How to access a nested structure using PyADS - plc

Question

I have two structures defined in TwinCAT3 like so:
TYPE ADSUWDisplay :
STRUCT
sYarn : STRING;
sNextYarn : STRING;
lLength : REAL;
iPosition : INT;
sYarnSpec : STRING;
iPackageCount : INT;
iPackageTotalCount : INT;
iCount : INT;
iTotalCount : INT;
sUpcomingYarn : STRING;
sUpcomingYarnSpec : STRING;
sUWMessage : STRING;
sThreadUp : STRING;
END_STRUCT
END_TYPE
TYPE ADSRemoteDisplay :
STRUCT
iUW : INT;
iCount : INT;
sState : STRING
iStateNo : INT;
sRobotMessage : STRING;
adsUWDisplay : ARRAY[0..5] OF ADSUWDisplay;
END_STRUCT
END_TYPE
As you can see, ADSUWDisplay is nested inside ADSRemoteDisplay.
How can I access ADSUWDisplay using PyADS?
More specifically, how do I declare my Structure defs for use in pyads.connection.read_structure_by_name()?
Please help!
Thanks

Answer 1

You can read out a struct as follows, from the pyads docs:
Use the parameter structure_def to define the structure and array_size to define the size of the array.
>>> structure_def = (
("i", pyads.PLCTYPE_INT, 1),
("s", pyads.PLCTYPE_STRING, 1)
)
>>> symbol = plc.get_symbol("MyStructure", structure_def=structure_def, array_size=2)
>>> symbol.write([{"i": 1, " "s": "foo"}, {"i": 2, "s": "bar"}])
>>> symbol.read()
[{"i": 1, " "s": "foo"}, {"i": 2, "s": "bar"}]
Not sure how to define a nested struct. I guess you can try to add a nested tuple in structure_def, e.g.:
structure_def = (
("i", pyads.PLCTYPE_INT, 1),
(
("s1", pyads.PLCTYPE_STRING, 1),
("s2", pyads.PLCTYPE_STRING, 1)
)
)