8 ms·

Not the parent but := assignment expressions and match expressions are abominations.

asah 5y ago
Disagree: the recent changes are things I put to work immediately and in a large fraction of the code. They're not niche and "should have" been added years ago. If anything, I'm thrilled with the work of the "committee," whose judgments are better than the result of any individual. Postgres is the same. Gone are the days when you invest in a platform like python, and they make crazy decisions that kill the platform's future (e.g. perl5). Ignore small syntax stuff like := and focus on the big stuff.
- dataflow 5y ago
  > Disagree: the recent changes are things I put to work immediately and in a large fraction of the code. That says nothing about their quality. It just says you like them. If you gave me unhealthy food I'd probably eat it immediately too. Doesn't mean I think it's good for me. > Ignore small syntax stuff like := and focus on the big stuff. They're not "small" when you immediately start using them in a "large fraction of your code". And a simple syntax that's easy to understand is practically Python's raison d'être. They added constructs with some pretty darn unexpected meanings into what was supposed to be an accessible language, and you want people to ignore them? I would ignore them in a language like C++ (heck, I would ignore syntax complications in C++ to a large degree), but ignoring features that make Python harder to read? To me that's like putting performance-killing features in C++ and asking people to ignore them. It's not that I can't ignore them—it's that that's not the point.
  - DangitBobby 5y ago
    I simply do not understand how the walrus operator is harder to read. Maybe an example? my_match = regex.match(foo) if my_match: return my_match.groups() # continues with the now useless my_match in scope Versus if my_match := regex.match(foo): return my_match.groups() # continues without useless my_match in scope How is the second one less readable? Have you ever heard of a real world example of a beginner or literally anyone ever actually expressing confusion over this?
    - dataflow 5y ago
      The problem isn't that simple use case. Although even in that case, they already had '=' as an assignment operator, and they could've easily kept it like the majority of other languages do instead of introducing an inconsistency. The more major problem with the walrus operator is more complicated expressions they made legal with it. Like, could you explain to me why making these legal was a good thing? def foo() return ... def bar(): yield ... while foo() or (w := bar()) < 10: # w is in-scope here, but possibly nonexistent! # Even in C++ it would at least *exist*! print(w) # The variable is still in-scope here, and still *nonexistent* # Ditto as above, but even worse outside the loop print(w := w + 1) If they just wanted your use case, they could've made only expressions of the form 'if var := val' legal, and maybe the same with 'while', not full-blown assignments in arbitrary expressions, which they had (very wisely) prohibited for decades for the sake of readability. And they would've scoped the variable to the 'if', not made it accessible after the conditional. But nope, they went ahead and just did what '=' does in any language, and to add insult to injury, they didn't even keep the existing syntax when it has exactly the same meaning. And it's not like they even added += and -= and all those along with it (or +:= and -:= because apparently that's their taste) to make it more useful in that direction, if they really felt in-expression assignments were useful, so it's not like you get those benefits either.
      - DangitBobby 5y ago
        In your example, if you leave out the parentheses around w := bar(), you get "SyntaxError: cannot use assignment expressions with operator" which makes me think it's a bug in the interpreter and not intentionally designed to allow it. I am baffled to learn that it's kept in scope outside of the statement it's assigned, and I agree it would have a negative impact on readability if used outside of the if statement.
        dataflow 5y ago
        > if you leave out the parentheses around w := bar(), you get "SyntaxError: cannot use assignment expressions with operator" which makes me think it's a bug in the interpreter and not intentionally designed to allow it. No, I'm pretty sure that's intentional. You want the left-hand side of an assignment to be crystal clear, which "foo() or w := bar()" is not. It looks like it's assigning to (foo() or w).
DangitBobby 5y ago
I have now heard specific concerns with := that make sense to me, but what about match expressions? What about them do you not like?
- dataflow 5y ago
  What's the output of this program? class C(object): A = 1 B = 2 x = 3 y = 10 print(x - B) match y: case C.A: print('A') case B: print(y - B)
  - DangitBobby 5y ago
    Do you not like the idea of pattern matching as a feature or do you not like the implementation details? This kind of seems like another clumsy scoping problem, no?
    - dataflow 5y ago
      I would love a good pattern matching feature, but this is not it. And this is a seriously broken design at a fundamental level, not an "implementation detail". I actually have no clue how it's implemented and couldn't care less honestly. I just know it's incredibly dangerous for the user to actually use, and incredibly unintuitive on its face. It's as front-and-center as a design decision could possibly be, I think. And no, this is not really a scoping issue. Match is literally writing to a variable in one pattern but not the other. A conditional write is just a plain inconsistency. The sad part is both of these features are stumbling over the fact that Python doesn't have variable declarations/initialization. If they'd only introduced a different syntax for initializations, both of these could have been much clearer.
      - DangitBobby 5y ago
        > I actually have no clue how it's implemented and couldn't care less honestly. I guess I'm not sure where "design" ends and "implementation" begins? To me, how to handle matching on variables that already exists is both, because "pattern matching and destructuring" are the features and how that must work in the context of the actual language is "implementation". It being written in a design doc and having real world consequences in the resulting code doesn't make it not part of the implementation. Instead of quibbling over terms, I was much more interested in whether you like the idea of pattern matching. I think not liking the final form a feature takes in the language is fundamentally different from wholesale disliking the direction the language design is going.
DangitBobby 5y ago
I'll point out that the walrus operator was actually accepted while Guido was still BDFL (and the vitriol surrounding the decision to include it led directly to him stepping down from the position [1]), so even accepting the fact that it's a poor addition to the language, does not provide support for the statement that "design by committee" has lead to poor language design decisions. 1. https://pythonsimplified.com/the-most-controversial-python-walrus-operator/ https://pythonsimplified.com/the-most-controversial-python-w...
- dataflow 5y ago
  You'll want to post that as a reply to the parent you originally replied to, since I'm not the one who said anything about design-by-committee.
  - DangitBobby 5y ago
    They gave no specific criticisms. This thread was born of a request for specific criticisms. When that happens, I try to operate as though the assumptions laid out in the parents hold for the children. I think this makes sense to do, especially when you appeared to step in as a proxy expanding on the parent's opinion. Even if that wasn't your intention, this is a public thread, and the most relevant place to post things as a response to a sentiment in a thread may not be directly to a person who holds that exact sentiment. If you don't take issue with "design by committee" then you need not be concerned. I don't think you think that, and I think no less of you regardless.
    - dataflow 5y ago
      I meant it moreso that the person whom the reply is actually relevant to might not see it otherwise, but whatever, it's fine with me.

asah 5y ago

Disagree: the recent changes are things I put to work immediately and in a large fraction of the code. They're not niche and "should have" been added years ago. If anything, I'm thrilled with the work of the "committee," whose judgments are better than the result of any individual. Postgres is the same. Gone are the days when you invest in a platform like python, and they make crazy decisions that kill the platform's future (e.g. perl5). Ignore small syntax stuff like := and focus on the big stuff.

dataflow 5y ago
> Disagree: the recent changes are things I put to work immediately and in a large fraction of the code. That says nothing about their quality. It just says you like them. If you gave me unhealthy food I'd probably eat it immediately too. Doesn't mean I think it's good for me. > Ignore small syntax stuff like := and focus on the big stuff. They're not "small" when you immediately start using them in a "large fraction of your code". And a simple syntax that's easy to understand is practically Python's raison d'être. They added constructs with some pretty darn unexpected meanings into what was supposed to be an accessible language, and you want people to ignore them? I would ignore them in a language like C++ (heck, I would ignore syntax complications in C++ to a large degree), but ignoring features that make Python harder to read? To me that's like putting performance-killing features in C++ and asking people to ignore them. It's not that I can't ignore them—it's that that's not the point.
- DangitBobby 5y ago
  I simply do not understand how the walrus operator is harder to read. Maybe an example? my_match = regex.match(foo) if my_match: return my_match.groups() # continues with the now useless my_match in scope Versus if my_match := regex.match(foo): return my_match.groups() # continues without useless my_match in scope How is the second one less readable? Have you ever heard of a real world example of a beginner or literally anyone ever actually expressing confusion over this?
  - dataflow 5y ago
    The problem isn't that simple use case. Although even in that case, they already had '=' as an assignment operator, and they could've easily kept it like the majority of other languages do instead of introducing an inconsistency. The more major problem with the walrus operator is more complicated expressions they made legal with it. Like, could you explain to me why making these legal was a good thing? def foo() return ... def bar(): yield ... while foo() or (w := bar()) < 10: # w is in-scope here, but possibly nonexistent! # Even in C++ it would at least *exist*! print(w) # The variable is still in-scope here, and still *nonexistent* # Ditto as above, but even worse outside the loop print(w := w + 1) If they just wanted your use case, they could've made only expressions of the form 'if var := val' legal, and maybe the same with 'while', not full-blown assignments in arbitrary expressions, which they had (very wisely) prohibited for decades for the sake of readability. And they would've scoped the variable to the 'if', not made it accessible after the conditional. But nope, they went ahead and just did what '=' does in any language, and to add insult to injury, they didn't even keep the existing syntax when it has exactly the same meaning. And it's not like they even added += and -= and all those along with it (or +:= and -:= because apparently that's their taste) to make it more useful in that direction, if they really felt in-expression assignments were useful, so it's not like you get those benefits either.
    - DangitBobby 5y ago
      In your example, if you leave out the parentheses around w := bar(), you get "SyntaxError: cannot use assignment expressions with operator" which makes me think it's a bug in the interpreter and not intentionally designed to allow it. I am baffled to learn that it's kept in scope outside of the statement it's assigned, and I agree it would have a negative impact on readability if used outside of the if statement.
      - dataflow 5y ago
        > if you leave out the parentheses around w := bar(), you get "SyntaxError: cannot use assignment expressions with operator" which makes me think it's a bug in the interpreter and not intentionally designed to allow it. No, I'm pretty sure that's intentional. You want the left-hand side of an assignment to be crystal clear, which "foo() or w := bar()" is not. It looks like it's assigning to (foo() or w).

DangitBobby 5y ago

I have now heard specific concerns with := that make sense to me, but what about match expressions? What about them do you not like?

dataflow 5y ago
What's the output of this program? class C(object): A = 1 B = 2 x = 3 y = 10 print(x - B) match y: case C.A: print('A') case B: print(y - B)
- DangitBobby 5y ago
  Do you not like the idea of pattern matching as a feature or do you not like the implementation details? This kind of seems like another clumsy scoping problem, no?
  - dataflow 5y ago
    I would love a good pattern matching feature, but this is not it. And this is a seriously broken design at a fundamental level, not an "implementation detail". I actually have no clue how it's implemented and couldn't care less honestly. I just know it's incredibly dangerous for the user to actually use, and incredibly unintuitive on its face. It's as front-and-center as a design decision could possibly be, I think. And no, this is not really a scoping issue. Match is literally writing to a variable in one pattern but not the other. A conditional write is just a plain inconsistency. The sad part is both of these features are stumbling over the fact that Python doesn't have variable declarations/initialization. If they'd only introduced a different syntax for initializations, both of these could have been much clearer.
    - DangitBobby 5y ago
      > I actually have no clue how it's implemented and couldn't care less honestly. I guess I'm not sure where "design" ends and "implementation" begins? To me, how to handle matching on variables that already exists is both, because "pattern matching and destructuring" are the features and how that must work in the context of the actual language is "implementation". It being written in a design doc and having real world consequences in the resulting code doesn't make it not part of the implementation. Instead of quibbling over terms, I was much more interested in whether you like the idea of pattern matching. I think not liking the final form a feature takes in the language is fundamentally different from wholesale disliking the direction the language design is going.

DangitBobby 5y ago

I'll point out that the walrus operator was actually accepted while Guido was still BDFL (and the vitriol surrounding the decision to include it led directly to him stepping down from the position [1]), so even accepting the fact that it's a poor addition to the language, does not provide support for the statement that "design by committee" has lead to poor language design decisions. 1. https://pythonsimplified.com/the-most-controversial-python-walrus-operator/ https://pythonsimplified.com/the-most-controversial-python-w...

dataflow 5y ago
You'll want to post that as a reply to the parent you originally replied to, since I'm not the one who said anything about design-by-committee.
- DangitBobby 5y ago
  They gave no specific criticisms. This thread was born of a request for specific criticisms. When that happens, I try to operate as though the assumptions laid out in the parents hold for the children. I think this makes sense to do, especially when you appeared to step in as a proxy expanding on the parent's opinion. Even if that wasn't your intention, this is a public thread, and the most relevant place to post things as a response to a sentiment in a thread may not be directly to a person who holds that exact sentiment. If you don't take issue with "design by committee" then you need not be concerned. I don't think you think that, and I think no less of you regardless.
  - dataflow 5y ago
    I meant it moreso that the person whom the reply is actually relevant to might not see it otherwise, but whatever, it's fine with me.