Python's `==` vs. `is`: When Do They Produce Different Results for Identical Objects?

Instance Identity and Object Comparison in Python: Understanding == and is

In Python, two string variables can be assigned identical values, yet produce different results when compared using '==' and 'is' operators. This discrepancy arises from the concept of instance identity versus object equality.

'==' evaluates object equality, determining whether two variables refer to the same object in memory. In contrast, 'is' performs identity testing and checks if two variables point to the exact same instance of an object.

To illustrate:

s1 = 'text'
s2 = 'text'

In this case, both s1 and s2 refer to the same string object in memory. As such, '==' will return True as they have identical values.

However, if we create another string 'text' by concatenating characters:

s3 = ''.join(['t', 'e', 'x', 't'])

Although s3 has the same value as s1 and s2, it is a distinct object in memory. Hence, 'is' will return False as they are not the same instance.

In summary, '==' tests for object equality, while 'is' checks for instance identity. Understanding this distinction is crucial for accurate comparison of Python objects.

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