Why use Inbuilt copy() function for sets in python when we can simply assign it? [duplicate]

Question

Given below is the code showing use of copy() function.

s = set([1, 2, 3, 4, 5])
t = s.copy()
g = s
print s == t  #Output: True
print s == g  #Output: True

What is use of copy() function when we can simply assign value of s in g?
Why do we have a separate function('copy') to do this task?

Answer 1

Continue with your example by modifying g: s will change, but t won't.

>>> g.add(4)
>>> g
set([1, 2, 3, 4])
>>> s
set([1, 2, 3, 4])
>>> t
set([1, 2, 3])

Answer 2

Because those two assignments aren't doing the same thing:

>>> t is s
False
>>> g is s
True

t may be equal to s, but .copy() has created a separate object, whereas g is a reference to the same object. Why is this difference relevant? Consider this:

>>> g.add(6)
>>> s
set([1, 2, 3, 4, 5, 6])
>>> t
set([1, 2, 3, 4, 5])

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