Added fallback to type detection to allow automatic ENUM usage

[RobertoRoos]

+ Added exception raising for unknown types

Fixes #263 . The issue is almost three years old, but still relevant.

This allows using enums both with plc.read_by_name() and through AdsSymbol.read().

Tested the code with:

from pyads import Connection
import pyads


def main():
    plc = Connection(
        ams_net_id="127.0.0.1.1.1",
        ams_net_port=851,
    )

    variables = [
        "my_double",
        "my_enum",
        "my_double_array",
        "my_enum_array",
        "my_struct",
    ]

    with plc:

        for var in variables:
            try:
                value = plc.read_by_name(f"GVL_Main.{var}", cache_symbol_info=False)
            except pyads.ADSError as err:
                print("ERROR:", err)
            else:
                print("Value:", value)

        for var in variables:
            try:
                symbol = plc.get_symbol(f"GVL_Main.{var}")
                value = symbol.read()
            except pyads.ADSError as err:
                print("ERROR:", err)
            else:
                print("Value:", value)

    return


if __name__ == "__main__":
    main()

Output:

Value: 0.0 Value: 1 Value: [0.0, 0.0, 0.0, 0.0, 0.0] Value: [2, 2, 2, 2, 2] ERROR: ADSError: Failed to detect datatype for GVL_Main.my_struct Value: 0.0 Value: 1 Value: [0.0, 0.0, 0.0, 0.0, 0.0] Value: [2, 2, 2, 2, 2] ERROR: ADSError: Cannot read data with unknown datatype for symbol GVL_Main.my_struct (MyStructure)