Maybe be evil and add 1000 "Private access not allowed: {name}" with 1 second delays between each.
Aaaand, this flexibility is exactly why python is slow.
So, the question will come down to which causes more grief, people abusing this convention, or people that overly use the language features that combat it? It is the standard optimization question between poor practices and enforcement that you have in any question of enforcement.
I would be delighted if we could get some empirical data on this.
I wish you were right but, IMHE, it requires a lot of communication once teams grow and many team member do not fully understand the consequences of what they do. It is nice to have something that helps when reviewing code.
> If you have members that users probably shouldn't touch, you prepend them with an underscore
Well, this is precisely what TFA does. It prepends the constructor with an underscore.
> even if you keep all your fields private, the constructor is still, inherently, public.
ShippingOptions and the literals / enums are part of the public API, so the user would just be writing
ShippingOptions(Carrier.USPS, Conveyance.Air)
Dataclasses do have a `kw_only` option, but I'm not sure how well underscore prefixes would be understood as private parameters / a private ctor, whereas wrapping a clearly "private" type should be clear to everybody.
Glyph is not entirely correct on the "any class" bit as you can always break the default init path:
class ShippingOptions:
_ship: Literal["fast", "normal", "slow"]
__init__ = None
def shipFast() -> ShippingOptions:
opts = object.__new__(ShippingOptions)
opts._ship = "fast"
return opts
That PR might well be rejected. And you have to work with the module owners to get your case supported.
Anything else is not responsible and I would not call it "adult".
Like the rest of that circle, he moves with the times, supports public shaming of Tim Peters and others and now promotes poorly implemented information hiding so Python ticks a few more boxes for the industry.
Information hiding in a language that allows changing the values of small integers at runtime via ctypes is doomed anyway. And there are plenty of better languages that do it out of the box and in a straightforward manner.
Only then are you truly putting a solid boundary between your library and the folks using your library. Everything else is just praying that you and only you have an underscore on your keyboard! :)
And of course another alternative is to accept that there is no true private in Python other than defdef*, so you allow your ShippingOption to be publicly visible while also documenting that the helper-constructors are what should really be used.
*”defdef” as in function definitions inside other function definitions — closures if you will, although I prefer to write mine as taking most if not all their parameters explicitly:
def public(foo):
def private(foo):
…
class Private:
… # less common
…In practice, I found it difficult for coworkers to read and understand so I dropped the idea.
Another limitation I found is that it breaks down when you start using inheritance. For example:
```
class _A: pass
A = NewType("A", _A)
class _B(_A): pass
B = NewType("B", _B)
def foo(a: A) -> None: pass
b = B(_B())
foo(b) # Mypy is not happy: Argument 1 to "foo" has incompatible type "B"; expected "A"
foo(A(b)) # Mypy is OK
```
from typing import *
class _A:
pass
class _B(_A):
pass
A = NewType("A", _A)
B = NewType("B", _B)
def foo[T: (A, B)](val: T) -> T:
return val
a = A(_A())
b = B(_B())
_a = foo(a)
_b = foo(b)
reveal_type(_a)
reveal_type(_b)
OP could just do:
def foo(val: _A) -> None:
pass
It's sad to see that many features regarding object-oriented programming and static typing are implemented worse in Python than Java. Various examples: __str__() vs. toString(); underscore vs. private; @staticmethod/@classmethod vs. static; generic types are so clunky in Python; types are not shown in the official Python standand library documentation; __init__() doesn't force you to call super() whereas it's mandatory in Java; @override (Python 3.12; year 2023) copying Java @Override (JDK 1.5; year 2004) very late; convention changing from duck typing (always available in Python) to structural typing (optional in Python, mandatory in Java).
My real problem with the evolution of Python is that initially, the language and the community was positioned as anti-Java, anti-big-OOP-like-C++, and then it changed into the thing that it was against, but in a roundabout and suboptimal way. To me, the initial vibe of Python was, "write a 100-line script, don't worry about explicitly documenting types, don't worry about grand architecture, don't worry about creating custom classes, don't worry about encapsulation and public/private". I've been with Python since year 2007 in the 2.x days, and Java since 2002.
Initial examples: Why go through the ceremony of `public static void main(String[] args)` when Python just executes the script line by line at the top level? Oh wait, now you have things like `import` actually executing code instead of simply being a compile-time namespace convenience, and you need weird techniques like `if __name__ == "__main__"`. Why `System.out.println()` when `print()` is so much more concise? But now you're polluting the global namespace, and `print(file=sys.stderr)` isn't that elegant either.
Static typing in Python is the biggest hypocrisy ever. As I understood it, Python scripts were meant to be lightweight and free of the tyranny of enterprise OOP which was epitomized by Java. But people found out that keeping track of types in your head is laborious and error-prone, and getting a compiler to check {that the shape of your objects and function calls match} is a huge productivity boost. And so Python 3 enabled static type hints... which, like I said before, Java had from day zero. To make matters worse, static type hint features were introduced progressively over the years, leading to things getting deprecated from the `typing` module and moved to things like `T|None` and `list[T]` and `collections.abc`.
IIRC the old practice in Python was that you specified some kind of interface in prose or in code (e.g. `class IoStream: def read(); def close()`), but you didn't need to explicitly use that interface as a superclass; you can just duck-type your way around things. But this completely goes against static typing, so I'm pretty sure the new preferred way is to explicitly use abstract superclasses... just like Java did all along (and is mandatory).
I really don't think having top-level (module) variables and functions in Python is a good thing, especially because then they are duplicated as fields and methods in classes. In Java, fields and methods (whether static or instance) can only be placed in classes, and I think this particular straitjacket is a good thing.
> because Python wants these things to be optional
We can both agree that Python gives multiple ways to do things (e.g. no static type hints vs. static type hints). This flies in the face of:
> Readability counts.
> The Zen of Python / There should be one-- and preferably only one --obvious way to do it. -- https://peps.python.org/pep-0020/
Probably the most tragic example is the ways to build up strings in Python: `+` and str(), `%` operator, `str.format()`, f-string.
(To be fair, I have a laundry list of complaints about Java too, such as: .class files and the JVM being an intermediate layer that needs to be understood which is actually different from the Java source language, lack of in-place structs so `new Point[]` is very painful on the memory system, awkward string interpolation/formatting compared to Python's f-strings, very awkward JDBC compared to for example Python sqlite3 API, kinda clunky for web server programming, very awkward JSON handling, enterprisey libraries and APIs that are perfectly documented but are impossible to actually understand.)
typing.Protocol is a good fit for this use case
from typing import Protocol
class HasMessage(Protocol):
def get_message(self) -> str: ...
class A:
"""Implicit (duck-typed)"""
def get_message(self) -> str:
return "A"
class B(HasMessage):
"""Explicit"""
def get_message(self) -> str:
return "B"
class C:
def get_message(self) -> int:
return 1
def print_message(m: HasMessage) -> None:
print(m.get_message())
print_message(A())
print_message(B())
print_message(C()) # fails type checkhttps://peps.python.org/pep-0544/#explicitly-declaring-imple...
Yes, agreed. I used to work on a large python codebase and tried to add type hints where I could. The issue is that python was not the right tool for the job - except that switching to the right tool was a non-starter. So type hints were the best I could do.
I don't think this is a fair criticism. Python is a scripting language, it makes sense that the code is executed line by line at the top level. This is also how other programming languages from its time like Perl or Bash does it. Even newer scripting languages like Ruby does something similar.
> Why `System.out.println()` when `print()` is so much more concise? But now you're polluting the global namespace, and `print(file=sys.stderr)` isn't that elegant either.
Another criticism that I don't think it is fair. Lots of other languages "polutes" the global namespace. I actually can't think another language other than Java that doesn't. Python at least still allow you to manually `import builtins`, but Go for example AFAIK has no mechanism for you to reference builtins if you end up shadowing them.
Also I find `print(file=sys.stderr)` pretty much elegant, it works exactly how I would expect, it also means I can open a file and write to it using `print`.
> And so Python 3 enabled static type hints... which, like I said before, Java had from day zero.
Again, I don't think this is fair. I find Python 3 type-hints much more powerful than whatever type system Java has, especially because Python has Option types that actually make the type system useful (Java is infamous for its NullPointerException for a reason).
You'll note that even Java now recognises that "public static void main(String[] args)" was pointless ceremony.
> Python scripts were meant to be lightweight and free of the tyranny of enterprise OOP which was epitomized by Java. But people found out that keeping track of types in your head is laborious and error-prone, and getting a compiler to check {that the shape of your objects and function calls match} is a huge productivity boost. And so Python 3 enabled static type hints... which, like I said before, Java had from day zero.
Java didn't have "hints", it had mandatory types everywhere. Which, again, they've now recognised was a bad idea and gradually removed. Having a type system is a good idea, and maybe if Python had taken more inspiration from OCaml (or more people had used OCaml instead of either Java or Python) we'd all be better off, but the early-2000s-Java cure of mandatory types everywhere was worse than the disease.
> To make matters worse, static type hint features were introduced progressively over the years, leading to things getting deprecated from the `typing` module and moved to things like `T|None` and `list[T]` and `collections.abc`.
Which happens in any language that evolves over time. Java, despite having a type system built into the language from day 1, now has about ten different deprecated sets of nullness annotations with overlapping functionality.
> I really don't think having top-level (module) variables and functions in Python is a good thing, especially because then they are duplicated as fields and methods in classes. In Java, fields and methods (whether static or instance) can only be placed in classes, and I think this particular straitjacket is a good thing.
Nah. No other language has adopted Java's approach, for good reason. Functions and values are easier than classes and the language shouldn't force you to complicate your code when there's no need to.
> Probably the most tragic example is the ways to build up strings in Python: `+` and str(), `%` operator, `str.format()`, f-string.
It sucks, but what's the alternative? Either a language dies young or it lives long enough to have a bunch of deprecated crap in it.
There is still the part of the ceremony that actually mattered: having a single entrypoint instead of the option to litter side effects throughout the file and having those side effects execute automatically on import.
> It sucks, but what's the alternative?
3.0 was a big missed opportunity to kill a lot of the deprecated cruft.
You can actually do that in Java too with static initialisation blocks.
> 3.0 was a big missed opportunity to kill a lot of the deprecated cruft.
Maybe. 3.0 already came damn close to killing the language. If they'd made the changes any more radical it could easily have been another Perl 6.
It really wasn't that anti-Java. Late 90s / early 2000s had a huge branch that was very dedicated to Java-style OOP. E.g. anything to do with Zope, and GvR himself worked on that at the time. Zope even has had its own ABC / interface system, specifically modeled after Java interfaces. stdlib logging is a reimplementation of log4j in Python and so on.
[^1]: https://en.wikipedia.org/wiki/Python_(programming_language)
[^2]: https://en.wikipedia.org/wiki/Java_(programming_language)
(Some changes in Python 3 I can recall: bytes/str/unicode being the biggest one; fixing mutable variables in nested functions; changing some obscure behavior in class hierarchies and overload resolution; changing things like range() and map() to lazy evaluation.)
For better or for worse, Java has maintained very good (not perfect) compatibility throughout, even with painful changes like generics in 1.5, lambdas in 8, modules in 9, eventual removal of applets and SecurityManager, etc. This also contrasts with C#/.NET, which I think had some breaking changes over the decades.
They are basically describing a public API backed by a private type that they can extend, rearrange, or otherwise modify without breaking the public contract.
That way, I can use "normal" naming in `class RealShipOpts:...`, and be explicit that it's not really public for the end users (they should use the `.api` module instead).
(Earliest mention I could find for camelCase methods was 25 years ago: https://github.com/twisted/twisted/blob/d7c19cd40d07c8c37f85... )
Hell no
If you have members that users probably shouldn't touch, you prepend them with an underscore. This is just a hint; It doesn't actually change anything. We're all adults here and we know the consequences of reaching into implementation details.