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random_utils.py

@@ -1,50 +1,34 @@
-import contextlib
+import hashlib
 import random as python_random
-import string
-import threading
 
 __default_seed__ = 42
-_thread_local = threading.local()
 
-
-def get_seed():
-    try:
-        return _thread_local.seed
-    except AttributeError:
-        _thread_local.seed = __default_seed__
-        return _thread_local.seed
-
-
-def get_random():
-    try:
-        return _thread_local.random
-    except AttributeError:
-        _thread_local.random = python_random.Random(get_seed())
-        return _thread_local.random
-
-
-random = get_random()
+from typing import Any, Hashable
 
 
-def set_seed(seed):
-    _thread_local.seed = seed
-    get_random().seed(seed)
-
-
-def get_random_string(length):
-    letters = string.ascii_letters
-    return "".join(get_random().choice(letters) for _ in range(length))
-
-
-@contextlib.contextmanager
-def nested_seed(sub_seed=None):
-    old_state = get_random().getstate()
-    old_global_seed = get_seed()
-    sub_seed = sub_seed or get_random_string(10)
-    new_global_seed = str(old_global_seed) + "/" + sub_seed
-    set_seed(new_global_seed)
-    try:
-        yield get_random()
-    finally:
-        set_seed(old_global_seed)
-        get_random().setstate(old_state)
+def get_seed():
+    return __default_seed__
+
+
+def new_random_generator(sub_seed: Any) -> python_random.Random:
+    """Get a generator based on a seed derived from the default seed.
+
+    The purpose is to have a random generator that provides outputs
+    that are independent of previous randomizations.
+    """
+    if not isinstance(sub_seed, Hashable):
+        # e.g. for lists or dicts
+        # Create a persistent hash for the input object (using plain hash(..) produces
+        # a value that varies between runs)
+        sub_seed_str = str(sub_seed).encode("utf-8")
+        # limit the hash int size to 2^32
+        sub_seed_hexdigest = hashlib.md5(sub_seed_str).hexdigest()[:8]
+        # convert to int, from base 16:
+        sub_seed_int = int(sub_seed_hexdigest, 16)
+        sub_seed = str(sub_seed_int)
+    elif not isinstance(sub_seed, str):
+        # for Hashable objects that are not strings
+        sub_seed = str(hash(sub_seed))
+
+    sub_default_seed = str(__default_seed__) + "/" + sub_seed
+    return python_random.Random(sub_default_seed)