Immutability of dictionary keys in python

Question

dic={}
dic[1]=100
dic[2]=200
dic[1]+=500

here I have initialed a dictionary and I am able to update the key value of the dictionary. But keys in dictionary are immutable, so what's actually happening, can someone please tell?

Answer 1

Just think of it this way. We have an empty dictionary:

d = {}

If we do this:

d[1] = 100

we are simply adding a key and assigning a value to that key, right then and there.

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Just like sets, dicts cannot have duplicate keys, so adding another key with the same name will overwrite the original.

Like doing calling d[1] = 200 will overwrite the original d[1] .

d[1] += 500 is the same as:

d[1] = d[1]+500

where we are simply telling python to add a key to d called 1 , and assign the value of the original key plus 500 to that key.