Python Caveats #1: How to put multiline comments in Python dict?

How to put multiline comments in python dict? Should we use triple quotes style or multiline hashes?

May 22, 2019 - 3 minute read -
python python-caveats

Let’s say we have a Python dict and we were to document the general format of the key-value pairs. For the lack of a better example, let’s take the following dict as an example:

family = {
    "goku": {
        "name": "Goku",
        "race": "Saiyan",
        "aliases": ["Son Goku", "Kakarot"],
    },
    "chi-chi": {
        "name": "Chi Chi",
        "race": "Human",
        "aliases": ["The Ox-Princess"],
    },
    "gohan": {
        "name": "gohan",
        "race": "Saiyan",
        "aliases": ["Great Saiyaman", "Son Gohan"],
    },
}

The general format of the key-value pair is:

"username": {
    "name": "",
    "race": "",
    "aliases" [],
}

And to add this as comment, we might try this:

family = {
    """
    General format of entries is

    "username": {
        "name": "",
        "race": "",
        "aliases" [],
    }

    """
    "goku": {
        "name": "Goku",
        "race": "Saiyan",
        "aliases": ["Son Goku", "Kakarot"],
    },
    "chi-chi": {
        "name": "Chi Chi",
        "race": "Human",
        "aliases": ["The Ox-Princess"],
    },
    "gohan": {
        "name": "gohan",
        "race": "Saiyan",
        "aliases": ["Great Saiyaman", "Son Gohan"],
    },
}

Let’s check the keys of this dict now.

In [15]: family.keys()
Out[15]: 
['\n    General format of entries is\n\n    "username": {\n        "name": "",\n        "race": "",\n        "aliases" [],\n    }\n\n    goku',
 'gohan',
 'chi-chi']

Hold up! Why’d that modify the goku string? This is because surrounding something with """ doesn’t necessarily mean as comments in Python. It is just a multiline string. Imagine it as a string literal, which isn’t assigned to any variable. There’s no such thing as multiline comments in Python, unlike other programming languages. The right way to put multiline comments is by using #.

You’d recall using """ to put comments at the beginning of function/class, also otherwise known as docstrings. Well, what do you know, those docstrings aren’t really comments. It is just a string literal and a standard convention[1].

So the right way to put a comment in dict would be

family = {

    # General format of entries is
    # "username": {
    #    "name": "",
    #    "race": "",
    #    "aliases" [],
    # }

    "goku": {
        "name": "Goku",
        "race": "Saiyan",
        "aliases": ["Son Goku", "Kakarot"],
    },
    "chi-chi": {
        "name": "Chi Chi",
        "race": "Human",
        "aliases": ["The Ox-Princess"],
    },
    "gohan": {
        "name": "gohan",
        "race": "Saiyan",
        "aliases": ["Great Saiyaman", "Son Gohan"],
    },
}

tl;dr

There’s no such thing as multiline comment in Python. Use # at every line to truly create multiline comments.

[1] PEP 257 – Docstring Conventions

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