Add migration script

migrations/convert_cache_to_dataclass_v1.py

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+#!/usr/bin/env python3
+"""Convert original cache file(simple dict) to data class v1."""
+import argparse
+import logging
+import pickle
+import shutil
+import sys
+from dataclasses import dataclass, field
+
+
+@dataclass
+class CachedData:
+    """CachedData represents locally cached data and state."""
+
+    items: dict = field(default_factory=dict)
+
+
+def main():
+    """Open cache file, convert it and overwrite it.
+
+    Backup file is created in the process. Manual cleanup is required after
+    migration.
+    """
+    logging.basicConfig(stream=sys.stdout)
+    logger = logging.getLogger('migrate-to-dataclass')
+    args = parse_args()
+    if args.verbosity:
+        logger.setLevel(logging.DEBUG)
+
+    logger.info("Read cache from file '%s'.", args.cache)
+    with open(args.cache, 'rb') as fhandle:
+        cache = pickle.load(fhandle)
+
+    if not isinstance(cache, dict):
+        logger.error(
+            "Cache file '%s' has invalid format, dict is expected.", args.cache
+        )
+        sys.exit(1)
+
+    bak_file = '{}.bak'.format(args.cache)
+    logger.info("Create backup file '%s' from '%s'.", bak_file, args.cache)
+    shutil.copy2(args.cache, bak_file)
+
+    new_cache = CachedData()
+    for key, value in cache.items():
+        new_cache.items[key] = value
+
+    logger.info("Write converted cache into file '%s'.", args.cache)
+    with open(args.cache, 'wb') as fhandle:
+        pickle.dump(new_cache, fhandle, pickle.HIGHEST_PROTOCOL)
+
+    logger.info("Migration complete and '%s' can be removed.", bak_file)
+
+
+def parse_args() -> argparse.Namespace:
+    """Return parsed CLI args."""
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        '-v', '--verbose',
+        dest='verbosity', action='store_true', default=False,
+        help='Increase logging verbosity.'
+    )
+    parser.add_argument(
+        '--cache',
+        dest='cache', type=str, default=None, required=True,
+        help='File which contains cache.'
+    )
+    return parser.parse_args()
+
+
+if __name__ == '__main__':
+    main()

migrations/tests/test_convert_cache_to_dataclass_v1.py

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+#!/usr/bin/env python3
+"""Unit tests for convert_cache_to_dataclass_v1.py."""
+import io
+import os
+import pickle
+import sys
+from unittest.mock import patch
+
+import pytest
+
+import migrations.convert_cache_to_dataclass_v1 as migration  # noqa:I202
+
+
+@pytest.fixture
+def fixture_bak_cleanup():
+    """Cleanup bak file which is created during migration."""
+    bak_fnames = []
+
+    def _fixture_back_cleanup(bak_fname):
+        bak_fnames.append(bak_fname)
+        return bak_fname
+
+    yield _fixture_back_cleanup
+
+    for bak_fname in bak_fnames:
+        print("teardown of '{}'".format(bak_fname))
+        os.remove(bak_fname)
+
+
+def test_migration(fixture_cache_file, fixture_bak_cleanup):
+    """Test migration under ideal conditions."""
+    bak_file = '{}.bak'.format(fixture_cache_file)
+    _ = fixture_bak_cleanup(bak_file)
+    expected_cache = migration.CachedData(
+        items={
+            'test1': 1234,
+            'test2': 0,
+        }
+    )
+
+    test_data = {
+        'test1': 1234,
+        'test2': 0,
+    }
+    with open(fixture_cache_file, 'wb') as fhandle:
+        pickle.dump(test_data, fhandle, pickle.HIGHEST_PROTOCOL)
+
+    exception = None
+    args = [
+        './convert_cache_to_dataclass_v1.py',
+        '--cache',
+        fixture_cache_file,
+    ]
+
+    saved_stdout = sys.stdout
+    out = io.StringIO()
+    sys.stdout = out
+
+    with patch.object(sys, 'argv', args):
+        try:
+            migration.main()
+        except Exception as exc:
+            exception = exc
+        finally:
+            sys.stdout = saved_stdout
+
+    assert exception is None
+    assert os.path.exists(bak_file) is True
+
+    with open(fixture_cache_file, 'rb') as fhandle:
+        migrated_cache = pickle.load(fhandle)
+    assert migrated_cache == expected_cache