working_with_bytes.py

# In case you need byte arrays
import numpy as np
a = np.uint64(7640891576956014592) #64 bits
b = a.tostring() # '\x00\xd0\xbc\xf3g\xe6\tj' in bytes
b = bytearray(b) # bytearray(b'\x00\xd0\xbc\xf3g\xe6\tj') Byte array object


# Padding
a = [1, 1, 1, 1, 1]
a + [0] * (16 - len(a)) # [1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

# From string of text into padded bytes
s = 'abc'
s = s + chr(0) * (128 - len(s))
b = struct.unpack('<16Q', s)

#Packing
struct.pack('<16Q', *b)