rhyslloyd1 via python-win32 wrote:
I am trying to open a memory mapped file using Python. I originally used the "mmap" module from Python however I had issues with it because I had to use a fixed size for the file even though my goal was to open an existing file of which the size would be unknown.
The file size isn't really "unknown". It's just not known in advance. There are many ways to find the size of a file. Plus, the "mmap" module accepts 0 as a size parameter, meaning "map the whole file".
I am now using the "mmapfile.mmapfile" function. My code looks like this <https://pastebin.com/QygT2wp6>. In the docs <http://timgolden.me.uk/pywin32-docs/mmapfile__mmapfile_meth.html> it says I can use a file name of "None" if I'm planning on opening an existing file. This <https://pastebin.com/2FVhpDiB> is the error I get when running my code.
There are a couple of misunderstanding here. It is important to realize that the name of the mapping object is quite different from the name of the file being mapped. The Windows memory-mapping concept is quite general, and is often used as a way to share memory between multiple processes. In that case, you just want a chunk of memory without bothering with a file on disk. In that case, you'd create a mapping object with a name, but no file name.
If you're just mapping an existing file, you need to supply the file name, but you don't need to supply a name for the mapping object. The code you showed creates a shared memory object that does not map a file on disk. The shared memory object has a name (the GUID), and another application could open that named object, but it doesn't map to a file.
If you want to open a mapping to an existing file, specify the name of the file as File= and specify Name=None.
However, you can do all of this with the mmap module as well. If you have a file called "data.bin", you can do
import mmap
fn = open('data.bin','rb')
data = mmap.mmap( fn.fileno(), 0, access=mmap.ACCESS_READ )
That maps the whole file, and len(data) will tell you how large it is.
--
Tim Roberts, t...@probo.com
Providenza & Boekelheide, Inc.
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