Is there a faster way to copy from a bytearray to a mmap slice in Python?

Question

I am writing code for an addon to XBMC that copies an image provided in a bytearray to a slice of a mmap object. Using Kern's line profiler, the bottleneck in my code is when I copy the bytearray into the mmap object at the appropriate location. In essence:

length = 1920 * 1080 * 4
mymmap = mmap.mmap(0, length + 11, 'Name', mmap.ACCESS_WRITE)
image = capture.getImage()  # This returns a bytearray that is 4*1920*1080 in size
mymmap[11:(11 + length)] = str(image)  # This is the bottleneck according to the line profiler

I cannot change the data types of either the image or mmap. XBMC provides the image as a bytearray and the mmap interface was designed by a developer who won't change the implementation. It is NOT being used to write to a file, however - it was his way of getting the data out of XBMC and into his C++ application. I recognize that he could write an interface using ctypes that might handle this better, but he is not interested in further development. The python implementation in XBMC is 2.7.

I looked at the possibility of using ctypes (in a self-contained way withing python) myself with memmove, but can't quite figure out how to convert the bytearray and mmap slice into c structures that can be used with memmove and don't know if that would be any faster. Any advice on a fast way to move these bytes between these two data types?

Answer 1

If the slice assignment to the mmap object is your bottleneck I don't think anything can be done to improve the performance of your code. All the assignment does internally is call memcpy.