why doesn't an mmap.mmap object have some kind of memoryview method?

[Cameron Simpson]

I should add that I'm using CPython 3 on a Mac, happy to receive CPython 3 
UNIX-specific advice. - Cameron

On 06Aug2018 09:28, Cameron Simpson <cs at cskk.id.au> wrote:
>I'm tinkering with a module which scans video files. The MP4 parser 
>has a `discard_data` parameter which tells certain parts of the parser 
>to discard some of the scanned data, particularly the MDAT box parse 
>because I don't normally want to blow the machine's RAM on a huge 
>video stream - I'm normally parsing out the semantic info such as 
>metadata.
>
>However, I would _like_ to keep it available in a frugal fashion if I 
>can, and it seems to me that the mmap module is ideal: map the file 
>into memory, use the file itself as the backing store, and return 
>views of the mmap.
>
>But slicing a mmap object returns a bytes, which I _imagine_ to be a 
>copy of the file data instead of a view into the mapping (because 
>bytes are supposed to be immutable, and in theory some other actor 
>might change the file even though I myself have it mapped read only).
>
>It seems obvious to me that a method returning a memoryview of the 
>mapped file would be very handy here: no data copies at all, and not 
>even any I/O unless the data are accessed. But I see no such method in 
>the documentation.
>
>Does anyone have any insight here?
>
>Cheers,
>Cameron Simpson <cs at cskk.id.au>