Seeing how reading an image file from disk compares to constructing it in memory

memory_vs_disk.py

import io
import os
import tempfile
import timeit


# A valid PNG file.
png_bytes = (
    '\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x00\x01\x00\x00\x00\x01\x08'
    '\x06\x00\x00\x00\x1f\x15\xc4\x89\x00\x00\x00\nIDATx\x9cc\x00\x01\x00\x00'
    '\x05\x00\x01\r\n-\xb4\x00\x00\x00\x00IEND\xaeB`\x82'
)
png_len = len(png_bytes)

# Create the image on disk.
_, filename = tempfile.mkstemp(suffix='.png')

with open(filename, 'wb') as fh:
    fh.write(png_bytes)


def read_from_disk(filename):
    with open(filename) as fh:
        data = fh.read()
        assert len(data) == png_len


def read_from_memory(filename):
    fh = io.BytesIO(png_bytes)
    data = fh.read()
    assert len(data) == png_len


setup = 'from __main__ import read_from_disk, read_from_memory, filename'
statements = ['read_from_memory(filename)', 'read_from_disk(filename)']

for s in statements:
    timer = timeit.Timer(s, setup=setup)
    print s, timer.repeat()


os.unlink(filename)

results.sh

$ python2.7 memory_vs_disk.py 
read_from_memory(filename) [1.0891728401184082, 1.0940730571746826, 1.105133056640625]
read_from_disk(filename) [11.179327011108398, 10.985939025878906, 11.328207969665527]