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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Copying bytes object to shared memory list truncates trailing zeros","articleBody":"# Bug report\r\n\r\n**tl;dr; See [stack overflow post](https://stackoverflow.com/questions/76734284/copying-bytes-object-to-shared-memory-list-truncates-trailing-zeros)**\r\n\r\nWhen copying a `bytes` object to a shareable list, the trailing zeros are stripped causing data loss. This doesn't appear in the documentation as far as I can tell, and seems to be unexpected behavior related to the implementation.\r\n\r\nExample code:\r\n```python\r\nfrom multiprocessing import shared_memory as shm\r\n\r\nshmList = shm.ShareableList([bytes(50)])\r\ntestBytes = bytes.fromhex(\"00112233445566778899aabbccddeeff0000\")\r\n\r\nshmList[0] = testBytes\r\nprint(testBytes)\r\nprint(shmList[0])\r\n\r\nshmList.shm.close()\r\nshmList.shm.unlink()\r\n```\r\n\r\nOutput:\r\n```\r\nb'\\x00\\x11\"3DUfw\\x88\\x99\\xaa\\xbb\\xcc\\xdd\\xee\\xff\\x00\\x00'\r\nb'\\x00\\x11\"3DUfw\\x88\\x99\\xaa\\xbb\\xcc\\xdd\\xee\\xff'\r\n```\r\n\r\nOffending portion of CPython [code](https://github.com/python/cpython/blob/d81b4f8ff84311fa737e62f2883442ec06d7d5d8/Lib/multiprocessing/shared_memory.py#L280):\r\n```python\r\n_back_transforms_mapping = {\r\n        0: lambda value: value,                   # int, float, bool\r\n        1: lambda value: value.rstrip(b'\\x00').decode(_encoding),  # str\r\n        2: lambda value: value.rstrip(b'\\x00'),   # bytes\r\n        3: lambda _value: None,                   # None\r\n    }\r\n```\r\n\r\n\r\n\u003c!-- gh-linked-prs --\u003e\r\n### Linked PRs\r\n* gh-107266\r\n* gh-107269\r\n* gh-107270\r\n\u003c!-- /gh-linked-prs --\u003e\r\n","author":{"url":"https://github.com/pinkhamr-fb","@type":"Person","name":"pinkhamr-fb"},"datePublished":"2023-07-21T00:12:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/106939/cpython/issues/106939"}