Docs: improve equivalence expression for chained comparison #22589
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Add grouping parenthesis around the equivalence expression to make it clear that it is evaluated as a single expression.
`x < y < z` parses as a single expression, so while it is equivalent to x < y and y < z in isolation, it is different when used in an expression with `not`.
`not` has a higher precedence than `and`. We don't see this with `or` as it has a lower precedence than `and`. (See the next section on Boolean Expressions)
+ `not x < y < z` == `not (x < y < z)`
+ `not x < y and y < z` != `not (x < y and y < z)`
```
>>> import ast
>>> ast.dump(ast.parse('not x<y<z')) == ast.dump(ast.parse('not(x < y <z)'))
True
>>> ast.dump(ast.parse('not x < y and y < z')) == ast.dump(ast.parse('(not x < y) and y < z'))
True
>>> ast.dump(ast.parse('not x < y and y < z')) == ast.dump(ast.parse('not (x < y and y < z)'))
False
```
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This PR is stale because it has been open for 30 days with no activity. |
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Its usual to have an issue opened in https://bugs.python.org/
I suggest just copying the text from you conversation.
For documentation changes, we can generally skip an issue and news file. I've added the appropriate labels. 👍 |
Sure, however we don't have Thanks for the PR, but I'm not sure the addition necessarily helps with clarity in this case. |
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Thanks, but +1 to hugovk here |
Add grouping parenthesis around the informal equivalence expression to make it clear that it is evaluated as a single expression.
x < y < zparses as a single expression, so while it is equivalent to x < y and y < z in isolation, it is different when used in an expression withnot.nothas a higher precedence thanand. We don't see this withoras it has a lower precedence thanand. (See the next section on Boolean Expressions)not x < y < z==not (x < y < z)not x < y and y < z!=not (x < y and y < z)