Are Tuples In Python Immutable?

It says A tuple can not be changed in any way once it is created. But when I do the following: t1=(4,5,8,2,3) t1=t1+(7,1) print(t1) the tuple is changing to (4, 5, 8, 2, 3, 7,

Solution 1:

Yes, tuples are immutable; once created, they cannot be changed. t1=t1+(7,1) creates a new tuple and assigns it to the name t1. It does not change the tuple object originally referenced by that name.

Demo:

>>> t = (1, 2, 3)
>>> id(t)
4365928632
>>> t = t + (4, 5)
>>> id(t)
4354884624 # different id, different object

Solution 2:

yes they are immutable

t1 = t1 + (7,1)

Is creating a new tuple ... not modifying the old one

try

t1[0] = 5

Solution 3:

Basically when you call t1=t1+(7,1), you are reassigning t1 to a different memory location. What python means by immutable, is that you can't change them by slicing:

>>> t1=(4,5,8,2,3)
>>> t1[0] = 9
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> 

Because this creates a new tuple:

>>> t1=(4,5,8,2,3)
>>> id(t1)
4467745808
>>> t1 = t1+(9,)
>>> id(t1)
4468302112
>>> 

As you can see with lists, they keep the id:

>>> lst = [4, 5, 8, 2, 3]
>>> id(lst)
4468230480
>>> lst[0] = 6
>>> id(lst)
4468230480
>>> 

That is python's definition of immutability.

Solution 4:

I can't say Yes. Python tuples have a surprising trait: they are immutable, but their values may change. This may happen when a tuple holds a ref. to any mutable object, such as a dict, list...

>>> t1 = ('Bangalore', ['HSR', 'Koramangala'])
>>> print(t1)
('Bangalore', ['HSR', 'Koramangala'])
>>> print(id(t1)) # ID of tuple
4619850952

>>> place = t1[1]
>>> place.append('Silk Board')  # Adding new value to the list
>>> print(t1) 
('Bangalore', ['HSR', 'Koramangala', 'Silk Board'])
# Surprisingly tuple changed, let's check the ID
>>> print(id(t1)) # No change in the ID of tuple
4619850952

>>> print(t1[0])
Bangalore
>>> print(id(t1[0])) # ID of tuple's first element
4641176176
>>> print(id(t1[1])) # ID of tuple's second element (List)
4639158024
# These are the ref. id's of the tuple

>>> place.append('Agara')
>>> print(t1) 
('Bangalore', ['HSR', 'Koramangala', 'Silk Board', 'Agara'])
>>> print(id(t1))
4619850952
# Still no change, are they Immutable ??

>>> print(id(t1[1])) # The tuple having a ref. of Mutable object
4639158024

In the above example the id's of tuple and list didn't change. This is happening due to reference which is mapped to the tuple not the value.