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

Cameron Simpson cs at cskk.id.au
Sun Aug 5 19:28:13 EDT 2018 
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>
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