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)

[coveralls]

Pull Request Test Coverage Report for Build 10661739215

Details

• 30 of 33 (90.91%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 95.014%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyads/symbol.py	23	24	95.83%
pyads/connection.py	7	9	77.78%

Totals
Change from base Build 10633721828:	0.06%
Covered Lines:	1753
Relevant Lines:	1845

---

💛 - Coveralls

[chrisbeardy]

thanks @RobertoRoos , just had a look at this, I'm generally happy with this implementation. Could you just solve the conflict, please. I've also left a comment too in the review. It may be worth a few more tests, either unit or manual, to make sure we haven't broken any other edge cases such as when the user does pass in the type, or the wrong type etc. Also, maybe when structures are passed in, I wonder how it will handle ENUMS in structures....(not sure if that is possible in the struct def actually).

Can't see any reason why it would have broken anything else but being paranoid.

[RobertoRoos]

@chrisbeardy you mentioned more tests might be a good idea. What cases would you like to be covered? I'm not sure what is needed exactly.