The Illusion of Python String Mutability: A " " B

Python strings are widely known for their immutability. However, the code example you provided, involving a " " b, raises questions about this fundamental property. Let's dive into the explanation behind this seemingly contradictory behavior.

The Variable's Tale

When we assign a string to a variable, such as a = "Dog", it simply creates a reference to that string in memory. The variable does not own or hold a copy of the string itself; rather, it points to it. This is the essence of string immutability in Python.

The New Object Magic

In the code you mentioned, when you write a " " b, you're not modifying the strings pointed to by a or b. Instead, you're creating a new string that is the concatenation of both strings. This newly created string is then assigned to a new reference, leaving the original strings untouched.

Variable Reassignment

The crucial point here is the subsequent line of code:

a = a   " "   b   " "   c

This line is not modifying the string that a previously pointed to, but rather reassigning a to point at the new string you just created. Hence, now a points to the concatenated string "Dog eats treats," while the original "Dog" string remains unchanged.

Conclusion

While it may seem like the string "Dog" is being mutated, in reality, Python is creating and assigning new strings throughout the process. The immutability of strings remains intact, ensuring that once a string is created, its content cannot be altered.