Simplification of if multiple conditions in python

Question

I want to pick out some items in one rectangular box with axis limits of (xmin, xmax, ymin, ymax, zmin, zmax). So i use the following conditions,

if not ((xi >= xmin and xi <= xmax) and (yi >= ymin and yi <= ymax) and (zi >= zmin and zi <= zmax)):
    expression

But I think python has some concise way to express it. Does anyone can tell me?

Jean-François Fabre · Accepted Answer · 2018-12-12T21:27:31.497

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Typical case for operator chaining:

if not (xmin <= xi <= xmax and ymin <= yi <= ymax and zmin <= zi <= zmax):

Not only it simplifies the comparisons, allowing to remove parentheses, while retaining readability, but also the center argument is only evaluated once , which is particularly interesting when comparing against the result of a function:

if xmin <= func(z) <= xmax:

(so it's not equivalent to 2 comparisons if func has a side effect)

edited Dec 12 '18 at 21:27

answered Dec 12 '18 at 21:22

Jean-François Fabre

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[Associated documentation here](https://docs.python.org/3/reference/expressions.html#comparisons) – Maximilian Burszley Dec 12 '18 at 21:24
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@Gao If their answer satisfies your question, please mark it as such with the green checkmark. – Maximilian Burszley Dec 12 '18 at 21:24
@TheIncorrigible1 thanks. Was trying to get an internal bookmark on that page :) – Jean-François Fabre Dec 12 '18 at 21:25
Just wondering how that is valid. `xmin <= xi` returns True, which is evaluated as `1` and then it shouldn't make sense, but surprisingly, it works perfectly fine – Aykhan Hagverdili Dec 12 '18 at 21:26
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@Ayxan Comparison operators don't associate in this case; `x <= y <= z` is evaluated like `x <= y and y <= z` (but with `y` evaluated only once). It doesn't simply evaluate `x <= y` and then compare the result to `z`. – chepner Dec 12 '18 at 21:28
@chepner that's really interesting. Thanks for the clarification. – Aykhan Hagverdili Dec 12 '18 at 21:33
if you do `(x <= y) <= z`, then you get your nasty boolean effect you were (?) looking for – Jean-François Fabre Dec 12 '18 at 22:36

score 1 · Answer 2 · answered Dec 12 '18 at 21:56

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If you really want to start cooking with gas, create a class library for handling 3D points (e.g. by extending this one to include the Z coordinate: Making a Point Class in Python).

You could then encapsulate the above solution into a method of the class, as:

def isInBox(self, p1, p2):
    return (p1.X <= self.X <= p2.X and p1.Y <= self.Y <= p2.Y and p1.Z <= self.Z <= p2.Z)

answered Dec 12 '18 at 21:56

AltShift

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Yes. I understand your idea. Thanks. – Gao Dec 13 '18 at 22:29

Simplification of if multiple conditions in python

2 Answers2