> ctypes.windll.kernel32.VirtuAlloc function return by default 
> a ctypes.c_long

In Windows, ctypes.c_int is an alias for ctypes.c_long, which is a signed 32-bit integer. This is the default conversion type for the integer parameters of an FFI (foreign function interface) call, as well as the result. It's up to the author of a library wrapper to define the correct function prototypes, pointer types, and aggregate struct/union types. Some common Windows types are defined/aliased in the ctypes.wintypes module, but none of the API is prototyped.

> ctypes.windll.kernel32.VirtuAlloc

I suggest avoiding the global ctypes.windll loader. IMO, it's not a great idea to use a global library loader since it caches WinDLL instances, which cache function pointer instances. This make it possible for unrelated projects to interfere with each other and the main script by defining incompatible function prototypes -- particularly for common Windows API functions. It also doesn't allow passing use_last_error=True to enable the safe capturing of the thread's last error value as ctypes.get_last_error().

I recommend creating individual CDLL / WinDLL instances. For example:

    import ctypes

    kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)

    kernel32.VirtualAlloc.restype = ctypes.c_void_p
    kernel32.VirtualAlloc.argtypes = (
        ctypes.c_void_p, # lpAddress
        ctypes.c_size_t, # dwSize
        ctypes.c_ulong,  # flAllocationType
        ctypes.c_ulong)  # flProtect

If the call fails, you can raise an OSError as follows:

    base_addr = kernel32.VirtualAlloc(None, size, alloc_type, protect)
    if base_addr is None:
        raise ctypes.WinError(ctypes.get_last_error())