feat: add curie method to NamespaceManager (#2365)

Added a `curie` method to `NamespaceManager`, which can be used to generate a
CURIE from a URI.

Other changes:

- Fixed `NamespaceManager.expand_curie` to work with CURIES that have blank
  prefixes (e.g. `:something`), which are valid according to [CURIE Syntax
  1.0](https://www.w3.org/TR/2010/NOTE-curie-20101216/).
- Added a test to confirm <#2077>.

Fixes <#2348>.

---------
Co-authored-by: Iwan Aucamp <aucampia@gmail.com>

rdflib/namespace/__init__.py

@@ -490,6 +490,35 @@ def qname(self, uri: str) -> str:
         else:
             return ":".join((prefix, name))
 
+    def curie(self, uri: str, generate: bool = True) -> str:
+        """
+        From a URI, generate a valid CURIE.
+
+        Result is guaranteed to contain a colon separating the prefix from the
+        name, even if the prefix is an empty string.
+
+        .. warning::
+
+            When ``generate`` is `True` (which is the default) and there is no
+            matching namespace for the URI in the namespace manager then a new
+            namespace will be added with prefix ``ns{index}``.
+
+            Thus, when ``generate`` is `True`, this function is not a pure
+            function because of this side-effect.
+
+            This default behaviour is chosen so that this function operates
+            similarly to `NamespaceManager.qname`.
+
+        :param uri: URI to generate CURIE for.
+        :param generate: Whether to add a prefix for the namespace if one doesn't
+            already exist.  Default: `True`.
+        :return: CURIE for the URI.
+        :raises KeyError: If generate is `False` and the namespace doesn't already have
+            a prefix.
+        """
+        prefix, namespace, name = self.compute_qname(uri, generate=generate)
+        return ":".join((prefix, name))
+
     def qname_strict(self, uri: str) -> str:
         prefix, namespace, name = self.compute_qname_strict(uri)
         if prefix == "":
@@ -643,7 +672,7 @@ def expand_curie(self, curie: str) -> URIRef:
         if not type(curie) is str:
             raise TypeError(f"Argument must be a string, not {type(curie).__name__}.")
         parts = curie.split(":", 1)
-        if len(parts) != 2 or len(parts[0]) < 1:
+        if len(parts) != 2:
             raise ValueError(
                 "Malformed curie argument, format should be e.g. “foaf:name”."
             )

test/test_namespace/test_namespacemanager.py

@@ -5,6 +5,7 @@
 import sys
 from contextlib import ExitStack
 from pathlib import Path
+from test.utils.exceptions import ExceptionChecker
 from typing import TYPE_CHECKING, Any, Dict, Mapping, Optional, Set, Tuple, Type, Union
 
 import pytest
@@ -484,3 +485,115 @@ def check() -> None:
     check()
     # Run a second time to check caching
     check()
+
+
+def make_test_nsm() -> NamespaceManager:
+    namespaces = [
+        ("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#"),
+        ("", "http://example.org/"),
+        (
+            # Because of <https://github.com/RDFLib/rdflib/issues/2077> this
+            # will have no effect on the namespace manager.
+            "eg",
+            "http://example.org/",
+        ),
+    ]
+    graph = Graph(bind_namespaces="none")
+    for prefix, namespace in namespaces:
+        graph.bind(prefix, namespace, override=False)
+
+    return graph.namespace_manager
+
+
+@pytest.fixture(scope="session")
+def test_nsm_session() -> NamespaceManager:
+    return make_test_nsm()
+
+
+@pytest.fixture(scope="function")
+def test_nsm_function() -> NamespaceManager:
+    return make_test_nsm()
+
+
+@pytest.mark.parametrize(
+    ["curie", "expected_result"],
+    [
+        ("rdf:type", "http://www.w3.org/1999/02/22-rdf-syntax-ns#type"),
+        (":foo", "http://example.org/foo"),
+        ("too_small", ExceptionChecker(ValueError, "Malformed curie argument")),
+        (
+            "egdo:bar",
+            ExceptionChecker(ValueError, 'Prefix "egdo" not bound to any namespace'),
+        ),
+        pytest.param(
+            "eg:foo",
+            "http://example.org/foo",
+            marks=pytest.mark.xfail(
+                raises=ValueError,
+                reason="This is failing because of https://github.com/RDFLib/rdflib/issues/2077",
+            ),
+        ),
+    ],
+)
+def test_expand_curie(
+    test_nsm_session: NamespaceManager,
+    curie: str,
+    expected_result: Union[ExceptionChecker, str],
+) -> None:
+    nsm = test_nsm_session
+    with ExitStack() as xstack:
+        if isinstance(expected_result, ExceptionChecker):
+            xstack.enter_context(expected_result)
+        result = nsm.expand_curie(curie)
+
+    if not isinstance(expected_result, ExceptionChecker):
+        assert URIRef(expected_result) == result
+
+
+@pytest.mark.parametrize(
+    ["uri", "generate", "expected_result"],
+    [
+        ("http://www.w3.org/1999/02/22-rdf-syntax-ns#type", None, "rdf:type"),
+        ("http://example.org/foo", None, ":foo"),
+        ("http://example.com/a#chair", None, "ns1:chair"),
+        ("http://example.com/a#chair", True, "ns1:chair"),
+        (
+            "http://example.com/a#chair",
+            False,
+            ExceptionChecker(
+                KeyError, "No known prefix for http://example.com/a# and generate=False"
+            ),
+        ),
+        ("http://example.com/b#chair", None, "ns1:chair"),
+        ("http://example.com/c", None, "ns1:c"),
+        ("", None, ExceptionChecker(ValueError, "Can't split ''")),
+        (
+            "http://example.com/",
+            None,
+            ExceptionChecker(ValueError, "Can't split 'http://example.com/'"),
+        ),
+    ],
+)
+def test_generate_curie(
+    test_nsm_function: NamespaceManager,
+    uri: str,
+    generate: Optional[bool],
+    expected_result: Union[ExceptionChecker, str],
+) -> None:
+    """
+    .. note::
+
+        This is using the function scoped nsm fixture because curie has side
+        effects and will modify the namespace manager.
+    """
+    nsm = test_nsm_function
+    with ExitStack() as xstack:
+        if isinstance(expected_result, ExceptionChecker):
+            xstack.enter_context(expected_result)
+        if generate is None:
+            result = nsm.curie(uri)
+        else:
+            result = nsm.curie(uri, generate=generate)
+
+    if not isinstance(expected_result, ExceptionChecker):
+        assert expected_result == result

test/utils/exceptions.py

@@ -1,15 +1,32 @@
+from __future__ import annotations
+
 import logging
 import re
 from dataclasses import dataclass
-from typing import Any, Dict, Optional, Pattern, Type, Union
+from types import TracebackType
+from typing import Any, ContextManager, Dict, Optional, Pattern, Type, Union
+
+import pytest
+from pytest import ExceptionInfo
 
 
-@dataclass(frozen=True)
-class ExceptionChecker:
+@dataclass
+class ExceptionChecker(ContextManager[ExceptionInfo[Exception]]):
     type: Type[Exception]
     pattern: Optional[Union[Pattern[str], str]] = None
     attributes: Optional[Dict[str, Any]] = None
 
+    def __post_init__(self) -> None:
+        self._catcher = pytest.raises(self.type, match=self.pattern)
+        self._exception_info: Optional[ExceptionInfo[Exception]] = None
+
+    def _check_attributes(self, exception: Exception) -> None:
+        if self.attributes is not None:
+            for key, value in self.attributes.items():
+                logging.debug("checking exception attribute %s=%r", key, value)
+                assert hasattr(exception, key)
+                assert getattr(exception, key) == value
+
     def check(self, exception: Exception) -> None:
         logging.debug("checking exception %s/%r", type(exception), exception)
         pattern = self.pattern
@@ -19,11 +36,22 @@ def check(self, exception: Exception) -> None:
             assert isinstance(exception, self.type)
             if pattern is not None:
                 assert pattern.match(f"{exception}")
-            if self.attributes is not None:
-                for key, value in self.attributes.items():
-                    logging.debug("checking exception attribute %s=%r", key, value)
-                    assert hasattr(exception, key)
-                    assert getattr(exception, key) == value
+            self._check_attributes(exception)
         except Exception:
             logging.error("problem checking exception", exc_info=exception)
             raise
+
+    def __enter__(self) -> ExceptionInfo[Exception]:
+        self._exception_info = self._catcher.__enter__()
+        return self._exception_info
+
+    def __exit__(
+        self,
+        __exc_type: Optional[Type[BaseException]],
+        __exc_value: Optional[BaseException],
+        __traceback: Optional[TracebackType],
+    ) -> bool:
+        result = self._catcher.__exit__(__exc_type, __exc_value, __traceback)
+        if self._exception_info is not None:
+            self._check_attributes(self._exception_info.value)
+        return result