I'm writing a Python script that needs to write some data to a temporary file, then create a subprocess running a C++ program that will read the temporary file. I'm trying to use NamedTemporaryFile for this, but according to the docs,

Whether the name can be used to open the file a second time, while the named temporary file is still open, varies across platforms (it can be so used on Unix; it cannot on Windows NT or later).

And indeed, on Windows if I flush the temporary file after writing, but don't close it until I want it to go away, the subprocess isn't able to open it for reading.

I'm working around this by creating the file with delete=False, closing it before spawning the subprocess, and then manually deleting it once I'm done:

fileTemp = tempfile.NamedTemporaryFile(delete = False)
try:
    fileTemp.write(someStuff)
    fileTemp.close()
    # ...run the subprocess and wait for it to complete...
finally:
    os.remove(fileTemp.name)

This seems inelegant. Is there a better way to do this? Perhaps a way to open up the permissions on the temporary file so the subprocess can get at it?

At least if you open a temporary file using existing Python libraries, accessing it from multiple processes is not possible in case of Windows. According to MSDN you can specify a 3rd parameter (dwSharedMode) shared mode flag FILE_SHARE_READ to CreateFile() function which:

Enables subsequent open operations on a file or device to request read access. Otherwise, other processes cannot open the file or device if they request read access. If this flag is not specified, but the file or device has been opened for read access, the function fails.

So, you can write a Windows specific C routine to create a custom temporary file opener function, call it from Python and then you can make your sub-process access the file without any error. But I think you should stick with your existing approach as it is the most portable version and will work on any system and thus is the most elegant implementation.

• Discussion on Linux and windows file locking can be found here.

EDIT: Turns out it is possible to open & read the temporary file from multiple processes in Windows too. See Piotr Dobrogost's answer.