Simple cases of item assignment don't require much explanation: X[2] += 1 makes an increment to the third item of list X (or if X is a dictionary, to the item that has 2 as its key). Less obvious are assigments using multiple indices:

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A = [2,1,5]
B = [False,1,7]
C = list(range(20))
D = [A,6,0,B,"thing",C]
B[0] = D[3][2] 
D[5][2] = "stop"
D[4][0] = 'J'
D[3] += 8
D[4] *= 0 
D[2] += [9]

Some of these assignments are Python errors: