A variable holds a reference to an object. You can see the reference with id(varaible). The string object that you have a reference to is immutable. When you reassign the variable to a new string, the reference is updated to point to a new string object, and the old string object is unchanged. Edit: Note that assignment assigns a reference. No matter whether the object being referred to is mutable, assignment to a variable updates the variable's reference. Mutating an object means changing the data held within an object in place - i.e. its reference does not change when mutated. Answer from Goobyalus on reddit.com
Reddit
reddit.com › r/learnprogramming › what does 'strings are immutable' mean?
r/learnprogramming on Reddit: What does 'Strings are immutable' mean?
September 29, 2022 -
I'm using Treehouse for Python basics and the tutor mentions this in the context of reassigning a value to a string variable. But if the value of the string variable can be reassigned, what does it mean to say it's immutable? Is there something I'm just not getting? Thanks.
Top answer 1 of 8
6
A variable holds a reference to an object. You can see the reference with id(varaible). The string object that you have a reference to is immutable. When you reassign the variable to a new string, the reference is updated to point to a new string object, and the old string object is unchanged. Edit: Note that assignment assigns a reference. No matter whether the object being referred to is mutable, assignment to a variable updates the variable's reference. Mutating an object means changing the data held within an object in place - i.e. its reference does not change when mutated.
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A variable in Python holds a reference to an object, not the object itself. So reassigning a variable is different from modifying an object. If you have a variable that points to a string, you can reassign it to point to a different string, but you can't modify the string itself. The flip-side of this is that you never have to worry about a string changing unexpectedly because some other part of your program holds a reference to it. In contrast, if you have a mutable object like a list, this kind of thing can happen: >>> list1 = [] >>> list2 = list1 # both variables point to the same list >>> print(list1 is list2) True >>> list1.append(123) >>> print(list1) [123] >>> print(list2) [123]
This may be a stupid question but how are strings “immutable” if I can do “str += ‘foo’“ ? Nov 8, 2018
r/learnpython 7y ago
Top answer 1 of 16
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First a pointed to the string "Dog". Then you changed the variable a to point at a new string "Dog eats treats". You didn't actually mutate the string "Dog". Strings are immutable, variables can point at whatever they want.
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The string objects themselves are immutable.
The variable, a, which points to the string, is mutable.
Consider:
a = "Foo"
# a now points to "Foo"
b = a
# b points to the same "Foo" that a points to
a = a + a
# a points to the new string "FooFoo", but b still points to the old "Foo"
print a
print b
# Outputs:
# FooFoo
# Foo
# Observe that b hasn't changed, even though a has.
Videos
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Why Python strings are immutable? #coding #pythonprogramming - YouTube
Is A Python String Immutable
Austin Z. Henley
austinhenley.com › blog › pythonstringsaremutable.html
Python strings are immutable, but only sometimes - Austin Z. Henley
February 15, 2021 - The standard wisdom is that Python strings are immutable. You can't change a string's value, only the reference to the string.
Reddit
reddit.com › r/learnpython › is there any particular reason why strings are immitable?
r/learnpython on Reddit: Is there any particular reason why strings are immitable?
August 16, 2024 -
I think it could be very useful to have strings mutable. We could to this:
However, I guess there is a reason why strings are immutable. I wonder why?
str = 'apple' str[0] = 'A'
Top answer 1 of 13
93
One big reason is performance - strings are used very often, so Python is able to do many optimizatioms that won't be possible if strings were mutable. Eg. String Interning - Python internally caches many small strings to reduce memory usage. Another reason is ease of use. If strings were mutable, then they won't be hashable so we won't be able to use strings as dict keys. Usually you won't need to mutate strings since strings have many useful immutable methods. If you still need mutability for some reason, then you can maintain a list of strings (each element in list is a word or character). Then after mutation is done, convert your list back to string using str.join().
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Because strings are mostly used as values, not as references. fruit = 'apple' frist_ingridient = fruit #apple recipe = f'Put one {fruit} on a plate' print(frist_ingridient, recipe) #apple Put one apple on a plate fruit[0] = 'A' #we don't change frist_ingridient or recipe here print(frist_ingridient, recipe) #Apple Put one apple on a plate - frist_ingridient has changed!
GeeksforGeeks
geeksforgeeks.org › python › why-are-python-strings-immutable
Why are Python Strings Immutable? - GeeksforGeeks
October 13, 2025 - Strings in Python are "immutable" i.e. they cannot be changed after they are created. Strings are immutable by design to keep them safe, consistent, and efficient.
Runestone Academy
runestone.academy › ns › books › published › py4e-int › strings › immutable.html
7.5. Strings are immutable — Python for Everybody - Interactive
The reason for the error is that strings are immutable, which means that you can’t modify an existing string.
Medium
medium.com › @sking5006j › why-strings-are-immutable-in-python-91eb3a6dcecc
Why Strings Are Immutable in Python | by MOHAMMAD SUFIYAN SHAJAHAN SHAIKH | Medium
October 29, 2025 - In Python, everything is an object — integers, lists, and strings. Each object has a type, identity, and value. When we say strings are immutable, it means their value cannot be altered after creation.
Reddit
reddit.com › r/learnpython › why python strings are immutable?
r/learnpython on Reddit: Why python strings are immutable?
August 3, 2022 -
Why they made strings like this? What was the issue not creating them mutable like other iterables ie lists? Is it implemented intentionally in this way for some reason, or they made it like this due to some implementation issue ( it become compulsion on them to do it, or optimization issue )?
Top answer 1 of 4
9
So they can guarantee a constant hash value and can therefore be used as keys in dictionaries I guess. All of Python is built on top of dictionaries, so it would make sense.
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Well, immutability is overall a good thing. It prevents many dumb mistakes, for one, and since immutable types' methods return new instances, method chaining is not only possible but easy and "safe". Say strings were mutable. You could no longer use them as dictionary keys, which would make JSON parsing much more annoying and less intuitive. It would also mean that you'd have to treat them with care just like lists because, while assigning immutable references is in practice not really different from copying values, with mutable types you run the risk of mutating values you never intended. You would have to start explicitly copying strings, which is not intuitive especially to newcomers.
Runestone Academy
runestone.academy › ns › books › published › FOPP-PIE › sequences_immutable-strings.html
9.3 Immutable Strings
What does that mean? When something is mutable it can change. When something is immutable, it cannot change. So, when we create a string, some memory is allocated to store that string. When we want to change that string, we have to actually create a new string.
Medium
medium.com › @mvenkatashivaditya › why-are-strings-immutable-in-python-bfdbf1c1199a
Why Python Strings Are Immutable — and Why It Matters | by Shivaditya Meduri | Medium
May 13, 2025 - TL;DR — Python strings are immutable so that their hash value can be cached and to enable safe, efficient use as dict/set keys
Sololearn
sololearn.com › en › Discuss › 1323097 › python-strings-are-immutable
Python strings are immutable? | Sololearn: Learn to code for FREE!
Strings are immutable in Python. t1="abcde" t2=t1.replace("b", "B") print(t1) #abcde print(t2) #aBcde As you can see, the replace method doesn't change the value of the string t1 itself. It just return a new string which can be used for other purposes.
Kadenfrisk
python.kadenfrisk.com › strings in python › string immutability
Python String Immutability | Fluffy's Python Course
In Python, strings are immutable. This means that once a string object is created, its content cannot be changed.
TutorialsPoint
tutorialspoint.com › python_text_processing › python_string_immutability.htm
Python Text Processing - String Immutability
In python, the string data types are immutable. Which means a string value cannot be updated. We can verify this by trying to update a part of the string which will led us to an error.
Hacker News
news.ycombinator.com › item
All strings in python are immutable, as an example. | Hacker News
July 25, 2025 - The standard library also has String, CString, CStr, OsString, and OsStr · The latter four are for niche situations. 99.9% of the time, it's similar to Java: &str is Java's String, String is Java's StringBuffer/StringBuilder
EyeHunts
tutorial.eyehunts.com › home › strings are immutable in python | example code
Strings are immutable in Python | Example code
July 27, 2022 - Immutable objects are once created, will not change in their lifetime. Python strings are immutable. You can't change the value of the string
Fatos Morina
fatosmorina.com › home › unveiling the immutable nature of strings in python
Unveiling the Immutable Nature of Strings in Python - Fatos Morina
July 2, 2023 - Strings are a fundamental data ... understand that strings in Python are immutable. This means that once a string is created, it cannot be modified in-place....
Educative
educative.io › answers › why-are-strings-in-python-immutable
Why are strings in Python immutable?
In Python, strings are made immutable so that programmers cannot alter the contents of the object (even by mistake).
Medium
medium.com › nerd-for-tech › why-string-is-immutable-python-bfd934e09f19
The Unchanging Beauty: The Whys and Hows of Immutable Strings in Python | by Shilpa Sreekumar | Nerd For Tech | Medium
November 24, 2023 - The string data type is immutable in Python, meaning it is unable to be changed. As a result, the value of a string cannot be altered in Python.
Hacker News
news.ycombinator.com › item
Python strings are immutable, but only sometimes | Hacker News
February 16, 2021 - This is an undocumented optimization, so you should assume you're allocating a new sting every single time like the internet says · I've been coding Python since 1.5.2 days and so I'll continue to use lists as intermediate string builders and then join afterwards because I know this works ...
CodingNomads
codingnomads.com › python-string-immutability
Python Immutability
Python strings are immutable, which means that you can't change a string after you created it.