Why Does `0 < 0 == 0` Return False in Python?

The Puzzling Expression: Why Does 0 < 0 == 0 Return False in Python?

Python's queuing mechanism in Queue.py presents an intriguing expression that evaluates to False: 0 < 0 == 0. Understanding this behavior requires unraveling Python's interpretation of chained comparisons.

Chained Comparisons: A Simplified Approach

Python simplifies range comparisons by allowing for chained relational operators. Instead of writing (0 < x) and (x <= 5), one can concisely use 0 < x <= 5. This convenience underlies the behavior of 0 < 0 == 0.

Step-by-Step Interpretation of Chained Comparison

When encountering a chained comparison, Python operates sequentially:

1. Evaluate the leftmost relation (0 < 0). This returns True.
2. Compare the result to the middle value (the right-hand side of the second relation). This checks True == 0, which evaluates to False.

Why the Parenthesized Expressions Return True

Introducing parentheses alters the evaluation order, affecting the interpretation:

• (0 < 0) == 0: The first comparison True is then checked against 0, resulting in True.
• 0 < (0 == 0): Here, 0 is compared to False, yielding True.

Conclusion

Python's handling of chained comparisons simplifies range comparisons. However, their interpretation requires understanding the sequential comparison process. The expression 0 < 0 == 0 evaluates to False because the chained comparisons are evaluated left to right, not parenthetically. Parentheses can force a different evaluation order, leading to different results.

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