add the infrastructure for the first backend

eth_hash/__init__.py

@@ -0,0 +1 @@
+from .main import Keccak256  # noqa: F401

eth_hash/auto.py

@@ -0,0 +1,4 @@
+from .main import Keccak256
+from .backends import pycryptodome
+
+keccak = Keccak256(pycryptodome)

eth_hash/backends/pycryptodome.py

@@ -0,0 +1,2 @@
+def keccak256(prehash):
+    return b''

eth_hash/main.py

@@ -0,0 +1,10 @@
+class Keccak256:
+    def __init__(self, backend):
+        self.hasher = backend.keccak256
+        # TODO run assertion to validate hash once on load, after first backend set up
+
+    def __call__(self, preimage):
+        if not isinstance(preimage, bytes):
+            raise TypeError("Can only compute the hash of a `bytes` value, not %r" % preimage)
+
+        return self.hasher(preimage)

tests/core/test_results.py

@@ -0,0 +1,20 @@
+import pytest
+
+
+@pytest.fixture
+def keccak():
+    from eth_hash.auto import keccak
+    return keccak
+
+
+@pytest.mark.parametrize(
+    'prehash, expected_result',
+    (
+        (
+            b'',
+            b"\xc5\xd2F\x01\x86\xf7#<\x92~}\xb2\xdc\xc7\x03\xc0\xe5\x00\xb6S\xca\x82';{\xfa\xd8\x04]\x85\xa4p",  # noqa: E501
+        ),
+    ),
+)
+def test_keccak_256(keccak, prehash, expected_result):
+    assert keccak(prehash) == expected_result