A += operator that works for both strings and ints

Is there a way in Python to initialize a variable so that it will work with += "a string" or with += 100?
For example:

a = <what to put here>
a += 100 # a = 100
b=<same what to put here from above>  
b+="a string" # b = "a string"

If I use:

a = ""
a += "a string" # this will work fine
b = ""
b += 0 # -> TypeError

Once the type of the variable has been defined, it is okay to get a TypeError afterwards if I try to += a different type. For example:

a = <what to put here>
a += "a string" # a = "a string"
a += 200 # -> okay to get a TypeError here

I’m only interested in making this work for ints and strings.

>Solution :

a = type('', (), {'__add__': lambda _, x: x})()
a += 100

b = type('', (), {'__add__': lambda _, x: x})()  
b += "a string"

print([a, b])

Output (Attempt This Online!):

[100, 'a string']