QUERY · ISSUE

`tuple + class MyTuple(tuple)` performs a wrong type cast

openby dimpoloopened 2021-05-24updated 2026-03-24

py-core

class MyTuple(tuple):
    pass

print((1,2) + MyTuple((3,4)))  # prints (1, 2, (nil))

Relevant code:
https://github.com/micropython/micropython/blob/3b950ed2959c603ff30dd6052c157e7981c4d2d6/py/objtuple.c#L145-L153
mp_obj_tuple_binary_op checks rhs with mp_obj_is_subclass_fast and then casts it to mp_obj_tuple_t

CANDIDATE · PULL REQUEST

py: Simplify tuple subclass equality testing

mergedby dpgeorgeopened 2020-02-18updated 2020-02-19

py-core

This removes code that handles tuple-subclass equality test.

Since commit 3aab54bf434e7f025a91ea05052f1bac439fad8c this piece of code is no longer needed because the top-level function mp_obj_equal_not_equal() now handles the case of user types, and will never call tuple's binary_op function with MP_BINARY_OP_EQUAL and a non-tuple on the RHS.

Tests are added for additional coverage of related parts of this function.

@nickovs FYI, looks to be another little win for the improved equality testing.

Assessment

Q Qwen · high

Both touch py/objtuple.c and involve tuple subclass handling in binary operations, but they address distinct operations. The query reports a bug in the concatenation path (mp_obj_tuple_binary_op casting rhs to mp_obj_tuple_t incorrectly after an is_subclass check). PR #5661 removes now-redundant code from the equality/comparison path (tuple_cmp_helper), which was cleaned up because mp_obj_equal_not_equal() already handles user types upstream. The PR does not touch the concatenation code path and does not fix the reported bug.

Suggested action

Leave the query issue open. Reference PR #5661 as prior art for tuple subclass handling cleanup, but a separate fix is needed in mp_obj_tuple_binary_op to correctly handle the RHS when it is a tuple subclass during concatenation (e.g., by extracting the underlying tuple items rather than casting directly to mp_obj_tuple_t).

`tuple + class MyTuple(tuple)` performs a wrong type cast

py: Simplify tuple subclass equality testing

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