uri = '/Users/ep9k/Desktop/SandraMonson/TestZips.shp'
join_layer = iface.addVectorLayer(uri, 'Patients by Zip Code', 'ogr')
target_field = 'Patient_Da'

def apply_graduated_symbology():

    myRangeList = []

    symbol = QgsSymbol.defaultSymbol(join_layer.geometryType())
    symbol.setColor(QColor("#f5c9c9"))
    myRange = QgsRendererRange(0, 3, symbol, '0-3')
    myRangeList.append(myRange)

    myRenderer = QgsGraduatedSymbolRenderer(target_field, myRangeList)
    myRenderer.setMode(QgsGraduatedSymbolRenderer.Custom)

    join_layer.setRenderer(myRenderer)

    print(f"Graduated color scheme applied")

apply_graduated_symbology()

myRange = QgsRendererRange(0, 3, symbol, '0-3')

#set precision of myRange   (myRange.setPrecision doesn't work)

myRangeList.append(myRange)