Most users are familiar with creating their own attributes within objects within an Aimsun model. These will typically be numbers or strings but it is also possible to add a column to an object where a value is returned based on some Python Code, allowing a value to be calculated on the fly.

A simple example is one that places a label letter on a turn to say whether it is Left, Through, Right or U-Turn.

Click to enlarge: Showing the attribute in the network

Firstly we could create this column using the Types Editor (by selecting the relevant object type from the Types window), then adding a new column of Column Type Function, in this case one that returns a string as a result.

Click to enlarge: Create the column using the Types Editor

The function needs to contain a Python function with signature of the form:

def eval_attr(object):

which returns a value with the result.

Here is the code we store inside the column

def determineTurningLetterForAngle(angle):
	dirString = ""
	if abs(angle)<30.0: dirString+="T" elif abs(angle)>150.0:< dirString+="U" elif angle>0.0:
		dirString+="L"
	else:
		dirString+="R"
	return dirString

def retrieveTurningLetterForTurning(turning):
	angle = turning.calcAngleSections()
	directionString = determineTurningLetterForAngle(angle)
	return directionString
	
def eval_attr(object):
	res = retrieveTurningLetterForTurning(object)
	return res

However we can create all this from a script which creates the column, and populates the code.
The code to set up the column directly from a Python script is as follows:

def main():
	turnLetterAttr = model.getColumn("GKTurning::TurnLetter")
	if turnLetterAttr == None:
		turningType = model.getType("GKTurning")
		turnLetterAttr = 
turningType.addColumn("GKTurning::TurnLetter","TurnLetter", 
GKColumn.String, GKColumn.ePython)
	turnLetterAttr.setPythonCode(PYTHON_CODE_STRING)

main()

PYTHON_CODE_STRING contains the definition of the function.

Download Python script for creating a turning classification label