Converting ModelBuilder Value to a String in Python to use in Calculate Field Expression

Question

I am trying to take a Value from a ModelBuilder Feature Selection Iterator and pass it to the Calculate Field Python Expression in order to write values to the field of a feature selection in ArcGIS Pro 2.9.0.

My model iterates over the Features in Gridline_Grid by PageName, Value becomes the PageName Value. Then that Selected Feature is used to Select By Location all the NRN_Anno features intersecting it. Then the Selection has it's field GRIDS calculated using a Python expression that is designed to look at GRIDS and if it is 0 recalculate it to %Value% (the value from the iterator) if it is not 0 pass the current GRID value to a concatenate expression with %Value% and recalculate the field to a concatenation of both values.

def reclass(GRIDS):
if (GRIDS == '0'):
    return str(%Value%)
else:
    return (GRIDS)+', '+ str(%Value%)

The model keeps telling me the Value sotred in %Value% is not defined. This is telling me that python is returning the value from the parameter %Value% but I cannot seem to get it to read it as a string.

What am I doing wrong?

Answer 1

Apparently '%Value%' works... not sure why.

def reclass(GRIDS):
    if (GRIDS == '0'):
        return '%Value%'
    else:
        return (GRIDS)+', '+ '%Value%'

Answer 2

Adding on to your answer, the note in the Inline variable substitution states:

"You must enclose inline variables that are strings within quotation marks ('%string variable%') in an expression. Inline variables that are numbers do not require quotation marks."