import arcpy

arcpy.env.workspace = "E:/lecture08data2"

fc = "airports.shp"
cursor = arcpy.da.UpdateCursor(fc, ["SIZE"], '"SIZE" = 'Large' and TOT_ENP > 100000 or "SIZE" = 'Small' and TOT_ENP < 100000')
for row in cursor:
    cursor.updateRow()

del row
del cursor