Python in a Nutshell

Name

mmap

Synopsis

mmap(filedesc,length,tagname='')    # Windows
mmap(filedesc,length,flags=MAP_SHARED,
     prot=PROT_READ|PROT_WRITE)     # Unix

Creates and returns an mmap object m that maps into memory the first length bytes of the file indicated by file descriptor filedesc. filedesc must normally be a file descriptor opened for both reading and writing (except, on Unix-like platforms, when argument prot requests only reading or only writing). File descriptors are covered in Section 10.2.8. To get an mmap object m that refers to a Python file object f, use m =mmap.mmap( f .fileno( ),length ).

On Windows only, you can pass a string tagname to give an explicit tag name for the memory mapping. This tag name lets you have several memory mappings on the same file, but this functionality is rarely necessary. Calling mmap with only two arguments has the advantage of keeping your code portable between Windows and Unix-like platforms. On Windows, all memory mappings are readable and writable and shared between processes, so that all processes with a memory mapping on a file can see changes made by each such process.

On Unix-like platforms only, you can pass mmap.MAP_PRIVATE as the flags argument to get a mapping that is private to your process and copy-on-write. mmap.MAP_SHARED, the default, gets a mapping that is shared with other processes, so that all processes mapping the file can see changes made by one process (same as on Windows). You can pass mmap.PROT_READ as the prot argument to get a mapping ...