this post was submitted on 21 Nov 2024
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Python allows programmers to pass additional arguments to functions via comments. Now armed with this knowledge head out and spread it to all code bases.

Feel free to use the code I wrote in your projects.

Link to the source code: https://github.com/raldone01/python_lessons_py/blob/v2.0.0/lesson_0_comments.ipynb

Image transcription:

# First we have to import comment_arguments from arglib
# Sadly arglib is not yet a standard library.
from arglib import comment_arguments


def add(*args, **kwargs):
    c_args, c_kwargs = comment_arguments()
    return sum([int(i) for i in args + c_args])


# Go ahead and change the comments.
# See how they are used as arguments.

result = add()  # 1, 2
print(result)
# comment arguments can be combined with normal function arguments
result = add(1, 2)  # 3, 4
print(result)

Output:

3
10

This is version v2.0.0 of the post: https://github.com/raldone01/python_lessons_py/tree/v2.0.0

Note:

v1.0.0 of the post can be found here: https://github.com/raldone01/python_lessons_py/tree/v1.0.0

Choosing lib as the name for my module was a bit devious. I did it because I thought if I am creating something cursed why not go all the way?

Regarding misinformation:

I thought simply posting this in programmer humor was enough. Anyways, the techniques shown here are not yet regarded best practice. Decide carefully if you want to apply the shown concepts in your own code bases.

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[–] [email protected] 205 points 1 month ago (11 children)

IMO comments should never ever be parsed under any circumstances but I probably don't know enough to really speak on this

[–] [email protected] 91 points 1 month ago

No, your intuition is correct, this is extremely cursed.

[–] [email protected] 62 points 1 month ago* (last edited 1 month ago) (1 children)

Seen in a code review (paraphrased):

image of a program which is estimating the size of an array by counting how many lines of source code were used to construct it

"Why does this break when you add comments in the middle?"

[–] [email protected] 16 points 1 month ago (3 children)

Why would python even expose the current line number? What’s it useful for?

[–] [email protected] 38 points 1 month ago* (last edited 3 weeks ago)

On a serious note:

This feature is actually very useful. Libraries can use it create neat error messages. It is also needed when logging information to a file.

You should however never ever parse the source code and react to it differently.

[–] [email protected] 24 points 1 month ago

You underestimate the power of us, print debuggers.

[–] [email protected] 17 points 1 month ago (1 children)

Why wouldn't it? Lots of languages do. In C++ you have __LINE__.

[–] [email protected] -3 points 1 month ago

Because it doesn't seem like a useful feature. The only occasion I imagine this could be helpful is with logging to the console to track when the function breaks, but even then - still trivial to replace.

[–] [email protected] 18 points 1 month ago

The add function in the example above probably traverses the call stack to see what line of the script is currently being executed by the interpreter, then reads in that line in the original script, parses the comment, and subs in the values in the function call.

This functionality exists so when you get a traceback you can see what line of code triggered it in the error message

[–] [email protected] 8 points 4 weeks ago (1 children)

Can we just clarify that you mean that comments should never be parsed by the language engine. There are valid annotation systems, but the goal is alway to ensure that one passable can never impact the other.

Imagine if here a comment could create a syntax error! This is even worse for runtime scripting languages like python.

[–] [email protected] 9 points 4 weeks ago (1 children)

Sure, but let's just clarify that this is someone going out of their way to create this problem, using Python's ability to read it's own code.

Basically, you can load any text file, including a source code file, and do whatever you want with it.

So, a function can be written that finds out whatever's calling it, reads that file, parses the comments, and uses them as values. This can also be done with introspection, using the same mechanism that displays tracebacks.

[–] [email protected] 1 points 3 weeks ago* (last edited 3 weeks ago)

Conveniently Python keeps the comments around. 😄

[–] [email protected] 5 points 1 month ago (1 children)

This isn't standard python. lib is not in the standard library. Python also doesn't have any special variables where it stores comments, other than __doc__ which stores a docstring. If I had to guess, add is reading the file/REPL via __file__.

[–] [email protected] 1 points 4 weeks ago* (last edited 4 weeks ago) (1 children)

Is __doc__ storing a comment or just a text string?

[–] [email protected] 2 points 4 weeks ago

It's a string, although sometimes Python conflates the two. The recommended way to make a multi-line comment is to just make a multi-line string and just don't use it.

[–] [email protected] 4 points 1 month ago (2 children)

Comments should be removed before shipping.

[–] [email protected] 7 points 1 month ago (1 children)

Python is an interpreted language but for a compiled language absolutely (and obviously).

[–] [email protected] 2 points 4 weeks ago

I guess there could be just a script before deployment.

[–] [email protected] 4 points 1 month ago* (last edited 3 weeks ago)

Well now that causes breakage two dependencies down the line. Good luck with that. 😅

[–] [email protected] 3 points 1 month ago

Ignoring lint issues comes to mind as an at least somewhat reasonable use case.

[–] [email protected] 3 points 1 month ago

One case where I find it useful, tho it operates in a more limited way, is code in block blocks within code comments in Rust, which are also printed out in the generated documentation. They essentially get ran as part of your unit tests. This is great for making sure that, eg, your examples left in code comments actually work, especially if they’re written in a way that functions like a unit test.

[–] [email protected] 2 points 1 month ago

Some languages use the comments to generate documentation. Something like

// function to add two numbers func Add(num1 int, num2 int)

[–] [email protected] 2 points 1 month ago
[–] [email protected] 2 points 1 month ago (1 children)

It's quite useful to parse comments and generate documentation from them, either as plain old hypertext or in your editor with LSP.

[–] [email protected] 5 points 1 month ago (2 children)

That sounds fine if you have something reading the file independently. But the actual executable code should not be able to access its own comments.

[–] [email protected] 1 points 4 weeks ago

Comments aren't normally accessible unless you (independently) open and read the source code file as you would with any arbitrary file.

[–] [email protected] 1 points 4 weeks ago* (last edited 4 weeks ago)

capability is fine. Conflation is stupid. You can also use code to erase itself, but thinking that's a good idea is generally wrong. But to remove that, you also remove the general ability to erase files.