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Python FTW: Under the Hood

How Not to Use the "is" Operator

Explore how the Python is operator works compared to the == operator by examining object identity versus value equality. Learn when and why Python optimizes object allocation, understand version-specific behavior, and avoid pitfalls when using is with integers and other data types.

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Let’s learn how to correctly use the is operator in Python.

1.

Can you explain the behavior in the code below?

Python 3.5
>>> a = 256
>>> b = 256
>>> a is b
True        # output
>>> a = 257
>>> b = 257
>>> a is b
False       # output

Try it out in the terminal below:

Terminal 1
Terminal
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2.

Let's try a similar thing with data structures.
Python 3.5
a = []
b = []
print(a is b)
a = tuple()
b = tuple()
print(a is b)

3.

Let’s observe the behavior in Python 3.8 versus Python 3.7.

⚠️ The following code is meant for Python 3.8 specifically.

C++
# using Python 3.8
a, b = 257, 257
print(a is b)

⚠️ The following code is meant for Python 3.7 specifically.

C++
# using Python 3.7
a, b = 257, 257
print(a is b)

Explanation

The difference between is and == operators

  • The
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