Tuesday, August 10, 2021

Why Python Is Weird For C++ Developers -- Some Thoughts

See 9 Reasons Why Python Is Weird For C++ Developers.

I'm often bothered by inter-language comparisons. Mostly because programming languages -- except in the most abstract way -- aren't really very comparable. At the Turing Machine level the finite state automata are comparable, but that reductionist view (intentionally) eliminates all the expressive power from a given language.

Let's look at the reasons in some detail. A few of them actually are interesting.

  1. Whitespace. I'm dismissive of this as an interesting difference. When I read code in EVERY other programming language, I'm immediately aware that programmers can indent. Indeed, I've seen C and C++ code were {}'s were omitted, but the code was indented properly, making it devilishly hard to debug. My experience is that folks get the indentation right BEFORE the get the {}'s right.
  2. Syntax. In this article, it's the lack of {}'s. Again, I'm dismissive because I've actually helped folks learning C++ who had the indentation right and the {}'s wrong. This is ony "weird" if you're absolutely and completely convinced that {}'s are somehow a divine requirement that transcends all human attempts at interpretation. With Unicode, we're in a position to separate set membership from block-of-code and start using multiple variants on {}'s.  I'd vote for if a > b 【m = a】else 【m = b】 using 【】for code blocks.
  3. Class Variables. This points out an inherent ambiguity of C++. Most of the time, most things are not "static". They're "automatic" that is, associated with the instance. The auto keyword, however, is rarely used, and is mostly assumed. Python (outside dataclasses) is more consistent. All things inside the class statement are "static": part of the class. In the case of dataclasses, this simple rule is broken, which can be confusing. But. This wasn't mentioned.
  4. Pointer and Reference Transparency. This is simple confusion. All Python is handled by reference all the time. C++ is an absolute mess of "primitive" types that don't use references and objects that do use references. Java is just as bad. And I want to emphasize bad. Python is perfectly consistent, and -- I would suggest -- the opposite of weird. But. The article is describing things from a C++ perspective, as if C++ were somehow not weird. I suggest this isn't a great approach.
  5. Private Class Members. This is summarized as "better encapsulation and control" without a concrete example. It's hard to provide a concrete example because the Pythonic approach works so well. The only use case for "private" that I've been able to understand is when you're concealing the entire implementation from all scrutiny. That is, you have a proprietary implementation with an encrypted JAR file and you want to avoid revealing it to protect some intellectual property. Since Python is source, this can't happen, and we say "We're all adults here." Flag it with a leading _ and we'll recognize it as part of an implementation detail that might change. 
  6. Self vs. this. Not sure what this is but the phrase "only major programming language" is something that relies on Java and C++ being near the top of the TIOBE index. I suspect we can find a lot of languages that use neither "self" nor "this". I'm not sure exactly how this is weird, but, I get that it's different.
  7. Multiple Return Values. This seems like an intentional refusal to understand how tuples and tuple unpacking work. Again, this seems to make C++ the yardstick when C++ is clearly kind of weird here.
  8. No Strong Data Types. This seems like another refusal to understand Python. In this case, it feels like it's a refusal understand that objects are strongly typed in Python and variables are transient labels attached to objects. The mypy tool will try to associate a type with a variable and will warn you about a = "string" followed by a = 42. Perhaps I'm not understanding, but the portrayal of C++ rules as "not weird" seems like it's being taken too far. 
  9. No Constants. This isn't completely true. Some folks use enums to provide enumerated numeric constant values in the rare cases where this might matter. Using global variables as constants actually works out fine in practice. Most tools will look for ALL_CAPS names on the left of an = sign; and if this occurs more than once will raise a warning. If you have really stupid fellow programmers who can't understand how some variables shouldn't be reused, you can easily write a script to walk the AST looking for references to global variables and warn your colleagues that there are rules and they're not following them. This is part and parcel of the "We're all adults here" approach. If folks can't figure out how constants work, you need to collaborate more fully with other developers to help them understand this.

I'm unhappy with lifting up C++ quirks as if they're somehow really important. I don't think C++ is a terribly helpful language. The need for explicit memory management, for example, is a terrible problem. The explicit distinction between primitives and objects is also terrible.

While compare-and-contrast with Python might be helpful for C++ expatriates, I think this article has it exactly backwards. I think the following list couuld be more useful.

  • Python frees you from counting {}'s. Just indent. It's easier.
  • Python has simple rules for class/instance variables (except in the case of dataclasses and named tuples.) Also: if it starts with self. it's an instance variable.
  • Python is all references without the horrifying complexity of primitive types.
  • We're all adults here. Don't stress yourself out over privacy or constants. Document your code, instead. Write a unit test case or two. Use mypy. Use black.
  • Tuple unpacking and the fact that tuples are often implied works out very nicely to create very clean code.
  • Data types are part of the object. There's no magical "cast" capability to process a block of bytes as if they're some other type. 
These are advantages of Python. And disadvantages of C++. I think it's better to talk about what Python has than what Python lacks when measured against a terribly complex language like C++.

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