fix: handling of Literal datatype (#2076)

Check datatype against `None` instead of checking it's truthiness (i.e. `if datatype is not None:` instead of `if datatype:`). Checking truthiness instead of `is not None` causes a blank string to be treated the same as None. The consequence of this was that `Literal.datatype` could be a `str`, a `URIRef` or `None`, instead of just a `URIRef` or `None` as was seemingly intended. Other changes: - Changed the type of `Literal.datatype` to be `Optional[URIRef]` instead of `Optional[str]` now that `str` will always be converted to `URIRef` even if it is a blank string. - Changed `rdflib.util._coalesce` to make it easier and safer to use with a non-`None` default value. - Changed `rdflib.util` to avoid issues with circular imports.
RDFLib · Aug 12, 2022 · a39d143 · a39d143
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diff --git a/.gitignore b/.gitignore
@@ -2,6 +2,7 @@ RDFLib.sublime-project
 /docs/_build/
 RDFLib.sublime-workspace
 coverage/
+cov.xml
 /.hgtags
 /.hgignore
 build/

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -248,6 +248,25 @@ and will be removed for release.
 <!-- -->
 <!-- -->
 
+
+<!-- -->
+<!-- -->
+<!-- CHANGE BARRIER: START PR #2076 -->
+<!-- -->
+<!-- -->
+
+- Fixed handling of `Literal` `datatype` to correctly differentiate between
+  blank string values and undefined values, also changed the datatype of
+  `rdflib.term.Literal.datatype` from `Optional[str]` to `Optional[URIRef]` now
+  that all non-`URIRef` `str` values will be converted to `URIRef`.
+  [PR #2076](https://github.com/RDFLib/rdflib/pull/2076).
+
+<!-- -->
+<!-- -->
+<!-- CHANGE BARRIER: END PR #2076 -->
+<!-- -->
+<!-- -->
+
 <!-- -->
 <!-- -->
 <!-- CHANGE BARRIER: START -->

diff --git a/Taskfile.yml b/Taskfile.yml
@@ -148,7 +148,7 @@ tasks:
   mypy:
     desc: Run mypy
     cmds:
-      - "{{._PYTHON | shellQuote}} -m mypy --show-error-context --show-error-codes"
+      - "{{._PYTHON | shellQuote}} -m mypy --show-error-context --show-error-codes {{.CLI_ARGS}}"
 
   lint:fix:
     desc: Fix auto-fixable linting errors

diff --git a/rdflib/plugins/stores/memory.py b/rdflib/plugins/stores/memory.py
@@ -217,14 +217,12 @@ def bind(self, prefix: str, namespace: "URIRef", override: bool = True) -> None:
             self.__namespace[prefix] = namespace
         else:
             # type error: Invalid index type "Optional[URIRef]" for "Dict[URIRef, str]"; expected type "URIRef"
-            # type error: Incompatible types in assignment (expression has type "Optional[str]", target has type "str")
-            self.__prefix[_coalesce(bound_namespace, namespace)] = _coalesce(  # type: ignore[index, assignment]
-                bound_prefix, prefix
+            self.__prefix[_coalesce(bound_namespace, namespace)] = _coalesce(  # type: ignore[index]
+                bound_prefix, default=prefix
             )
             # type error: Invalid index type "Optional[str]" for "Dict[str, URIRef]"; expected type "str"
-            # type error: Incompatible types in assignment (expression has type "Optional[URIRef]", target has type "URIRef")
-            self.__namespace[_coalesce(bound_prefix, prefix)] = _coalesce(  # type: ignore[index, assignment]
-                bound_namespace, namespace
+            self.__namespace[_coalesce(bound_prefix, prefix)] = _coalesce(  # type: ignore[index]
+                bound_namespace, default=namespace
             )
 
     def namespace(self, prefix: str) -> Optional["URIRef"]:
@@ -538,14 +536,13 @@ def bind(self, prefix: str, namespace: "URIRef", override: bool = True) -> None:
             self.__namespace[prefix] = namespace
         else:
             # type error: Invalid index type "Optional[URIRef]" for "Dict[URIRef, str]"; expected type "URIRef"
-            # type error: Incompatible types in assignment (expression has type "Optional[str]", target has type "str")
-            self.__prefix[_coalesce(bound_namespace, namespace)] = _coalesce(  # type: ignore[index, assignment]
-                bound_prefix, prefix
+            self.__prefix[_coalesce(bound_namespace, namespace)] = _coalesce(  # type: ignore[index]
+                bound_prefix, default=prefix
             )
             # type error: Invalid index type "Optional[str]" for "Dict[str, URIRef]"; expected type "str"
             # type error: Incompatible types in assignment (expression has type "Optional[URIRef]", target has type "URIRef")
-            self.__namespace[_coalesce(bound_prefix, prefix)] = _coalesce(  # type: ignore[index, assignment]
-                bound_namespace, namespace
+            self.__namespace[_coalesce(bound_prefix, prefix)] = _coalesce(  # type: ignore[index]
+                bound_namespace, default=namespace
             )
 
     def namespace(self, prefix: str) -> Optional["URIRef"]:

diff --git a/rdflib/term.py b/rdflib/term.py
@@ -69,6 +69,7 @@
 )
 
 import rdflib
+import rdflib.util
 from rdflib.compat import long_type
 
 if TYPE_CHECKING:
@@ -598,7 +599,7 @@ class Literal(Identifier):
     _value: Any
     _language: Optional[str]
     # NOTE: _datatype should maybe be of type URIRef, and not optional.
-    _datatype: Optional[str]
+    _datatype: Optional[URIRef]
     _ill_typed: Optional[bool]
     __slots__ = ("_language", "_datatype", "_value", "_ill_typed")
 
@@ -624,7 +625,7 @@ def __new__(
         if lang is not None and not _is_valid_langtag(lang):
             raise ValueError(f"'{str(lang)}' is not a valid language tag!")
 
-        if datatype:
+        if datatype is not None:
             datatype = URIRef(datatype)
 
         value = None
@@ -633,7 +634,7 @@ def __new__(
             # create from another Literal instance
 
             lang = lang or lexical_or_value.language
-            if datatype:
+            if datatype is not None:
                 # override datatype
                 value = _castLexicalToPython(lexical_or_value, datatype)
             else:
@@ -644,7 +645,7 @@ def __new__(
             # passed a string
             # try parsing lexical form of datatyped literal
             value = _castLexicalToPython(lexical_or_value, datatype)
-            if datatype and datatype in _toPythonMapping:
+            if datatype is not None and datatype in _toPythonMapping:
                 # datatype is a recognized datatype IRI:
                 # https://www.w3.org/TR/rdf11-concepts/#dfn-recognized-datatype-iris
                 dt_uri: URIRef = URIRef(datatype)
@@ -661,10 +662,12 @@ def __new__(
             value = lexical_or_value
             _value, _datatype = _castPythonToLiteral(lexical_or_value, datatype)
 
-            datatype = datatype or _datatype
+            _datatype = None if _datatype is None else URIRef(_datatype)
+
+            datatype = rdflib.util._coalesce(datatype, _datatype)
             if _value is not None:
                 lexical_or_value = _value
-            if datatype:
+            if datatype is not None:
                 lang = None
 
         if isinstance(lexical_or_value, bytes):
@@ -729,7 +732,7 @@ def language(self) -> Optional[str]:
         return self._language
 
     @property
-    def datatype(self) -> Optional[str]:
+    def datatype(self) -> Optional[URIRef]:
         return self._datatype
 
     def __reduce__(
@@ -743,7 +746,7 @@ def __reduce__(
     def __getstate__(self) -> Tuple[None, Dict[str, Union[str, None]]]:
         return (None, dict(language=self.language, datatype=self.datatype))
 
-    def __setstate__(self, arg: Tuple[Any, Dict[str, str]]) -> None:
+    def __setstate__(self, arg: Tuple[Any, Dict[str, Any]]) -> None:
         _, d = arg
         self._language = d["language"]
         self._datatype = d["datatype"]
@@ -1096,8 +1099,8 @@ def __gt__(self, other: Any) -> bool:
 
             # plain-literals and xsd:string literals
             # are "the same"
-            dtself = self.datatype or _XSD_STRING
-            dtother = other.datatype or _XSD_STRING
+            dtself = rdflib.util._coalesce(self.datatype, default=_XSD_STRING)
+            dtother = rdflib.util._coalesce(other.datatype, default=_XSD_STRING)
 
             if dtself != dtother:
                 if rdflib.DAWG_LITERAL_COLLATION:
@@ -1129,9 +1132,9 @@ def __gt__(self, other: Any) -> bool:
             # same language, same lexical form, check real dt
             # plain-literals come before xsd:string!
             if self.datatype != other.datatype:
-                if not self.datatype:
+                if self.datatype is None:
                     return False
-                elif not other.datatype:
+                elif other.datatype is None:
                     return True
                 else:
                     return self.datatype > other.datatype
@@ -1186,7 +1189,7 @@ def _comparable_to(self, other: Any) -> bool:
         rich-compare with this literal
         """
         if isinstance(other, Literal):
-            if self.datatype and other.datatype:
+            if self.datatype is not None and other.datatype is not None:
                 # two datatyped literals
                 if (
                     self.datatype not in XSDToPython
@@ -1247,7 +1250,7 @@ def __hash__(self) -> int:  # type: ignore[override]
         # Directly accessing the member is faster than the property.
         if self._language:
             res ^= hash(self._language.lower())
-        if self._datatype:
+        if self._datatype is not None:
             res ^= hash(self._datatype)
         return res
 
@@ -1342,8 +1345,8 @@ def eq(self, other: Any) -> bool:
             if (self.language or "").lower() != (other.language or "").lower():
                 return False
 
-            dtself = self.datatype or _XSD_STRING
-            dtother = other.datatype or _XSD_STRING
+            dtself = rdflib.util._coalesce(self.datatype, default=_XSD_STRING)
+            dtother = rdflib.util._coalesce(other.datatype, default=_XSD_STRING)
 
             if dtself == _XSD_STRING and dtother == _XSD_STRING:
                 # string/plain literals, compare on lexical form
@@ -1556,7 +1559,7 @@ def _literal_n3(
 
         datatype = self.datatype
         quoted_dt = None
-        if datatype:
+        if datatype is not None:
             if qname_callback:
                 quoted_dt = qname_callback(datatype)
             if not quoted_dt:
@@ -1906,16 +1909,18 @@ def _well_formed_negative_integer(lexical: Union[str, bytes], value: Any) -> boo
     URIRef(_XSD_PFX + "token"),
 )
 
+_StrT = TypeVar("_StrT", bound=str)
+
 
 def _py2literal(
     obj: Any,
     pType: Any,  # noqa: N803
     castFunc: Optional[Callable[[Any], Any]],
-    dType: Optional[str],
-) -> Tuple[Any, Optional[str]]:
-    if castFunc:
+    dType: Optional[_StrT],
+) -> Tuple[Any, Optional[_StrT]]:
+    if castFunc is not None:
         return castFunc(obj), dType
-    elif dType:
+    elif dType is not None:
         return obj, dType
     else:
         return obj, None
@@ -2062,7 +2067,7 @@ def _reset_bindings() -> None:
 
 
 def _castLexicalToPython(  # noqa: N802
-    lexical: Union[str, bytes], datatype: Optional[str]
+    lexical: Union[str, bytes], datatype: Optional[URIRef]
 ) -> Any:
     """
     Map a lexical form to the value-space for the given datatype