Is there a way to include a comment in an f-string?

Question

It would be useful for mo to include a comment in an f-string. For instance, take this code:

f"""
<a
   href="{ escape(url) }"
   target="_blank" { # users expect link to open in new tab }
>bla</a>
"""

It would be nice if this code was equivalent to:

f"""
<a
   href="{ escape(url) }"
   target="_blank" 
>bla</a>
"""

You can include full Python expressions in between the curly brackets, but it looks like you can't include comments. Am I correct? Is there a way to do this?

What you can do instead is this: `>>> x=1;y=2 >>> data="""x: {x}, y: not wanted""" >>> data 'x: {x}, y: not wanted' >>> data.format(**locals()) 'x: 1, y: not wanted' >>> data.format(**globals()) 'x: 1, y: not wanted' ` While ugly, it doesn't throw an exception and kind of preserves f-string behavior. However use Jinja or something sane instead of misusing f-strings. — Peter Badida, May 23 '20 at 13:15
Are you constructing the `html` string yourself or getting it from somewhere else? It's unclear to me what you're doing. — Pedro Lobito, May 23 '20 at 17:56
@CONvid19 I used the example of HTML because I thought it would be simpler. In reality, I'm actually building an SQL query. — Flimm, May 23 '20 at 17:57
With your rep, I'd expect you to know how to [ask a good question](https://stackoverflow.com/help/how-to-ask), specifically, describe exactly what you're trying to do, which is clearly not the case when you use an `html` example while trying building an `SQL` query. — Pedro Lobito, May 23 '20 at 18:06
@CONvid19 I can't tell you how frustrating it is to look for answers for a question X, find the exact question on SO, only to find that commentators demanded extra details, making the question much more narrow, so that they could answer the Y problem, rather than the question X, and so I have to keep looking for the answer to the question X. I know what the XY problem is, but not every question X actually needs an answer to Y, most of the time, I actually need the answer to the question that I asked! — Flimm, May 23 '20 at 20:35
Sorry to rant, but you've accidentally touched a sore point with my experience of SO. — Flimm, May 23 '20 at 20:36

score 7 · Accepted Answer · answered May 23 '20 at 13:11

7

From PEP498:

Comments, using the '#' character, are not allowed inside an expression.

There is no way to comment other than putting a '#' character in Python, so it is not possible.

answered May 23 '20 at 13:11

Asocia

5,441
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***There is no way to comment other than putting a '#'***, not true, try `""" some comment """` – Pedro Lobito May 23 '20 at 17:36
2

@CONvid19 I think you are talking about docstrings. They don't have to be surrounded with triple quotes. They are not comments, and they wouldn't work in this situation. – Flimm May 23 '20 at 17:57
They are technically not comments, but they are used as so, namely, multi-line comments. [Is there a way to create multiline comments in Python?](https://stackoverflow.com/questions/7696924/is-there-a-way-to-create-multiline-comments-in-python) – Pedro Lobito May 23 '20 at 17:59
1

@CONvid19 You can index a tuple with boolean and use it like a ternary operator but does that make it *really* ternary operator? No. It's same thing. You can use some triple quoted string in your code, and expect from your readers to interpret them like comments but for Python they are *still* strings: `>>> 5 + 5 """ is this a comment? """` Nope, `SyntaxError` it is. – Asocia May 23 '20 at 20:39

score 1 · Answer 2 · answered May 23 '20 at 13:34

1

No. There is no comment in f-string.

When building a str, template engines may be overkill. Joining a list of str may be desirable.

s = ''.join([
    '<a',
    f' href="{escape(url)}"',
    ' target="_blank">',
    # users expect link to open in new tab
    'bla</a>',
])

answered May 23 '20 at 13:34

Aaron

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Unmaintainable in the long run if multiple people edit the same codebase and e.g. skip commas, forget quotes. Unfortunately this is a recipe for disaster if a test suite won't catch it before deployment. – Peter Badida May 23 '20 at 13:37

score 1 · Answer 3 · answered May 23 '20 at 13:41

You cannot write a comment inside an expression. But you can write a string in multiple fragments and write a comment between 2 fragments provided the next fragment starts on a different line:

s = (f"""
<a
   href="{ escape(url) }"
   target="_blank" """ # users expect link to open in new tab
f""">bla</a>
""")

Is there a way to include a comment in an f-string?

3 Answers3