I have 2 lists:
a = [1, 2, 3, 4, 5]
b = [9, 8, 7]
I performed the following two operations and tried printing each list
a.append(b)
b.append(a)
print(a) # Expected Result: [1, 2, 3, 4, 5, [9, 8, 7]]
print(b) # Expected Result: [9, 8, 7, [1, 2, 3, 4, 5]]
But the result turned out to be:
a = [1, 2, 3, 4, 5, [9, 8, 7, [...]]]
b = [9, 8, 7, [1, 2, 3, 4, 5, [...]]]
Can someone explain in detail what exactly is happening here?
I tried printing each element of the list but the list keep on going without any end.
Python lists are stored by references. You add such reference to the lists, which can be still modified in another place. After a.append(b) you've got [1, 2, 3, 4, 5, b]. That b has value [9,8,7] at the moment, but when you b.append(a), you change the value of it to [9, 8, 7, a]. And that a happens to contain b, and so on ending up with cycle of two lists contained in each other. If you want to avoid that, you need to make a copy of list you want to append. A copy will make it so changes to original list are not reflected in the copy.
a = [1,2,3,4,5]
b = [9,8,7]
a_copy = a.copy()
b_copy = b.copy()
a.append(b_copy)
b.append(a_copy)
print(a) # Expected Result: [1,2,3,4,5,[9,8,7]]
print(b) # Expected Result: [9, 8, 7 ,[1,2,3,4,5]]