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gh-115754: Use Py_GetConstant(Py_CONSTANT_EMPTY_BYTES) by vstinner · Pull Request #125581 · python/cpython · GitHub

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gh-115754: Use Py_GetConstant(Py_CONSTANT_EMPTY_BYTES) - #125581

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gh-115754: Use Py_GetConstant(Py_CONSTANT_EMPTY_BYTES)#125581
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vstinner commented Oct 16, 2024 •
edited by bedevere-app Bot
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Replace PyBytes_FromStringAndSize(NULL, 0)
with Py_GetConstant(Py_CONSTANT_EMPTY_BYTES).

pythongh-115754: Use Py_GetConstant(Py_CONSTANT_EMPTY_BYTES)
e65dcc8 
Replace PyBytes_FromStringAndSize(NULL, 0)
with Py_GetConstant(Py_CONSTANT_EMPTY_BYTES).
bedevere-app Bot mentioned this pull request Oct 16, 2024
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serhiy-storchaka reviewed Oct 16, 2024
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Please wait.

serhiy-storchaka reviewed Oct 16, 2024
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I am not comfortable with this change.

  1. There is nothing wrong in using PyBytes_FromStringAndSize(NULL, 0). It works, it worked, and it will always work. This is not inefficient or private API.
  2. PyBytes_FromStringAndSize() returns a new reference, while Py_GetConstant() returns a borrowed reference. Even if an empty bytes object is immutable, there is a value of always using balanced incref/decref. It makes the intention clearer and the code more error-proof. When there are several exit points and some return a new reference and other return borrowed reference, you can immediately say that there is a bug. If it is not a bug, you will waste time and mental efforts in vain on analyzing the code.
  3. This creates a tiny obstacle for future backportings.

In summary, this is a cosmetic change which makes the code more difficult to maintain without significant gain.

vstinner commented Oct 16, 2024

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PyBytes_FromStringAndSize() returns a new reference, while Py_GetConstant() returns a borrowed reference.

Py_GetConstant() returns a new reference: https://docs.python.org/dev/c-api/object.html#c.Py_GetConstant

serhiy-storchaka commented Oct 16, 2024

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Oh, nice. That eliminates most of my objections. There is still an issue with reasoning such change. This look like change for the sake of change.

vstinner commented Oct 25, 2024

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I would like to get rid of PyBytes_FromStringAndSize(NULL, size) calls which create an incomplete bytes object, but PyBytes_FromStringAndSize(NULL, 0) doesn't have this issue.

Py_GetConstant(Py_CONSTANT_EMPTY_BYTES) is simpler and a little bit faster than PyBytes_FromStringAndSize(NULL, 0).

In general, I would prefer to make Py_GetConstant(Py_CONSTANT_EMPTY_BYTES) the reference function to get an empty byte string.

vstinner commented Oct 25, 2024

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See also https://discuss.python.org/t/what-do-you-think-of-deprecating-c-apis-to-modify-immutable-strings/67057

vstinner commented Nov 6, 2024

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I failed to convince @serhiy-storchaka, so I just close my PR.

vstinner closed this Nov 6, 2024
vstinner deleted the empty_bytes2 branch November 6, 2024 15:26
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