Simulating C#'s sbyte (8 bit signed integer) casting in Python

Question

In C#, I can cast things to 8bit signed ints like so:

(sbyte)arg1;

which when arg1 = 2, the cast returns 2 also. However, obviously casting 128 will return -128. More specifically casting 251 will return -5.

What's the best way to emulate this behavior?

Edit: Found a duplicate question: Typecasting in Python

s8 = (i + 2**7) % 2**8 - 2**7      // convert to signed 8-bit

Answer 1

With ctypes:

from ctypes import cast, pointer, c_int32, c_byte, POINTER
cast(pointer(c_int32(arg1)), POINTER(c_byte)).contents.value

Answer 2

I'd use the struct module of the Python standard library, which, as so often, comes in handy for turning values into bytes and viceversa:

>>> def cast_sbyte(anint):
    return struct.unpack('b', struct.pack('<i', anint)[0])[0]
... ... 
>>> cast_sbyte(251)
-5