[BUG] Check environ before selecting a seed to prevent warning message

pytorch_lightning/utilities/seed.py

@@ -20,8 +20,8 @@
 
 import numpy as np
 import torch
-
 from pytorch_lightning import _logger as log
+from pytorch_lightning.utilities import rank_zero_warn
 
 
 def seed_everything(seed: Optional[int] = None) -> int:
@@ -41,18 +41,17 @@ def seed_everything(seed: Optional[int] = None) -> int:
 
     try:
         if seed is None:
-            seed = os.environ.get("PL_GLOBAL_SEED", _select_seed_randomly(min_seed_value, max_seed_value))
+            seed = os.environ.get("PL_GLOBAL_SEED")
         seed = int(seed)
     except (TypeError, ValueError):
         seed = _select_seed_randomly(min_seed_value, max_seed_value)
+        rank_zero_warn(f"No correct seed found, seed set to {seed}")
 
-    if (seed > max_seed_value) or (seed < min_seed_value):
-        log.warning(
-            f"{seed} is not in bounds, \
-            numpy accepts from {min_seed_value} to {max_seed_value}"
-        )
+    if not (min_seed_value <= seed <= max_seed_value):
+        rank_zero_warn(f"{seed} is not in bounds, numpy accepts from {min_seed_value} to {max_seed_value}")
         seed = _select_seed_randomly(min_seed_value, max_seed_value)
 
+    log.info(f"Global seed set to {seed}")
     os.environ["PL_GLOBAL_SEED"] = str(seed)
     random.seed(seed)
     np.random.seed(seed)
@@ -62,6 +61,4 @@ def seed_everything(seed: Optional[int] = None) -> int:
 
 
 def _select_seed_randomly(min_seed_value: int = 0, max_seed_value: int = 255) -> int:
-    seed = random.randint(min_seed_value, max_seed_value)
-    log.warning(f"No correct seed found, seed set to {seed}")
-    return seed
+    return random.randint(min_seed_value, max_seed_value)

tests/utilities/test_seed.py

@@ -0,0 +1,55 @@
+import os
+
+from unittest import mock
+import pytest
+
+import pytorch_lightning.utilities.seed as seed_utils
+
+
+@mock.patch.dict(os.environ, {}, clear=True)
+def test_seed_stays_same_with_multiple_seed_everything_calls():
+    """
+    Ensure that after the initial seed everything,
+    the seed stays the same for the same run.
+    """
+    with pytest.warns(UserWarning, match="No correct seed found"):
+        seed_utils.seed_everything()
+    initial_seed = os.environ.get("PL_GLOBAL_SEED")
+
+    with pytest.warns(None) as record:
+        seed_utils.seed_everything()
+    assert not record  # does not warn
+    seed = os.environ.get("PL_GLOBAL_SEED")
+
+    assert initial_seed == seed
+
+
+@mock.patch.dict(os.environ, {"PL_GLOBAL_SEED": "2020"}, clear=True)
+def test_correct_seed_with_environment_variable():
+    """
+    Ensure that the PL_GLOBAL_SEED environment is read
+    """
+    assert seed_utils.seed_everything() == 2020
+
+
+@mock.patch.dict(os.environ, {"PL_GLOBAL_SEED": "invalid"}, clear=True)
+@mock.patch.object(seed_utils, attribute='_select_seed_randomly', new=lambda *_: 123)
+def test_invalid_seed():
+    """
+    Ensure that we still fix the seed even if an invalid seed is given
+    """
+    with pytest.warns(UserWarning, match="No correct seed found"):
+        seed = seed_utils.seed_everything()
+    assert seed == 123
+
+
+@mock.patch.dict(os.environ, {}, clear=True)
+@mock.patch.object(seed_utils, attribute='_select_seed_randomly', new=lambda *_: 123)
+@pytest.mark.parametrize("seed", (10e9, -10e9))
+def test_out_of_bounds_seed(seed):
+    """
+    Ensure that we still fix the seed even if an out-of-bounds seed is given
+    """
+    with pytest.warns(UserWarning, match="is not in bounds"):
+        actual = seed_utils.seed_everything(seed)
+    assert actual == 123