Why Do Python Strings Appear Mutable When Using \"a \" \" b\"?

Unveiling the Mutable Nature of Python Strings: An Exploration of a " " b

Despite the long-held belief that Python strings are inherently immutable, a peculiar observation challenges this notion. When concatenating strings using the a " " b syntax, strings appear to undergo alterations. Let's investigate this puzzling behavior.

Investigating the Code

Consider the following code snippet:

<code class="python">a = "Dog"
b = "eats"
c = "treats"

print a, b, c
# Dog eats treats

print a + " " + b + " " + c
# Dog eats treats

print a
# Dog

a = a + " " + b + " " + c
print a
# Dog eats treats
# !!!</code>

Understanding the Anomaly

As per our understanding, Python strings are immutable, prohibiting direct manipulation of their contents. However, the code above demonstrates otherwise. Upon executing the line a = a " " b " " c, the string pointed to by a appears to have been modified, leading to confusion.

Unraveling the Mystery

Here lies the key to understanding this behavior: Python strings themselves remain immutable. Instead, the variable a is reassigned to a new string object containing the concatenated contents.

In the first part of the code, a initially points to the string "Dog". When we concatenate strings using a " " b, a new string is created in memory that contains the result of the concatenation, in this case, "Dog eats treats". However, a still points to the original "Dog" string.

When we assign the value a " " b " " c to a, this creates a new string object that contains the concatenated result, "Dog eats treats", and a now points to this new string. The original "Dog" string remains unchanged and is still accessible in memory.

Therefore, the apparent mutation of strings in this context is a result of reassignment of the variable pointing to the string, not a modification of the string itself. Python strings uphold their immutable nature while providing the flexibility to alter the references pointing to them.

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