On 2018-08-06 00:28, Cameron Simpson 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?
The docs show that although slicing a mmap returns bytes, you can assign
to a slice of a mmap itself.
You can also give an offset and length into the file when you create the
mmap.
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