Re-use ExceptionTrap for trapping exceptions.

Author: jaraco

importlib_metadata/__init__.py

@@ -35,6 +35,7 @@
     NullFinder,
     install,
 )
+from ._context import ExceptionTrap
 from ._functools import method_cache, noop, pass_none, passthrough
 from ._itertools import always_iterable, bucket, unique_everseen
 from ._meta import PackageMetadata, SimplePath
@@ -496,11 +497,9 @@ def _prefer_valid(dists: Iterable[Distribution]) -> Iterable[Distribution]:
         Ref python/importlib_resources#489.
         """
 
-        def has_metadata(dist: Distribution) -> bool:
-            with suppress(MetadataNotFound):
-                dist.metadata
-                return True
-            return False
+        has_metadata = ExceptionTrap(MetadataNotFound).passes(
+            lambda dist: dist.metadata
+        )
 
         buckets = bucket(dists, has_metadata)
         return itertools.chain(buckets[True], buckets[False])

importlib_metadata/_context.py

@@ -0,0 +1,118 @@
+from __future__ import annotations
+
+import functools
+import operator
+
+
+# from jaraco.context 6.1
+class ExceptionTrap:
+    """
+    A context manager that will catch certain exceptions and provide an
+    indication they occurred.
+
+    >>> with ExceptionTrap() as trap:
+    ...     raise Exception()
+    >>> bool(trap)
+    True
+
+    >>> with ExceptionTrap() as trap:
+    ...     pass
+    >>> bool(trap)
+    False
+
+    >>> with ExceptionTrap(ValueError) as trap:
+    ...     raise ValueError("1 + 1 is not 3")
+    >>> bool(trap)
+    True
+    >>> trap.value
+    ValueError('1 + 1 is not 3')
+    >>> trap.tb
+    <traceback object at ...>
+
+    >>> with ExceptionTrap(ValueError) as trap:
+    ...     raise Exception()
+    Traceback (most recent call last):
+    ...
+    Exception
+
+    >>> bool(trap)
+    False
+    """
+
+    exc_info = None, None, None
+
+    def __init__(self, exceptions=(Exception,)):
+        self.exceptions = exceptions
+
+    def __enter__(self):
+        return self
+
+    @property
+    def type(self):
+        return self.exc_info[0]
+
+    @property
+    def value(self):
+        return self.exc_info[1]
+
+    @property
+    def tb(self):
+        return self.exc_info[2]
+
+    def __exit__(self, *exc_info):
+        type = exc_info[0]
+        matches = type and issubclass(type, self.exceptions)
+        if matches:
+            self.exc_info = exc_info
+        return matches
+
+    def __bool__(self):
+        return bool(self.type)
+
+    def raises(self, func, *, _test=bool):
+        """
+        Wrap func and replace the result with the truth
+        value of the trap (True if an exception occurred).
+
+        First, give the decorator an alias to support Python 3.8
+        Syntax.
+
+        >>> raises = ExceptionTrap(ValueError).raises
+
+        Now decorate a function that always fails.
+
+        >>> @raises
+        ... def fail():
+        ...     raise ValueError('failed')
+        >>> fail()
+        True
+        """
+
+        @functools.wraps(func)
+        def wrapper(*args, **kwargs):
+            with ExceptionTrap(self.exceptions) as trap:
+                func(*args, **kwargs)
+            return _test(trap)
+
+        return wrapper
+
+    def passes(self, func):
+        """
+        Wrap func and replace the result with the truth
+        value of the trap (True if no exception).
+
+        First, give the decorator an alias to support Python 3.8
+        Syntax.
+
+        >>> passes = ExceptionTrap(ValueError).passes
+
+        Now decorate a function that always fails.
+
+        >>> @passes
+        ... def fail():
+        ...     raise ValueError('failed')
+
+        >>> fail()
+        False
+        """
+        return self.raises(func, _test=operator.not_)

newsfragments/+.removal.rst

@@ -1 +1,2 @@
 - Removed the internal ``md_none`` typing helper since ``Distribution.metadata`` now always returns ``PackageMetadata`` and raises ``MetadataNotFound`` when absent (python/cpython#143387).
+- Vendored ``ExceptionTrap`` from ``jaraco.context`` (as ``_context``) and now rely on its ``passes`` helper when checking for missing metadata, keeping behavior aligned without adding dependencies.