Not getting the desired output when using the Python list

Question

When I run this code, output is 11, but my expected output is 10.

a=[10]
b=a
b[0]=11
print(a)

What's the issue? And how do I get my expected output without importing any external module?

Answer 1

It's because b is a reference to a. Changing any element of a or b are affecting the whole a and b list. To keep the list a always the same, Copy a to b then changing won't affect to a.

a = [10]
b = a.copy() # Also can slice it by b = a[:]
b[0] = 11
print(a)