diff --git a/test_libs/pyspec/eth2spec/utils/hash_function.py b/test_libs/pyspec/eth2spec/utils/hash_function.py
index 4aecc57f8..2c9b5a579 100644
--- a/test_libs/pyspec/eth2spec/utils/hash_function.py
+++ b/test_libs/pyspec/eth2spec/utils/hash_function.py
@@ -2,18 +2,27 @@ from hashlib import sha256
 
 ZERO_BYTES32 = b'\x00' * 32
 
+
 def _hash(x):
     return sha256(x).digest()
 
-zerohashes = [(None, ZERO_BYTES32)]
-for layer in range(1, 32):
-    k = zerohashes[layer - 1][1] + zerohashes[layer - 1][1]
-    zerohashes.append((k, _hash(k)))
-zerohashes = zerohashes[1:]
+
+# Minimal collection of (key, value) pairs, for fast hash-retrieval, to save on repetitive computation cost.
+# Key = the hash input
+# Value = the hash output
+hash_cache = []
+
+
+def add_zero_hashes_to_cache():
+    zerohashes = [(None, ZERO_BYTES32)]
+    for layer in range(1, 32):
+        k = zerohashes[layer - 1][1] + zerohashes[layer - 1][1]
+        zerohashes.append((k, _hash(k)))
+    hash_cache.extend(zerohashes[1:])
 
 
 def hash(x):
-    for (k, h) in zerohashes:
+    for (k, h) in hash_cache:
         if x == k:
             return h
     return _hash(x)