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.
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. Like so: ... Which implies that each time you make a change to a string variable, you are actually producing a brand ...
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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
15:15
string in python |"Is String Mutable in Python? | Python Programming ...
08:04
Python strings, immutability, and += - YouTube
01:40
Python Beginners – Why Strings Are Immutable? - YouTube
Mutability in Python.
06:02
What does "mutable" mean in Python? - YouTube
01:00
Python's Immutable Strings vs Mutable Lists: A Student's Discovery ...
Can I modify a string in Python?
No, you cannot modify a string directly. Any change creates a new string, and the original remains unchanged.
guvi.in
guvi.in › blog › python › is a string mutable in python? let’s have a look at the concept
Is a String Mutable in Python? Let’s Have a Look
Why are Python strings immutable?
Python strings are designed to be immutable to make them more reliable, efficient, and safe, especially when used in memory or as dictionary keys.
guvi.in
guvi.in › blog › python › is a string mutable in python? let’s have a look at the concept
Is a String Mutable in Python? Let’s Have a Look
What’s the difference between modifying a string and reassigning a variable?
Modifying a string tries to change the original (not allowed). Reassigning a variable simply makes it point to a new string, leaving the original untouched.
guvi.in
guvi.in › blog › python › is a string mutable in python? let’s have a look at the concept
Is a String Mutable in Python? Let’s Have a Look
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'
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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.
GUVI
guvi.in › blog › python › is a string mutable in python? let’s have a look at the concept
Is a String Mutable in Python? Let’s Have a Look
February 3, 2026 - Strings in Python are immutable, which means you can’t change them directly—any modification creates a new string while the original stays the same.
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.
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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]
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In Python mutable sequence type is bytearray see this link
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This will allow you to efficiently change characters in a string. Although you can't change the string length.
>>> import ctypes
>>> a = 'abcdefghijklmn'
>>> mutable = ctypes.create_string_buffer(a)
>>> mutable[5:10] = ''.join( reversed(list(mutable[5:10].upper())) )
>>> a = mutable.value
>>> print `a, type(a)`
('abcdeJIHGFklmn', <type 'str'>)
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 )?
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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.
Real Python
realpython.com › python-mutable-vs-immutable-types
Python's Mutable vs Immutable Types: What's the Difference? – Real Python
January 26, 2025 - Python lists are mutable, allowing you to change, add, or remove elements. Strings in Python are immutable, meaning you can’t change their content after creation. To check if an object is mutable, you can try altering its contents.
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. Any operation that appears to modify a string actually creates a new string object.
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 - If you are already familiar with the concept of immutability, you can skip this section. Immutable objects cannot be modified and mutable objects can be modified. It is as simple as that.
Physics Forums
physicsforums.com › other sciences › programming and computer science
Are Python strings truly immutable? • Physics Forums
September 23, 2022 - There is no conceptual difference between the int code and string code above. At the level of Python functionality (which I distinguish from Python interpreter implementation) strings are mutable.
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). This avoids unnecessary bugs. Some other immutable objects are integer, float, tuple, and bool.
AmbitionBox
ambitionbox.com › home › interviews › interview questions
Is a string mutable or immutable in Python? (Asked in 4 companies) - AmbitionBox
Strings in Python are immutable. Once a string object is created, its contents (individual characters) cannot be changed — operations like concatenation, slicing or calling string methods return new string obje...read more
Great Learning
mygreatlearning.com › blog › it/software development › understanding mutable and immutable in python
Understand What is Mutable and Immutable in Python
October 14, 2024 - This is because they support the same sequence operations as strings. We all know that strings are immutable. The index operator will select an element from a tuple just like in a string.
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.
Medium
medium.com › better-programming › pointers-strings-and-im-mutability-680b15dd4a70
Pointers, Strings, and (im)mutability in Python | by Danny D. Leybzon | Better Programming
June 19, 2022 - Wrong! Any Python aficionado will tell you that Python strings are “immutable”, meaning that they can’t be modified directly. Instead, when you try to modify a string, Python will create a new object in memory based on the mutation that ...
Runestone Academy
runestone.academy › ns › books › published › fopp › TransformingSequences › Mutability.html
9.2. Mutability — Foundations of Python Programming
For example, in the following code, we would like to change the first letter of greeting. Instead of producing the output Jello, world!, this code produces the runtime error TypeError: 'str' object does not support item assignment. Strings are immutable, which means you cannot change an existing ...
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Strings don't have any methods on them that allow a change to the value of the string. In other words: strings are immutable.
When you call str.replace a new string is built and returned.
>>> s1 = 'Rohit'
>>> s2 = s1.replace('R', 'M')
>>>
>>> s1
'Rohit'
>>> s2
'Mohit'
As you can see s1 still has its original value.
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Strings are known as Immutable in Python (and other languages) because once the initial string is created, none of the function/methods that act on it change it directly, they simply return new strings.
So, in your example
str1='Rohit'
str1.replace('R','M')
After the .replace call, you should try evaluating str1 in your REPL. It might surprise you to see that str1 still holds the value 'Rohit'. The .replace returns a new string in which all instances of the given character are replaced with the specified character. Your REPL will print that returned string, but after that it is lost since you didn't assign it to anything.
Your second example is much the same, but with a string constant instead of a variable like str1.
Medium
medium.com › @float_and_confused › but-i-did-change-the-string-1ea3bab972db
Mutable vs Immutable in Python: Beginner’s Guide | Medium
June 16, 2025 - In C++, string is mutable. You can change individual characters directly using []. ... Python strings are immutable, so you can’t change part of the string.