Remove OrderedDict in favor of python3.7+ dict

After we drop support for python3.6 we can relly that dictionaries
preserve the insertion order:
https://docs.python.org/3.7/whatsnew/3.7.html

This means we can replace the usage of OrderedDict with a standard
dictionaries.

Something we have to keep in mind is that even thought the insertion
order is preserved the equality comparison for normal dicts is
insensitive for normal dicts compared to OrderedDict

For example:
>>> OrderedDict([(1,1), (2,2)]) == OrderedDict([(2,2), (1,1)])
False
>>> dict([(1,1), (2,2)]) == dict([(2,2), (1,1)])
True

Signed-off-by: Martin Vrachev <mvrachev@vmware.com>

examples/repo_example/basic_repo.py

@@ -25,7 +25,6 @@
 """
 import os
 import tempfile
-from collections import OrderedDict
 from datetime import datetime, timedelta
 from pathlib import Path
 from typing import Any, Dict
@@ -103,7 +102,7 @@ def _in(days: float) -> datetime:
     signed=Targets(
         version=1, spec_version=SPEC_VERSION, expires=_in(7), targets={}
     ),
-    signatures=OrderedDict(),
+    signatures={},
 )
 
 # For the purpose of this example we use the top-level targets role to protect
@@ -134,7 +133,7 @@ def _in(days: float) -> datetime:
         expires=_in(7),
         meta={"targets.json": MetaFile(version=1)},
     ),
-    OrderedDict(),
+    {},
 )
 
 # Timestamp (freshness)
@@ -156,7 +155,7 @@ def _in(days: float) -> datetime:
         expires=_in(1),
         snapshot_meta=MetaFile(version=1),
     ),
-    OrderedDict(),
+    {},
 )
 
 # Root (root of trust)
@@ -195,7 +194,7 @@ def _in(days: float) -> datetime:
         },
         consistent_snapshot=True,
     ),
-    signatures=OrderedDict(),
+    signatures={},
 )
 
 # NOTE: We only need the public part to populate root, so it is possible to use
@@ -292,7 +291,7 @@ def _in(days: float) -> datetime:
         expires=_in(7),
         targets={target_path: target_file_info},
     ),
-    signatures=OrderedDict(),
+    signatures={},
 )
 
 
@@ -313,20 +312,15 @@ def _in(days: float) -> datetime:
             keys[delegatee_name]
         )
     },
-    roles=OrderedDict(
-        [
-            (
-                delegatee_name,
-                DelegatedRole(
-                    name=delegatee_name,
-                    keyids=[keys[delegatee_name]["keyid"]],
-                    threshold=1,
-                    terminating=True,
-                    paths=["*.py"],
-                ),
-            )
-        ]
-    ),
+    roles={
+        delegatee_name: DelegatedRole(
+            name=delegatee_name,
+            keyids=[keys[delegatee_name]["keyid"]],
+            threshold=1,
+            terminating=True,
+            paths=["*.py"],
+        ),
+    },
 )
 
 # Remove target file info from top-level targets (delegatee is now responsible)

examples/repo_example/hashed_bin_delegation.py

@@ -19,7 +19,6 @@
 import hashlib
 import os
 import tempfile
-from collections import OrderedDict
 from datetime import datetime, timedelta
 from pathlib import Path
 from typing import Any, Dict, Iterator, List, Tuple
@@ -160,10 +159,10 @@ def find_hash_bin(path: str) -> str:
                     keys["bin-n"]
                 )
             },
-            roles=OrderedDict(),
+            roles={},
         ),
     ),
-    signatures=OrderedDict(),
+    signatures={},
 )
 
 # The hash bin generator yields an ordered list of incremental hash bin names
@@ -190,7 +189,7 @@ def find_hash_bin(path: str) -> str:
         signed=Targets(
             version=1, spec_version=SPEC_VERSION, expires=_in(7), targets={}
         ),
-        signatures=OrderedDict(),
+        signatures={},
     )
 
 # Add target file

tests/repository_simulator.py

@@ -47,7 +47,6 @@
 import logging
 import os
 import tempfile
-from collections import OrderedDict
 from dataclasses import dataclass, field
 from datetime import datetime, timedelta
 from typing import Dict, Iterator, List, Optional, Tuple
@@ -167,15 +166,15 @@ def _initialize(self) -> None:
         """Setup a minimal valid repository."""
 
         targets = Targets(1, SPEC_VER, self.safe_expiry, {}, None)
-        self.md_targets = Metadata(targets, OrderedDict())
+        self.md_targets = Metadata(targets, {})
 
         meta = {"targets.json": MetaFile(targets.version)}
         snapshot = Snapshot(1, SPEC_VER, self.safe_expiry, meta)
-        self.md_snapshot = Metadata(snapshot, OrderedDict())
+        self.md_snapshot = Metadata(snapshot, {})
 
         snapshot_meta = MetaFile(snapshot.version)
         timestamp = Timestamp(1, SPEC_VER, self.safe_expiry, snapshot_meta)
-        self.md_timestamp = Metadata(timestamp, OrderedDict())
+        self.md_timestamp = Metadata(timestamp, {})
 
         roles = {role_name: Role([], 1) for role_name in TOP_LEVEL_ROLE_NAMES}
         root = Root(1, SPEC_VER, self.safe_expiry, {}, roles, True)
@@ -185,7 +184,7 @@ def _initialize(self) -> None:
             root.add_key(role, key)
             self.add_signer(role, signer)
 
-        self.md_root = Metadata(root, OrderedDict())
+        self.md_root = Metadata(root, {})
         self.publish_root()
 
     def publish_root(self) -> None:
@@ -357,7 +356,7 @@ def add_delegation(
 
         # Create delegation
         if delegator.delegations is None:
-            delegator.delegations = Delegations({}, OrderedDict())
+            delegator.delegations = Delegations({}, {})
         # put delegation last by default
         delegator.delegations.roles[role.name] = role
 
@@ -368,7 +367,7 @@ def add_delegation(
 
         # Add metadata for the role
         if role.name not in self.md_delegates:
-            self.md_delegates[role.name] = Metadata(targets, OrderedDict())
+            self.md_delegates[role.name] = Metadata(targets, {})
 
     def write(self) -> None:
         """Dump current repository metadata to self.dump_dir

tuf/api/metadata.py

@@ -32,7 +32,6 @@
 import io
 import logging
 import tempfile
-from collections import OrderedDict
 from datetime import datetime
 from typing import (
     IO,
@@ -113,7 +112,7 @@ class Metadata(Generic[T]):
             signing the canonical serialized representation of 'signed'.
     """
 
-    def __init__(self, signed: T, signatures: "OrderedDict[str, Signature]"):
+    def __init__(self, signed: T, signatures: Dict[str, Signature]):
         self.signed: T = signed
         self.signatures = signatures
 
@@ -150,7 +149,7 @@ def from_dict(cls, metadata: Dict[str, Any]) -> "Metadata[T]":
             raise ValueError(f'unrecognized metadata type "{_type}"')
 
         # Make sure signatures are unique
-        signatures: "OrderedDict[str, Signature]" = OrderedDict()
+        signatures: Dict[str, Signature] = {}
         for sig_dict in metadata.pop("signatures"):
             sig = Signature.from_dict(sig_dict)
             if sig.keyid in signatures:
@@ -1211,7 +1210,7 @@ class Delegations:
     def __init__(
         self,
         keys: Dict[str, Key],
-        roles: "OrderedDict[str, DelegatedRole]",
+        roles: Dict[str, DelegatedRole],
         unrecognized_fields: Optional[Mapping[str, Any]] = None,
     ):
         self.keys = keys
@@ -1233,7 +1232,7 @@ def from_dict(cls, delegations_dict: Dict[str, Any]) -> "Delegations":
         for keyid, key_dict in keys.items():
             keys_res[keyid] = Key.from_dict(keyid, key_dict)
         roles = delegations_dict.pop("roles")
-        roles_res: "OrderedDict[str, DelegatedRole]" = OrderedDict()
+        roles_res: Dict[str, DelegatedRole] = {}
         for role_dict in roles:
             new_role = DelegatedRole.from_dict(role_dict)
             if new_role.name in roles_res: