genpng.py

import struct
import binascii
import zlib

f = open('out.png', 'wb')
# Write PNG header
f.write(bytes([137, 80, 78, 71, 13, 10, 26, 10]))
# Write IHDR chunk
f.write(struct.pack('!I', 13)) # Chunk size
data = b'IHDR' + struct.pack('!IIBBBBB', 2, 2, 8, 6, 0, 0, 0)
f.write(data)
f.write(struct.pack('!I', binascii.crc32(data)))
# Write IDAT data

pixels = bytes([ 0, 255, 255, 255, 255, 0, 0, 0, 255,
                 0, 100, 42, 73, 255, 162, 255, 9, 255 ])
pixels = zlib.compress(pixels)
data = b'IDAT' + pixels
f.write(struct.pack('!I', len(pixels))) # Chunk size
f.write(data)
f.write(struct.pack('!I', binascii.crc32(data)))

# Write IEND
f.write(struct.pack('!I', 0))
data = b'IEND'
f.write(data)
f.write(struct.pack('!I', binascii.crc32(data)))

f.close()