This is a partial snippet, so there may be some missing/undefined parts

ctypes_example.py

from ctypes import CFUNCTYPE, c_int, POINTER, byref, c_char_p, c_har, c_vooid_p, c_uint

# SOURCE: https://docs.nvidia.com/deploy/nvml-api/group__nvmlDeviceQueries.html

class nvmlPciInfo_t(Structure):
    _fields_ = [
        ("bus", c_uint),                                                    # 0 to 0xff
        ("busId", c_char * NVML_DEVICE_PCI_BUS_ID_BUFFER_SIZE),             # string + 0x00
        ("busIdLegacy", c_char * NVML_DEVICE_PCI_BUS_ID_BUFFER_V2_SIZE),    # string + 0x00
        ("device", c_uint),                                                 # 0 to 31
        ("domain", c_uint),                                                 # 0 to 0xffffffff
        ("pciDeviceId", c_uint),                                            # 16-bit device id + 16-bit vendor id
        ("pciSubSystemId", c_uint),                                         # 32-bit id
    ]

    
nvmlDeviceInfo_t = c_void_p


def nvml_device_get_handle_by_pci_bus_id_v2(pci_bus_id):
    proto = CFUNCTYPE(
        c_int,
        c_char_p,
        nvmlDeviceInfo_t
    )

    params = (1, "pci_bus_id", 0), (1, "device_handler", 0),

    func = proto(("nvmlDeviceGetHandleByPciBusId_v2", nvml_lib), params)

    #pci_bus_id = c_char_p(pci_bus_id) # + b"\0"
    device_handler = nvmlDeviceInfo_t()
    ret_code = func(pci_bus_id, byref(device_handler))

    if ret_code == NVML_SUCCESS:
        return device_handler
    else:
        raise Exception(f"Err {ret_code}: {nvml_error_string(ret_code)}")


def nvml_device_get_pci_info_v3(device_handler):
    proto = CFUNCTYPE(
        c_int,
        nvmlDeviceInfo_t,
        POINTER(nvmlPciInfo_t)
    )

    params = (1, "device_handler", 0), (1, "pci_info_struct", 0),

    func = proto(("nvmlDeviceGetPciInfo_v3", nvml_lib), params)

    pci_info = nvmlPciInfo_t()
    ret_code = func(device_handler, byref(pci_info))

    if ret_code == NVML_SUCCESS:
        return pci_info
    else:
        raise Exception(f"Err {ret_code}: {nvml_error_string(ret_code)}")

def nvml_device_get_handle_by_index_v2(device_index):
    proto = CFUNCTYPE(
        c_int,
        c_uint,
        POINTER(nvmlDeviceInfo_t)
    )

    params = (1, "device_index", 0), (1, "device_handler", 0),

    func = proto(("nvmlDeviceGetHandleByIndex_v2", nvml_lib), params)

    device_handler = nvmlDeviceInfo_t()
    ret_code = func(c_uint(device_index), byref(device_handler))

    if ret_code == NVML_SUCCESS:
        return device_handler
    else:
        raise Exception(f"Err {ret_code}: {nvml_error_string(ret_code)}")
        
if __name__ == "__main__":

    device_handler = nvml_device_get_handle_by_index_v2(0)

    pci_info = nvml_device_get_pci_info_v3(device_handler)