When you want to increment or decrement, you typically want to do that on an integer. Like so:
But in Python, integers are immutable. That is you can't change them. This is because the integer objects can be used under several names.
So you have to reassign. Like this:
b = b + 1
b += 1
Which will reassign b to b+1. That is not an increment operator, because it does not increment b, it reassigns it.
In short: Python behaves differently here, because it is not C, and is not a low level wrapper around machine code, but a high-level dynamic language, where increments don't make sense, and also are not as necessary as in C, where you use them every time you have a loop.