A few minor tweaks now that we're on Python 3.8 (#890)

Originally this PR was running `pyupgrade --py38-plus` on the
codebase, to pick up a few new features in Python 3.7 and 3.8
(apart from f-strings, which was done in
#889). However, in
particular we didn't like how it converted `TypedDict` to the class
syntax, because then half of them were converted (the ones without
`-` in the field names can't be converted). So avoid that so they're
all consistent.

This includes:

* Use of set literals and comprehensions instead of set(...)
* Use OSError instead of IOError as the latter is now an alias
* Use b'' instead of bytes()
* One use of f-string that apparently flynt didn't pick up

This PR also:

* Removes the tox 4.2.8 pinning now that
  tox-dev/tox#2863 is fixed.
* Makes tox.ini source vars relative to fix autopep8 problem

.github/workflows/framework-tests.yaml

@@ -12,7 +12,7 @@ jobs:
         uses: actions/setup-python@v2
 
       - name: Install tox
-        run: pip install tox==4.2.8
+        run: pip install tox
 
       - name: Run linting
         run: tox -e lint
@@ -26,7 +26,7 @@ jobs:
         uses: actions/setup-python@v2
 
       - name: Install tox
-        run: pip install tox==4.2.8
+        run: pip install tox
 
       - name: Run static type checks
         run: tox -e static
@@ -47,7 +47,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Install tox
-        run: pip install tox==4.2.8
+        run: pip install tox
 
       - name: Run unit tests
         run: tox -e unit
@@ -73,7 +73,7 @@ jobs:
           go-version: "1.17"
 
       - name: Install tox
-        run: pip install tox==4.2.8
+        run: pip install tox
 
       - name: Install Pebble
         run: go install github.com/canonical/pebble/cmd/pebble@latest

.github/workflows/observability-charm-tests.yaml

@@ -25,7 +25,7 @@ jobs:
           echo -e "\ngit+$GITHUB_SERVER_URL/$GITHUB_REPOSITORY@$GITHUB_SHA#egg=ops" >> requirements.txt
 
       - name: Install dependencies
-        run: pip install tox==4.2.8
+        run: pip install tox
 
       - name: Run the charm tests
         run: tox -vve unit

ops/_private/yaml.py

@@ -23,9 +23,9 @@
 _safe_dumper = getattr(yaml, 'CSafeDumper', yaml.SafeDumper)
 
 
-def safe_load(stream: Union[str, TextIO]):
+def safe_load(stream: Union[str, TextIO]) -> Any:
     """Same as yaml.safe_load, but use fast C loader if available."""
-    return yaml.load(stream, Loader=_safe_loader)
+    return yaml.load(stream, Loader=_safe_loader)  # type: ignore
 
 
 @overload
@@ -40,4 +40,4 @@ def safe_dump(data: Any, stream: Optional[Union[str, TextIO]] = None, **kwargs:
 
     If `encoding:str` is provided, return bytes. Else, return str.
     """
-    return yaml.dump(data, stream=stream, Dumper=_safe_dumper, **kwargs)
+    return yaml.dump(data, stream=stream, Dumper=_safe_dumper, **kwargs)  # type: ignore

ops/charm.py

@@ -1195,7 +1195,7 @@ def __init__(self, role: RelationRole, relation_name: str, raw: '_RelationMetaDi
         self.scope = raw.get('scope') or self._default_scope
         if self.scope not in self.VALID_SCOPES:
             raise TypeError("scope should be one of {}; not '{}'".format(
-                ', '.join("'{}'".format(s) for s in self.VALID_SCOPES), self.scope))
+                ', '.join(f"'{s}'" for s in self.VALID_SCOPES), self.scope))
 
 
 class StorageMeta:

ops/framework.py

@@ -50,8 +50,7 @@
 
 if TYPE_CHECKING:
     from pathlib import Path
-
-    from typing_extensions import Literal, Protocol, Type
+    from typing import Literal, Protocol, Type
 
     from ops.charm import CharmMeta
     from ops.model import JsonObject, Model, _ModelBackend
@@ -613,8 +612,10 @@ def __init__(self, storage: Union[SQLiteStorage, JujuStorage],
 
         # Parse the env var once, which may be used multiple times later
         debug_at = os.environ.get('JUJU_DEBUG_AT')
-        self._juju_debug_at = (set(x.strip() for x in debug_at.split(','))
-                               if debug_at else set())  # type: Set[str]
+        if debug_at:
+            self._juju_debug_at = {x.strip() for x in debug_at.split(',')}
+        else:
+            self._juju_debug_at: Set[str] = set()
 
     def set_breakpointhook(self):
         """Hook into sys.breakpointhook so the builtin breakpoint() works as expected.

ops/pebble.py

@@ -1486,7 +1486,7 @@ def _request_raw(
             try:
                 body = json.loads(e.read())  # type: Dict[str, Any]
                 message = body['result']['message']  # type: str
-            except (IOError, ValueError, KeyError) as e2:
+            except (OSError, ValueError, KeyError) as e2:
                 # Will only happen on read error or if Pebble sends invalid JSON.
                 body = {}  # type: Dict[str, Any]
                 message = f'{type(e2).__name__} - {e2}'

pyproject.toml

@@ -28,12 +28,12 @@ per-file-ignores = ["test/*:D100,D101,D102,D103,D104"]
 docstring-convention = "google"
 
 [tool.pyright]
-include = ["ops/jujuversion.py", "ops/log.py", "ops/model.py", "ops/version.py",
-    "ops/__init__.py", "ops/framework.py", "ops/pebble.py", "ops/charm.py",
-    "ops/storage.py", "ops/main.py", "ops/testing.py", "ops/_private/timeconv.py"]
+include = ["ops/*.py", "ops/_private/*.py"]
 pythonVersion = "3.8" # check no python > 3.8 features are used
 pythonPlatform = "All"
 typeCheckingMode = "strict"
 reportIncompatibleMethodOverride = false
 reportImportCycles = false
 reportTypeCommentUsage = false
+reportMissingModuleSource = false
+stubPath = ""

test/pebble_cli.py

@@ -151,7 +151,7 @@ def main():
             try:
                 with open(args.layer_path, encoding='utf-8') as f:
                     layer_yaml = f.read()
-            except IOError as e:
+            except OSError as e:
                 parser.error(f'cannot read layer YAML: {e}')
             client.add_layer(args.label, layer_yaml, combine=bool(args.combine))
             result = f'Layer {args.label!r} added successfully from {args.layer_path!r}'

test/test_framework.py

@@ -1233,11 +1233,11 @@ def test_mutable_types(self):
         ), (
             lambda: set(),
             'a',
-            set(['a']),
+            {'a'},
             lambda a, b: a.add(b),
             lambda res, expected_res: self.assertEqual(res, expected_res)
         ), (
-            lambda: set(['a']),
+            lambda: {'a'},
             'a',
             set(),
             lambda a, b: a.discard(b),

test/test_pebble.py

@@ -1178,7 +1178,7 @@ def test_multipart_parser(self):
 
                 def handle_header(data):
                     headers.append(bytes(data))
-                    bodies.append(bytes())
+                    bodies.append(b'')
                     bodies_done.append(False)
 
                 def handle_body(data, done=False):

tox.ini

@@ -6,8 +6,10 @@ skip_missing_interpreters = True
 envlist = lint, unit
 
 [vars]
-src_path = {toxinidir}/ops/
-tst_path = {toxinidir}/test/
+# These need to be relative paths because autopep8 doesn't handle absolute
+# paths with relative paths in "exclude" correctly.
+src_path = ops/
+tst_path = test/
 all_path = {[vars]src_path} {[vars]tst_path}
 
 [testenv]