MAINT: use RandomState._bit_generator directly

Author: andyfaff

numpy/random/_generator.pyi

@@ -17,7 +17,7 @@ from numpy import (
     uint32,
     uint64,
 )
-from numpy.random import BitGenerator, SeedSequence
+from numpy.random import BitGenerator, SeedSequence, RandomState
 from numpy._typing import (
     ArrayLike,
     NDArray,
@@ -782,5 +782,5 @@ class Generator:
     def shuffle(self, x: ArrayLike, axis: int = ...) -> None: ...
 
 def default_rng(
-    seed: None | _ArrayLikeInt_co | SeedSequence | BitGenerator | Generator = ...
+    seed: None | _ArrayLikeInt_co | SeedSequence | BitGenerator | Generator | RandomState = ...
 ) -> Generator: ...

numpy/random/_generator.pyx

@@ -5073,11 +5073,7 @@ def default_rng(seed=None):
         # Pass through a Generator.
         return seed
     elif isinstance(seed, np.random.RandomState):
-        rs_state = seed.get_state(legacy=False)
-        klass = getattr(np.random, rs_state['bit_generator'])
-        bg = klass()
-        bg.state = rs_state
-        gen = np.random.Generator(bg)
+        gen = np.random.Generator(seed._bit_generator)
         return gen
 
     # Otherwise we need to instantiate a new BitGenerator and Generator as

numpy/random/tests/test_direct.py

@@ -565,16 +565,15 @@ def test_coercion_RandomState_Generator(self):
         rs = RandomState(1234)
         rg = default_rng(rs)
         assert isinstance(rg.bit_generator, MT19937)
-
-        assert_allclose(rg.random(), rs.rand())
+        assert rg.bit_generator is rs._bit_generator
 
         # RandomState with a non MT19937 bit generator
         _original = np.random.get_bit_generator()
         bg = PCG64(12342298)
         np.random.set_bit_generator(bg)
         rs = np.random.mtrand._rand
         rg = default_rng(rs)
-        assert_allclose(rg.random(), rs.rand())
+        assert rg.bit_generator is bg
 
         # vital to get global state back to original, otherwise
         # other tests start to fail.