How to convert 4 bytes to an integer ?

[GiggsB]

I used python 3 to execute the code.

This time instead of sending [255,15,0,0] from slave, I am sending [0,0,15,255] and on RP, I receive data as

.
.
[0,0,15,255]
[255,255,0,0]
.
.

This works but it doesn't makes sense, why. Also, IDK why this second set of 8-bit integers is very different from what I expect.