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Asked: 2024-09-26T20:11:26+05:30 In:

Is using ((a > b) – (a < b)) the best way to mimic cmp in Python 3?

I recently stumbled upon this neat little trick involving comparison operators in Python that got me thinking about the different ways we can optimize our code, and I wanted to discuss it with you all. So, there’s this function called `cmp` in Python 2, which let us compare two values and return -1, 0, or 1 based on their relationship. It’s not available in Python 3, and I heard that there’s a way to simulate its behavior using a combination of operators like `-`, `<`, `>`, etc.

Here’s the deal: I’ve tried implementing a custom `cmp` function using standard operators. While it feels like a fun challenge, the syntax can get a little messy. The gist is to leverage the comparison operators to return the same -1, 0, or 1 that `cmp` would. For example, if I compare `a` and `b`, I want a return of -1 if `a < b`, 0 if they're equal, and 1 if `a > b`.

I came across a really compact solution where they were using `((a > b) – (a < b))`, which is super clever but also a bit harder to grasp at first sight. I appreciate the elegance of reducing code, but it had me scratching my head for a bit. So, here's my question: is this the most efficient way to mimic `cmp` in Python 3? Or is there an even shorter or neater trick I've overlooked? Also, what are your thoughts on this approach? Do you think it compromises readability for the sake of brevity? I'm really looking to understand the balance between clean, readable code and the point of golfing it down. Plus, I’m curious if anyone here has stumbled upon this or tried other methods that achieve similar results. Would love to hear your thoughts, tips, or even wild one-liners that you might have up your sleeve!

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    2 Answers

    1. Custom cmp Function in Python 3

      Hey there! I totally get where you’re coming from with trying to recreate the behavior of the cmp function from Python 2 in Python 3. It’s a neat little exercise!

      Your idea of using ((a > b) - (a < b)) is indeed a clever one! Here's how it works:

      • If a < b, then (a > b) is False (0) and (a < b) is True (1), so it returns -1.
      • If a == b, both comparisons return False, so you get 0.
      • If a > b, then (a > b) is True (1) and (a < b) is False (0), yielding 1.

      Here's a simple implementation:

      def custom_cmp(a, b):
    return (a > b) - (a < b)

      Now, is this the most efficient way? While it's pretty compact, it's also vital to think about readability. A lot of people (especially beginners!) might find it a bit tricky at first glance. You could also use a classic if-elif-else structure:

      def custom_cmp(a, b):
    if a < b:
        return -1
    elif a > b:
        return 1
    else:
        return 0

      This version is much clearer for someone who’s just starting out, even if it takes a bit more space. You have to balance between writing less code and making it understandable.

      If you’re interested in some Pythonic ways to compare values, consider using the built-in functools.cmp_to_key function, which provides a more formal structure for such comparisons.

      In the end, it's all about what makes the most sense for you and your team. Do you want to impress with brevity, or prioritize clarity? I think both approaches have their merits, depending on the context and audience!

      Hope this helps you think through the problem! Happy coding!

    2. The use of comparison operators to simulate the behavior of the now-absent `cmp` function from Python 2 is indeed an interesting approach in Python 3. The expression you mentioned, `((a > b) – (a < b))`, efficiently returns -1, 0, or 1 depending on the relationship between `a` and `b`. This compact solution leverages Boolean arithmetic, where `True` is treated as 1 and `False` as 0. While this solution is mathematically efficient and clever, it can indeed compromise readability for those who are not familiar with such techniques. The balance between concise code and readability is a crucial aspect of programming style, where often, clearer but slightly longer code is preferred in collaborative environments to ensure that all developers can easily understand the logic being implemented.

      While the approach using `((a > b) – (a < b))` is effective, another way to define a `cmp`-like function could be to use Python's `functools.cmp_to_key()` in cases where you need to use it for sorting. However, if brevity is the goal, the one-liner you mentioned is indeed quite performant. Still, it’s beneficial to comment on such compact code to enhance readability. Ultimately, it's about choosing the right tool for the job—if the code is part of a larger project or will be maintained by others, consider using a more explicit approach, even if it means sacrificing a bit of brevity. Engaging with your fellow developers regarding their preferences for readability vs. brevity could also yield valuable insights into coding standards in your environment.

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