What Does Python's `id()` Function Really Tell You?

Delving into Python's id() Function: Its Purpose and Usage

The id() function within Python sparks curiosity with its enigmatic behavior. It returns an immutable integer (or long integer) that symbolizes an object's unique identity throughout its existence. Interestingly, this value doesn't directly align with the object's size or its memory address in C.

Unveiling the Meaning of the Returned Integer

Unlike typical integers representing quantities, the output of id() is a constant identifier specific to each object. It resembles a fingerprint that eternally distinguishes that particular object.

Is id() Equivalent to Memory Addresses in C?

While the id() function's output is similar to memory addresses in C, the two are not directly connected. In certain Python implementations, such as CPython, the returned integer does equate to the memory address of the underlying C object. However, this connection isn't inherent to all Python implementations.

Why the Integer Doesn't Match Object Size

The discrepancy between the returned integer and an object's size stems from the way Python handles lists. A list in Python acts as a container for references to its elements rather than storing the elements themselves. As such, the id() call on a list element returns the identity of the reference, not the size of the object it refers to.

Practical Applications of id()

The id() function, though rarely used, has valuable applications in debugging. It enables developers to verify if two references point to the same object in memory. Comparing object identities via id() can identify programming errors and unexpected behavior.

Overall, the id() function in Python provides a unique and consistent identifier for objects. It's a valuable tool for debugging but is not commonly used in typical programming scenarios.

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