mmap and shared memory

[Matias Surdi]

Suppose I've a process P1, which generates itself a lot of data , for 
example 2Mb.
Then, I've a process P2 which must access P1 shared memory and, 
probably, modify this data.
To accomplish this, I've been digging around python's mmap module, but I 
can't figure how to use it without files.

Could anybody explain me how could this be accomplished? An example will 
be very appreciated. Thanks a lot for your help.