refactor: create a private module-level constant for bom_link_prefix

Signed-off-by: Saquib Saifee <[email protected]>

Author: Saquib Saifee

cyclonedx/model/__init__.py

@@ -55,6 +55,8 @@
 )
 from .bom_ref import BomRef
 
+_BOM_LINK_PREFIX = 'urn:cdx:'
+
 
 @serializable.serializable_enum
 class DataFlow(str, Enum):
@@ -789,7 +791,7 @@ def make_bom_link(
             XsUri: Instance of XsUri with the generated BOM-Link URI.
         """
         bom_ref_part = f'#{url_quote(str(bom_ref))}' if bom_ref else ''
-        return cls(f'urn:cdx:{serial_number}/{version}{bom_ref_part}')
+        return cls(f'{_BOM_LINK_PREFIX}{serial_number}/{version}{bom_ref_part}')
 
     def is_bom_link(self) -> bool:
         """
@@ -798,7 +800,7 @@ def is_bom_link(self) -> bool:
         Returns:
             `bool`
         """
-        return self._uri.startswith('urn:cdx:')
+        return self._uri.startswith(_BOM_LINK_PREFIX)
 
 
 @serializable.serializable_class

cyclonedx/model/bom.py

@@ -37,7 +37,7 @@
     SchemaVersion1Dot6,
 )
 from ..serialization import LicenseRepositoryHelper, UrnUuidHelper
-from . import ExternalReference, Property
+from . import _BOM_LINK_PREFIX, ExternalReference, Property
 from .bom_ref import BomRef
 from .component import Component
 from .contact import OrganizationalContact, OrganizationalEntity
@@ -663,7 +663,7 @@ def register_dependency(self, target: Dependable, depends_on: Optional[Iterable[
                 self.register_dependency(target=_d2, depends_on=None)
 
     def urn(self) -> str:
-        return f'urn:cdx:{self.serial_number}/{self.version}'
+        return f'{_BOM_LINK_PREFIX}{self.serial_number}/{self.version}'
 
     def validate(self) -> bool:
         """