I was this days old when I learned about the setdefault method in the dict data type. This method keeps you from overwriting values in a dictionary if they have already been set. I can see instant use for this. You could implement read only keys or have a primary key like in a database.

The syntax for this is very similar to the update method, but only updates the dictionary if the key doesnt exist.

The help tells us:

dict.setdefault = setdefault(self, key, default=None, /)
    Insert key with a value of default if key is not in the dictionary.
    
    Return the value for key if key is in the dictionary, else default.

In practice it looks like.

mydict = {}
mydict.setdefault('first', 1)     # mydict == {'first': 1}
mydict.setdefault('first', '1st') # mydict == {'first': 1}