The "simple microprocessor" is a test-driven development approach to the implementation of a model of a very basic microprocessor in Python 3. It's purpose is to illustrate the basic components of a hardware microprocessor, such as simple instructions, memory, registers and the instruction pointer. You can find a video showing the development at https://youtu.be/fjcnyh6mBV8.
Here's a very simple program to add two numbers in memory positions [0] and [1].
MOV 0, 5
MOV 1, 3
INC 0
DEC 1
MOV r0, [1]
JNZ 2
MOV r0, [0]
Basically, it keeps incrementing by one the value in memory position [0] and decrementing by 1 the value in memory position [1] until value in [1] reaches zero. At that point [0] has the sum of both values.
You can find other runnable programs in samples.py, and the tests in tests.py. Check the default "assembly" program in simproc.py main function.