What is difference in simple arr1 = arr2 and arr1 = arr2[:]?

Question

when I use [:] is it copy of values and without using it is it taking the reference and changing the value?

Answer 1

This depends critically on the object being sliced. Frequently, [:] gives you a shallow copy:

a = [1, 2, 3]
b = a[:]
# `b` is distinct from `a`, but `b` references the same objects that `a` does.
print(b is a)  # False
print(all(x is y for x, y in zip(a, b))  # True

but it's easy to write a pathological object which just returns the object itself:

class SliceMe(object):
    def __getitem__(self, obj):
        return self