Code in field calculator does not 'refresh'

[AndersKMG]

Hello. I have a python code in the ArcMap field calculator that translates numbers in the Id-column  to text in another column in the same attribute table. In the pre-logic-script It looks like this:

def reclass(Id):
    if (Id == 0):
        return "AAA"
    if (Id == 1):
        return "BBB"
    if (Id == 2):
        return "CCC"
    if (Id == 3):
        return "DDD"
    if (Id == 4):
        return "EEE"
    if (Id == 5):
        return "FFF"
    if (Id == 6):
        return "GGG"
    else:
        return "<Null>"

and in the other box:

reclass(!Id!)

The problem is that this code disapears every time I shut down arcMap, and have to be re-loaded when I add anything. For example if I add an object with id-class 2 it doesn't automatically writes CCC in the new column iuntill I have re-runed the script.

Is there some way I can automatically run this script as soon as I open / change anything the attribute table? 

[JohannesLindner]

For ArcMap, there's the Attribute Assistant.

For ArcGIS Pro, there are Attribute Rules.

[BlakeTerhune]

Attribute Rules in ArcGIS Pro is the best solution here. I will add that you can write a Python script that to perform the calculate field operation on your data and schedule it to run as a task. So every night, or even every hour, the script could run to calculate the values.

[Anonymous User]

Two tips for you: using "<Null>" will enter it as a string and not a true Null.

You can avoid chaining if statements by using a switch case (dictionary lookup) construct.

def reclass(Id):
    classDict = {
        0: "AAA",
        1: "BBB",
        2: "CCC",
        3: "DDD",
        4: "EEE",
        5: "FFF",
        6: "GGG"}

    return classDict.get(Id) # <- returns the value if found in the dictionary or the default true Null

    #return classDict.get(Id, '<Null>') # <- returns the value if found in the dictionary or the string <Null> as the default