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Hard crash when deleting from Dictionary #2530
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Thank you for the reproducible example, I will look into it. If you want to have a go at it, you are more than welcome though.
Side note: I have checked that this is not a regression in today's release, the same error happens on all 3.* versions.
My first guess is that we simply don't implement the deletion case. For __delitem__, Python passes a null to the value parameter of mp_ass_subscript.
mp_ass_subscript is implemented via Indexers which does not have an equivalent to __delitem__.
So, we have the following options:
- Throw an exception (that can be caught), I think this is a good first step
- For ICollection, IDictionary, IList, and classes that implement these, special-case scalar deletions to use the respective remove functions
Hm, this actually should work due to
Maybe it is not enabled by default? It might not be enabled due to scenarios where you don't want these methods to appear in any kind of reflection (from Python).
And it would work, except that the Dictionary class provides its own implementation of __delitem__ that overrides the one in MutableMappingMixin:
>>> import pythonnet; pythonnet.load('coreclr'); import clr >>> import System >>> DictType = System.Collections.Generic.Dictionary[System.String, System.Int32] >>> d = DictType() >>> d['a'] = 1 >>> d['b'] = 2 >>> d['c'] = 3 >>> for cls in DictType.mro(): # print the classes that implement __delitem__ ... if hasattr(cls, '__delitem__'): ... print('@@@', cls) @@@ <class 'System.Collections.Generic.Dictionary[String,Int32]'> @@@ <class 'clr._extras.collections.MutableMappingMixin'> @@@ <class 'collections.abc.MutableMapping'> >>> MutableMappingMixin = DictType.mro()[2] >>> MutableMappingMixin <class 'clr._extras.collections.MutableMappingMixin'> >>> dict(d) {'a': 1, 'b': 2, 'c': 3} >>> MutableMappingMixin.__delitem__(d, 'c') # Calling directly using base class, works OK >>> dict(d) {'a': 1, 'b': 2} >>> super(DictType, d).__delitem__('b') # Calling on superclass also works OK >>> dict(d) {'a': 1} >>> DictType.__delitem__(d, 'a') # Equivalent to d.__delitem('a') and del d['a'], crashes Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object. at Python.Runtime.BorrowedReference.DangerousGetAddress() in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Native/BorrowedReference.cs:line 18 at Python.Runtime.NewReference..ctor(BorrowedReference reference, Boolean canBeNull) in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Native/NewReference.cs:line 20 at Python.Runtime.Runtime.PyTuple_SetItem(BorrowedReference pointer, IntPtr index, BorrowedReference value) in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Runtime.cs:line 1482 at Python.Runtime.ClassBase.mp_ass_subscript_impl(BorrowedReference ob, BorrowedReference idx, BorrowedReference v) in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Types/ClassBase.cs:line 498
Well, the direct implementation always wins, and Python, counts mp_ass_subscript as an implementation for __setitem__ and __delitem__. We could go through the __mro__ to find the mixin, but at that point it might make more sense to just extend the mp_ass_subscript implementation to handle the deletion itself.
Reacted by Diego Baldassar- added 2 commits that reference this issue on Apr 11, 2025
- added a commit that references this issue on Apr 11, 2025
Environment
Details
Remove an element from a .NET Dictionary using the del operator (__delitem__).
If you can provide a Minimal, Complete, and Verifiable example this will help us understand the issue.
I reduced the problem to the following example, simply run from the command line:
The program crashed with the following output:
Runtime: CoreCLR ============= Version: <undefined> Initialized: True Shut down: False Properties: HOST_RUNTIME_CONTRACT = 0x600003a840c8 PROBING_DIRECTORIES = RUNTIME_IDENTIFIER = osx-arm64 FX_DEPS_FILE = /usr/local/share/dotnet/shared/Microsoft.NETCore.App… APP_CONTEXT_DEPS_FILES = /usr/local/share/dotnet/shared/Microsoft.N… APP_CONTEXT_BASE_DIRECTORY = PLATFORM_RESOURCE_ROOTS = : NATIVE_DLL_SEARCH_DIRECTORIES = :/usr/local/share/dotnet/shared/Mic… TRUSTED_PLATFORM_ASSEMBLIES = /usr/local/share/dotnet/shared/Micros… __delitem__ is implemented by <class 'System.Collections.Generic.Dictionary[Int32,String]'> Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object. at Python.Runtime.BorrowedReference.DangerousGetAddress() in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Native/BorrowedReference.cs:line 18 at Python.Runtime.NewReference..ctor(BorrowedReference reference, Boolean canBeNull) in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Native/NewReference.cs:line 20 at Python.Runtime.Runtime.PyTuple_SetItem(BorrowedReference pointer, IntPtr index, BorrowedReference value) in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Runtime.cs:line 1482 at Python.Runtime.ClassBase.mp_ass_subscript_impl(BorrowedReference ob, BorrowedReference idx, BorrowedReference v) in /home/benedikt/.cache/uv/sdists-v6/.tmpkW03e6/pythonnet-3.0.5/src/runtime/Types/ClassBase.cs:line 498 [1] 56976 abort python3.12 /tmp/ramdisk/delme_test_pythonnet.pyNotice that __delitem__ is also implemented by the MutableMappingMixin class here, which simply calls the Remove() method, but Dictionary has its own implementation (that I can't find), which takes precedence.
The former would have worked correctly (tested), as Remove() works as usual.