Graphing your data using package memory_graph can help your understanding of the Python Data Model:

import memory_graph as mg # see link above for install instructions

arr1 = []
arr2 = [1, 2]
arr1.append(arr2)
arr2[0] = 5  # change of value
mg.render(locals(), 'graph1.png')  # graph the local variables

A change of a value of mutable type list effects all that share the value, arr1 and arr2.

arr2 = [6]   # name rebinding 
print(arr1)
mg.render(locals(), 'graph2.png')  # graph the local variables

Name rebinding only effects the arr2 variable that is rebound.