[ctypes] [feature request] Create a Python string without buffer copies given a bytes pointer, size, kind

[vadimkantorov]

In interop scenarios, it might be useful to be able to have a Python string referencing an existing buffer without copies (e.g. if the underlying char data is stored in NumPy/PyTorch tensors, accessing these char buffers with a standard Python interface is helpful for debugging and sometimes for perf).

I think it currently might be possible with ctypes and making use of existing PyUnicode/PyASCIIobject object layout and resetting the size/data fields to my own values.

I agree that usefulness over copying the byte buffer is not very prominent, but still might be useful in some specific scenarios: e.g. by mmap'ing a giant string from a disk file and being able to examine it in an easy way

[sunmy2019]

CPython string does not need to be copied since they are immutable.

mmap'ing a giant string

Use mmap.mmap

making use of existing PyUnicode/PyASCIIobject object

A lot of code needs to be changed. Cost > Benefits.

[sunmy2019]

You can always use Python buffer protocol in your use cases.

[vadimkantorov]

I agree that the usecase is narrow, but if the hack I'm thinking of:

1. construct an empty or 1-character-long string with the user-provided kind
2. replace size and data fields with user-provided values

is possible, then this function can be relatively simple to implement in ctypes module without any redesign of string data structures, and useful in some debugging/zero-copy interop scenarios (e.g. if the underlying char data is stored in NumPy/PyTorch tensors)