Implement JSON as an adapter on the PackageMetadata object, simplifying the experience for the consumer.

Author: jaraco

importlib_metadata/__init__.py

@@ -5,7 +5,6 @@
 import sys
 import zipp
 import email
-import string
 import pathlib
 import operator
 import textwrap
@@ -16,10 +15,10 @@
 import contextlib
 import collections
 
+from . import _adapters, _meta
 from ._collections import FreezableDefaultDict, Pair
 from ._compat import (
     NullFinder,
-    Protocol,
     PyPy_repr,
     install,
 )
@@ -30,7 +29,7 @@
 from importlib import import_module
 from importlib.abc import MetaPathFinder
 from itertools import starmap
-from typing import Any, List, Mapping, Optional, TypeVar, Union
+from typing import List, Mapping, Optional, Union
 
 
 __all__ = [
@@ -394,25 +393,6 @@ def __repr__(self):
         return '<FileHash mode: {} value: {}>'.format(self.mode, self.value)
 
 
-_T = TypeVar("_T")
-
-
-class PackageMetadata(Protocol):
-    def __len__(self) -> int:
-        ...  # pragma: no cover
-
-    def __contains__(self, item: str) -> bool:
-        ...  # pragma: no cover
-
-    def __getitem__(self, key: str) -> str:
-        ...  # pragma: no cover
-
-    def get_all(self, name: str, failobj: _T = ...) -> Union[List[Any], _T]:
-        """
-        Return all values associated with a possibly multi-valued key.
-        """
-
-
 class Distribution:
     """A Python distribution package."""
 
@@ -497,7 +477,7 @@ def _local(cls, root='.'):
         return PathDistribution(zipp.Path(meta.build_as_zip(builder)))
 
     @property
-    def metadata(self) -> PackageMetadata:
+    def metadata(self) -> _meta.PackageMetadata:
         """Return the parsed metadata for this Distribution.
 
         The returned object will have keys that name the various bits of
@@ -511,7 +491,7 @@ def metadata(self) -> PackageMetadata:
             # (which points to the egg-info file) attribute unchanged.
             or self.read_text('')
         )
-        return email.message_from_string(text)
+        return _adapters.JSONMeta(email.message_from_string(text))
 
     @property
     def name(self):
@@ -843,7 +823,7 @@ def distributions(**kwargs):
     return Distribution.discover(**kwargs)
 
 
-def metadata(distribution_name) -> PackageMetadata:
+def metadata(distribution_name) -> _meta.PackageMetadata:
     """Get the metadata for the named package.
 
     :param distribution_name: The name of the distribution package to query.
@@ -920,43 +900,3 @@ def packages_distributions() -> Mapping[str, List[str]]:
         for pkg in (dist.read_text('top_level.txt') or '').split():
             pkg_to_dist[pkg].append(dist.metadata['Name'])
     return dict(pkg_to_dist)
-
-
-def as_json(metadata: PackageMetadata):
-    """
-    Convert PackageMetadata to a JSON-compatible format
-    per PEP 0566.
-    """
-    # TODO: Need to match case-insensitive
-    multiple_use = {
-        'Classifier',
-        'Obsoletes-Dist',
-        'Platform',
-        'Project-URL',
-        'Provides-Dist',
-        'Provides-Extra',
-        'Requires-Dist',
-        'Requires-External',
-        'Supported-Platform',
-    }
-
-    def redent(value):
-        "Correct for RFC822 indentation"
-        if not value or '\n' not in value:
-            return value
-        return textwrap.dedent(' ' * 8 + value)
-
-    def transform(key):
-        value = (
-            metadata.get_all(key) if key in multiple_use else redent(metadata.get(key))
-        )
-        if key == 'Keywords':
-            value = value.split(string.whitespace)
-        if not value and key == 'Description':
-            value = metadata.get_payload()
-        tk = key.lower().replace('-', '_')
-        return tk, value
-
-    desc = ['Description'] if metadata.get_payload() else []  # type: ignore
-    keys = itertools.chain(metadata, desc)  # type: ignore
-    return dict(map(transform, keys))  # type: ignore

importlib_metadata/_adapters.py

@@ -0,0 +1,66 @@
+import string
+import textwrap
+import itertools
+
+from . import _meta
+
+
+class JSONMeta(_meta.PackageMetadata):
+    def __init__(self, orig: _meta.PackageMetadata):
+        self.orig = orig
+
+    def __getitem__(self, item):
+        return self.orig.__getitem__(item)
+
+    def __len__(self):
+        return self.orig.__len__()  # pragma: nocover
+
+    def __contains__(self, item):
+        return self.orig.__contains__(item)  # pragma: nocover
+
+    def __iter__(self):
+        return self.orig.__iter__()
+
+    def get_all(self, name):
+        return self.orig.get_all(name)
+
+    def get_payload(self):
+        return self.orig.get_payload()
+
+    @property
+    def json(self):
+        """
+        Convert PackageMetadata to a JSON-compatible format
+        per PEP 0566.
+        """
+        # TODO: Need to match case-insensitive
+        multiple_use = {
+            'Classifier',
+            'Obsoletes-Dist',
+            'Platform',
+            'Project-URL',
+            'Provides-Dist',
+            'Provides-Extra',
+            'Requires-Dist',
+            'Requires-External',
+            'Supported-Platform',
+        }
+
+        def redent(value):
+            "Correct for RFC822 indentation"
+            if not value or '\n' not in value:
+                return value
+            return textwrap.dedent(' ' * 8 + value)
+
+        def transform(key):
+            value = self.get_all(key) if key in multiple_use else redent(self[key])
+            if key == 'Keywords':
+                value = value.split(string.whitespace)
+            if not value and key == 'Description':
+                value = self.get_payload()
+            tk = key.lower().replace('-', '_')
+            return tk, value
+
+        desc = ['Description'] if self.get_payload() else []
+        keys = itertools.chain(self, desc)
+        return dict(map(transform, keys))

importlib_metadata/_meta.py

@@ -0,0 +1,24 @@
+from ._compat import Protocol
+from typing import Any, List, TypeVar, Union
+
+
+_T = TypeVar("_T")
+
+
+class PackageMetadata(Protocol):
+    def __len__(self) -> int:
+        ...  # pragma: no cover
+
+    def __contains__(self, item: str) -> bool:
+        ...  # pragma: no cover
+
+    def __getitem__(self, key: str) -> str:
+        ...  # pragma: no cover
+
+    def get_payload(self) -> str:
+        ...  # pragma: no cover
+
+    def get_all(self, name: str, failobj: _T = ...) -> Union[List[Any], _T]:
+        """
+        Return all values associated with a possibly multi-valued key.
+        """

tests/test_api.py

@@ -8,7 +8,6 @@
 from importlib_metadata import (
     Distribution,
     PackageNotFoundError,
-    as_json,
     distribution,
     entry_points,
     files,
@@ -248,13 +247,13 @@ def test_more_complex_deps_requires_text(self):
         assert deps == expected
 
     def test_as_json(self):
-        md = as_json(metadata('distinfo-pkg'))
+        md = metadata('distinfo-pkg').json
         assert 'name' in md
         desc = md['description']
         assert desc.startswith('Once upon a time\nThere was')
 
     def test_as_json_egg_info(self):
-        md = as_json(metadata('egginfo-pkg'))
+        md = metadata('egginfo-pkg').json
         assert 'name' in md
         desc = md['description']
         assert desc.startswith('Once upon a time\nThere was')