Immutability of tuples in Python3

Question

We know that tuple is immutable in Python. Then why the below code works?

3 * ('a','b','c')

Gives output as below:

('a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c')

Answer 1

You created a new tuple, see how id s differ:

>>> a = (1,2,3)
>>> id(a)
4505615456
>>> b = a * 3
>>> id(b)
4504578232

However, what you've accomplished will create also a new list if you did the equivalent:

>>> a = [ 1, 2, 3 ]
>>> id(a)
4505618120
>>> b = a * 3
>>> id(b)
4505618248

You can see the list is mutable with the following code:

>>> a = [ 1, 2, 3]
>>> id(a)
4505618568
>>> a.append(1)
>>> a.append(2)
>>> a.append(3)
>>> a
[1, 2, 3, 1, 2, 3]
>>> id(a)
4505618568

You can't achieve the same with a tuple.

One last thing to convince yourself that tuples are immutable:

>>> a = (1, 2, 3)
>>> a[0]
1
>>> a[0] = 10
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> a
(1, 2, 3)

versus the equivalent with a list:

>>> a = [1, 2, 3]
>>> a[0]
1
>>> a[0] = 10
>>> a
[10, 2, 3]

For more info and pitfalls, see this interesting article http://radar.oreilly.com/2014/10/python-tuples-immutable-but-potentially-changing.html

Answer 2

"Immutable" means "Can't be modified," not "Can't be used to construct other data." The latter wouldn't make much sense in a container, anyway! What use is there of a tuple other than containing data for later use?

Your sample code 3 * ('a', 'b', 'c') = ('a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c') just shows that multiplying a tuple by a scalar creates a new tuple with duplicating elements. The following is NOT possible however:

tup = ('a', 'b', 'c')
tup[0] = 'z'  # fails, because tuples are not mutable

Answer 3

`('a','b','c')` is a tuple.

And 3 * ('a','b','c')=('a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c') is another tuple which is made of 3 times of ('a','b','c') . If you think x =('a','b','c') then 3*('a','b','c') = x+x+x` (look, x and x+x+x is not same!).Both of them are separate tuples. In this similar rule 1 and 1+1+1 are not same!

You will find a proof in Benjamin Toueg's answer.