


Combining the in and == operators in Python: an unexpected feature
Oct 15, 2025 pm 02:24 PMThis article aims to explain the confusing behavior that occurs when the `in` and `==` operators are used together in Python. By analyzing the principles behind it, we will reveal the characteristics of Python's comparison operator chain, and demonstrate through examples how this characteristic affects the execution results of the code, helping readers avoid potential errors and gain a deeper understanding of Python's operator precedence and associativity.
In Python, the expression "w" in "w" == "w" evaluates to True, which may seem counterintuitive at first. Many people may think that this expression will cause an error or return False due to operator precedence issues. But in fact, Python handles the chained use of multiple comparison operators in a special way.
chain of comparison operators
Python's documentation clearly states that comparison operators can be chained together arbitrarily. For example, x
Therefore, the expression "w" in "w" == "w" is actually equivalent to "w" in "w" and "w" == "w". Let’s break it down:
- "w" in "w" evaluates to True because the string "w" does contain the character "w".
- "w" == "w" also evaluates to True because the two strings are equal.
- Therefore, the entire expression becomes True and True, and the final result is True.
Sample code
To better understand this feature, we can look at some other examples:
print("a" in "abc" == "abc") # Output True, equivalent to "a" in "abc" and "abc" == "abc" print(1 2 == 2) # Output False, equivalent to 1 > 2 and 2 == 2
Notes and Summary
It is very important to understand the chaining feature of Python's comparison operators. It can help us write more concise code, but it may also lead to some unexpected results. When using multiple comparison operators, be sure to understand how they are combined and the order of evaluation in Python.
- Avoid overuse of chained comparisons: Although chained comparisons can simplify your code, in some cases it may be clearer and easier to understand using the and and or operators explicitly.
- Pay attention to operator precedence: Although comparison operators can be chained, you still need to pay attention to operator precedence to ensure that expressions evaluate as expected.
- Test and verify: For complex expressions, it's a good idea to test and verify to make sure the code behaves as expected.
All in all, Python's comparison operator chaining feature is a powerful and flexible tool, but it needs to be used with caution and a full understanding of how it works to avoid potential errors and write more robust and maintainable code. Through the explanations and examples in this article, I hope to help readers have a deeper understanding of this feature of Python and use it flexibly in actual programming.
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