Add method BaseModel.hashes().

Can be useful to deduplicate code in swh-storage.

swh/model/model.py

@@ -384,6 +384,10 @@ class BaseContent(BaseModel):
             raise ValueError('{} is not a valid hash name.'.format(hash_name))
         return getattr(self, hash_name)
 
+    def hashes(self) -> Dict[str, bytes]:
+        """Returns a dictionary {hash_name: hash_value}"""
+        return {algo: getattr(self, algo) for algo in DEFAULT_ALGORITHMS}
+
 
 @attr.s(frozen=True)
 class Content(BaseContent):

swh/model/tests/test_model.py

@@ -62,6 +62,13 @@ def test_content_get_hash():
         assert c.get_hash(hash_name) == hash_
 
 
+def test_content_hashes():
+    hashes = dict(
+        sha1=b'foo', sha1_git=b'bar', sha256=b'baz', blake2s256=b'qux')
+    c = Content(length=42, status='visible', **hashes)
+    assert c.hashes() == hashes
+
+
 def test_directory_model_id_computation():
     dir_dict = dict(directory_example)
     del dir_dict['id']