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Why does `(1 in [1,0] == True)` evaluate to `False` in Python?

Patricia Arquette
Patricia ArquetteOriginal
2024-11-01 04:23:021018browse

Why does `(1 in [1,0] == True)` evaluate to `False` in Python?

False Evaluation of (1 in [1,0] == True)

Unlike a typical programming language, Python evaluates expressions using comparison operator chaining. In the expression (1 in [1,0] == True), the operation is not parsed as expected.

The expression is actually interpreted as:

(1 in [1, 0]) and ([1, 0] == True)

This evaluation breaks down into:

  • (1 in [1, 0]): This evaluates to True because 1 is present in the list [1, 0].
  • ([1, 0] == True): This evaluates to False because [1, 0] is a list, not a boolean value.

The overall expression, therefore, evaluates to:

True and False = False

This unexpected result highlights the difference in Python's evaluation of expressions compared to other languages. To avoid confusion, use parentheses to specify the desired evaluation order:

(1 in [1,0]) == True # True

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