Comparing two codes where one is erroneously set as a SRT will throw KeyError

[erikogabrielsson]

Describe the bug
The comparision of two codes does mapping from SRT codes to SCT. If comparision is done on a code that has SRT as the scheme designator but is not in the dictionary of SRT to SCT mappings, the comparision will throw a KeyError.

Expected behavior
If the mapping from SRT to SCT is not possible I would excpect the comparision to return False if the codes are not equal.

Steps To Reproduce

wrong_srt_code = Code("111729", "SRT", "Specimen storage") # Is actually a DCM code
sct_code = Code("127790008", "SCT", "Staining")

wrong_srt_code == sct_code

Throws:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[9], [line 4](vscode-notebook-cell:?execution_count=9&line=4)
      [1](vscode-notebook-cell:?execution_count=9&line=1) wrong_srt_code = Code("111729", "SRT", "Specimen storage") # Is actually a DCM code
      [2](vscode-notebook-cell:?execution_count=9&line=2) sct_code = Code("127790008", "SCT", "Staining")
----> [4](vscode-notebook-cell:?execution_count=9&line=4) wrong_srt_code == sct_code

File [c:\work\notebooks\.venv311\Lib\site-packages\pydicom\sr\coding.py:26](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:26), in Code.__eq__(self, other)
     [23](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:23) def __eq__(self, other: Any) -> Any:
     [24](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:24)     if self.scheme_designator == "SRT":
     [25](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:25)         self_mapped = Code(
---> [26](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:26)             value=snomed_mapping["SRT"][self.value],
     [27](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:27)             meaning="",
     [28](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:28)             scheme_designator="SCT",
     [29](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:29)             scheme_version=self.scheme_version,
     [30](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:30)         )
     [31](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:31)     else:
     [32](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:32)         self_mapped = Code(
     [33](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:33)             value=self.value,
     [34](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:34)             meaning="",
     [35](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:35)             scheme_designator=self.scheme_designator,
     [36](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:36)             scheme_version=self.scheme_version,
     [37](file:///C:/work/notebooks/.venv311/Lib/site-packages/pydicom/sr/coding.py:37)         )

KeyError: '111729'

Your environment
Please use the pydicom.env_info module (available in pydicom 2 or later)
to gather information about your environment and paste it into the issue:

module       | version
------       | -------
platform     | Windows-10-10.0.22631-SP0
Python       | 3.11.6 (tags/v3.11.6:8b6ee5b, Oct  2 2023, 14:57:12) [MSC v.1935 64 bit (AMD64)]
pydicom      | 3.0.0.dev0
gdcm         | 3.0.22
jpeg_ls      | **cannot determine version**
numpy        | 1.26.2
PIL          | 10.1.0
pylibjpeg    | 1.4.0
openjpeg     | 1.3.2
libjpeg      | _module not found_