Fix numpy ValueError with seeds < 0 or > 2 ** 32 - 1 (#275)

Fixes #269

HISTORY.rst

@@ -2,6 +2,9 @@
 History
 -------
 
+* Fix numpy error ``ValueError: Seed must be between 0 and 2**32 - 1`` when
+  passed a seed outside of this range.
+
 3.4.0 (2020-05-27)
 ------------------
 

src/pytest_randomly.py

@@ -1,4 +1,5 @@
 import argparse
+import hashlib
 import random
 import sys
 
@@ -140,11 +141,12 @@ def _reseed(config, offset=0):
         faker_random.setstate(random_states[seed])
 
     if have_numpy:
-        if seed not in np_random_states:
-            np_random.seed(seed)
-            np_random_states[seed] = np_random.get_state()
+        numpy_seed = _truncate_seed_for_numpy(seed)
+        if numpy_seed not in np_random_states:
+            np_random.seed(numpy_seed)
+            np_random_states[numpy_seed] = np_random.get_state()
         else:
-            np_random.set_state(np_random_states[seed])
+            np_random.set_state(np_random_states[numpy_seed])
 
     if entrypoint_reseeds is None:
         entrypoint_reseeds = [
@@ -154,6 +156,15 @@ def _reseed(config, offset=0):
         reseed(seed)
 
 
+def _truncate_seed_for_numpy(seed):
+    seed = abs(seed)
+    if seed <= 2 ** 32 - 1:
+        return seed
+
+    seed_bytes = seed.to_bytes(seed.bit_length(), "big")
+    return int.from_bytes(hashlib.sha512(seed_bytes).digest()[: 32 // 8], "big")
+
+
 def pytest_report_header(config):
     seed = config.getoption("randomly_seed")
     _reseed(config)

tests/test_pytest_randomly.py

@@ -625,6 +625,20 @@ def test_two():
     out.assert_outcomes(passed=2)
 
 
+def test_numpy_doesnt_crash_with_large_seed(ourtestdir):
+    ourtestdir.makepyfile(
+        test_one="""
+        import numpy as np
+
+        def test_one():
+            assert np.random.rand() >= 0.0
+        """
+    )
+
+    out = ourtestdir.runpytest("--randomly-seed=7106521602475165645")
+    out.assert_outcomes(passed=1)
+
+
 def test_failing_import(testdir):
     """Test with pytest raising CollectError or ImportError.