Why list, dictionary and tuple are taken value vice versa when declare it in one-line?

Question

I am feeling very strange when I am working on list, dictionary and tuple in python.

When we declare multiple variable in one line like a = b = c = 0 it behaves like separate variables.

If we are update value any of the above variables then it will not affect another variable like below.

a = 10
b = 11
c = 13

But, this thing is not applying with list, tuple and dictionary. If we declare blank list like below.

a = b = c = []

Now, I am appending a value to only a list.

a.append('Testing')

Now, b and c are automatically assigned that value.

This thing also happens with dictionary and tuple also.

I have to know that why it is not accept to declare it like above example.

If you declare `a = b = c = ANYTHING`, you are **always** assigning the same object to three variables. It is not different between numbers and tuples and lists and dictionaries. But for tuples and numbers, it doesn't matter, because they are immutable. — khelwood, Dec 19 '19 at 13:47
I know that Please read whole question and test in terminal. — Mayur Jotaniya, Dec 19 '19 at 13:48
"Can anyone please help to solve this issue". This is not a question. What is your question? There are several ways to declare 3 lists on the same line. another example: `a = []; b = []; c = []` — Jean-François Fabre, Dec 19 '19 at 13:52
`I know that`—Not according to what you wrote in your question. — khelwood, Dec 19 '19 at 13:59
`a = 10` is *assigning a new value to the variable* - the previous value of the variable is not relevant. But `a.append('Testing')` is *modifying an existing value* - a value which has two other names referring to it, so the change is equally visible via those names. — jasonharper, Dec 19 '19 at 15:11
Possible duplicate? [Immutable vs Mutable types](https://stackoverflow.com/q/8056130/4518341) — wjandrea, Dec 19 '19 at 15:25

score 1 · Accepted Answer · edited Dec 19 '19 at 15:36

This is a concept of mutable and immutable objects. When you write a code like a = b = c = [], all the variables are referencing the same object. If this object is mutable, when you change the object from any of the variables, the other two variables will reflect the change too. Some object types are mutable, others not.

You can read the article bellow to have a more complete answer.

https://medium.com/@meghamohan/mutable-and-immutable-side-of-python-c2145cf72747

Why list, dictionary and tuple are taken value vice versa when declare it in one-line?

1 Answers1