Some people find this legal syntax confusing: A in B < C
(It means A in B and B < C.) I feel like most code reviews would not allow this kind of code to be checked in, at least without a comment explaining what the code does. What are the motivating reasons for allowing this syntax? Is there any idiomatic code that uses it? If not, I suggest dividing the comparison operators into two groups: in, not in, is, is not and <, >, <=, >=, ==, != and then disallowing chaining of operators from both groups. For example, still allowed: A <= B <= C A in B in C disallowed: A < B in C The advantage of such a change is that there is fewer "gotcha" code. I admit that this code is rarely written, but it can come up. For example, you might write your own comparison operator and then want to see if it's working: A < B is None returns false if B is not None even if A < B returns None. Also, in my opinion, the existence is a deterrent to Python and takes away from Python's beauty as a language. The downside of such a change is that the language is more complicated. As far as implementation goes, this can be done after parsing when the AST is checked and errors are raised (from what I remember). Best, Neil
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