add BaseAttrib.discard_mtext() method

docs/source/blocks/attdef.rst

@@ -60,4 +60,6 @@ Inherited DXF attributes :ref:`Common graphical DXF attributes`
 
     .. automethod:: embed_mtext
 
+    .. automethod:: discard_mtext
+
 .. _DXF Reference: http://help.autodesk.com/view/OARX/2018/ENU/?guid=GUID-F0EA099B-6F88-4BCC-BEC7-247BA64838A4

docs/source/blocks/attrib.rst

@@ -54,5 +54,6 @@ Inherited DXF attributes :ref:`Common graphical DXF attributes`
 
     .. automethod:: embed_mtext
 
+    .. automethod:: discard_mtext
 
 .. _DXF Reference: http://help.autodesk.com/view/OARX/2018/ENU/?guid=GUID-7DD8B495-C3F8-48CD-A766-14F9D7D0DD9B

src/ezdxf/entities/attrib.py

@@ -366,7 +366,7 @@ def set_mtext(self, mtext: MText, graphic_properties=True) -> None:
 
     def embed_mtext(self, mtext: MText, graphic_properties=True) -> None:
         """Set multi-line properties from a :class:`MText` entity and destroy the
-        source entity afterwards.
+        source entity afterward.
 
         The multi-line ATTRIB/ATTDEF entity requires DXF R2018, otherwise an
         ordinary single line ATTRIB/ATTDEF entity will be exported.
@@ -380,6 +380,15 @@ def embed_mtext(self, mtext: MText, graphic_properties=True) -> None:
         self.set_mtext(mtext, graphic_properties)
         mtext.destroy()
 
+    def discard_mtext(self) -> None:
+        """Discard multi-line feature.
+
+        The embedded MTEXT will be removed and the ATTRIB/ATTDEF will be converted to a
+        single-line attribute.
+        """
+        self._embedded_mtext = None
+        self.dxf.attribute_type = const.ATTRIB_TYPE_SINGLE_LINE
+
     def register_resources(self, registry: xref.Registry) -> None:
         """Register required resources to the resource registry."""
         super().register_resources(registry)

tests/test_02_dxf_graphics/test_208_attrib.py

@@ -6,7 +6,7 @@
 import ezdxf
 from ezdxf.entities import Attrib, MText
 from ezdxf.entities.attrib import EmbeddedMText, EmbeddedMTextNS
-from ezdxf.lldxf.const import DXF12, DXF2000
+from ezdxf.lldxf import const
 from ezdxf.lldxf.tagwriter import TagCollector, basic_tags_from_text
 from ezdxf.math import Matrix44
 from ezdxf.audit import Auditor
@@ -159,7 +159,9 @@ def test_load_from_text(entity):
     assert entity.dxf.insert == (0, 0, 0)
 
 
-@pytest.mark.parametrize("txt,ver", [(ENTITY_R2000, DXF2000), (ENTITY_R12, DXF12)])
+@pytest.mark.parametrize(
+    "txt,ver", [(ENTITY_R2000, const.DXF2000), (ENTITY_R12, const.DXF12)]
+)
 def test_write_dxf(txt, ver):
     expected = basic_tags_from_text(txt)
     attdef = TEST_CLASS.from_text(txt)
@@ -237,6 +239,11 @@ def test_set_mtext(self):
         attrib.set_mtext(mtext)
         assert attrib.has_embedded_mtext_entity is True
 
+    def test_discard_mtext(self, attrib):
+        attrib.discard_mtext()
+        assert attrib.has_embedded_mtext_entity is False
+        assert attrib.dxf.attribute_type == const.ATTRIB_TYPE_SINGLE_LINE
+
     def test_transformation_of_embedded_mtext(self):
         attrib = Attrib.new(dxfattribs={"color": 3, "text": "TEST"})
         mtext = MText.new(dxfattribs={"color": 3})