Names and mutation

A name points at an object. Two names can point at the same list. == compares values. is compares identity.

Two names, one list

a = ["Nairobi", "Mombasa"]
b = a
b.append("Kisumu")
print("a", a)
print("b", b)
print("same object", a is b)

b = a does not copy. It sticks a second name on the same list.

Values vs identity

a = ["Nairobi"]
b = ["Nairobi"]
print("equal", a == b)
print("same", a is b)

Equal contents, two objects.

Copy

a = ["Nairobi", "Mombasa"]
b = list(a)
b.append("Kisumu")
print("a", a)
print("b", b)
print("same object", a is b)

list(a) is a shallow copy: a new list, same items inside. Enough when the items are strings.