random.choice(["F", "H"], (size, size), p=[p, 1 - p])
         board[0][0] = "S"
         board[-1][-1] = "G"
         valid = is_valid(board, size)

tests/envs/test_env_implementation.py

@@ -126,6 +126,16 @@ def test_frozenlake_dfs_map_generation(map_size: int):
     raise AssertionError("No path through the frozenlake was found.")
 
 
+@pytest.mark.parametrize("map_size, seed", [(5, 123), (10, 42), (16, 987)])
+def test_frozenlake_map_generation_with_seed(map_size: int, seed: int):
+    map1 = generate_random_map(size=map_size, seed=seed)
+    map2 = generate_random_map(size=map_size, seed=seed)
+    assert map1 == map2
+    map1 = generate_random_map(size=map_size, seed=seed)
+    map2 = generate_random_map(size=map_size, seed=seed + 1)
+    assert map1 != map2
+
+
 def test_taxi_action_mask():
     env = TaxiEnv()