Python data loader f-string problem?

[dkrasne]

I have a Python data loader that ran fine on my own machine, but it failed on the Observable Framework build for what it claimed was a problem with a closing ] in an f-string. I'm not sure if this is possibly a bug on the Framework end, or on the Node.js end, or if the issue is something else, so I'm posting here instead of in Issues.

The error that I got from the GitHub deploy log is:

13:05:59.417Z
build
-
copy src/data/nodegoat_data.json → load /data/nodegoat_data.json → [missing] stderr:   File "/project/src/data/nodegoat_data.json.py", line 574
13:05:59.430Z
build
-
    new_word = word_instance_df.query(f"obj_id == '{row2["wd_sub_id"]}'").reset_index(drop=True)
13:05:59.430Z
build
-
                                                          ^^^^^^^^^
13:05:59.430Z
build
-
SyntaxError: f-string: unmatched '['
13:05:59.432Z
build
-
error in 14ms: loader exited with code 1
13:05:59.432Z
build
-
stderr: 
13:05:59.432Z
build
-
Unexpected error: loader exited with code 1
13:05:59.432Z
build
-
stderr: The full error follows
13:05:59.432Z
build
-
13:05:59.433Z
build
-
stderr: file:///project/node_modules/@observablehq/framework/dist/loader.js:430
13:05:59.433Z
build
-
      throw new Error(`loader exited with code ${code}`);
13:05:59.433Z
build
-
            ^
13:05:59.433Z
build
-
13:05:59.433Z
build
-
Error: loader exited with code 1
13:05:59.433Z
build
-
    at CommandLoader.exec (file:///project/node_modules/@observablehq/framework/dist/loader.js:430:13)
13:05:59.433Z
build
-
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
13:05:59.433Z
build
-
    at async file:///project/node_modules/@observablehq/framework/dist/loader.js:373:11
13:05:59.433Z
build
-
13:05:59.433Z
build
-
Node.js v20.17.0
13:06:00.397Z
finalizing
-
Aborting build due to error
13:06:00.397Z
build
-
Error with build: Command failed exitCode: 1

But there's not actually a problem with that f-string, the bracket is closed properly, and the single/double quotes are properly alternated. Assigning the interpolated bit to a variable and putting that into the f-string instead worked fine when deployed, but it should have worked the first time around.

Thanks in advance!

[Fil]

shouldn't the internal double-quotes be escaped?

- f"obj_id == '{row2["wd_sub_id"]}'"
+ f"obj_id == '{row2[\"wd_sub_id\"]}'"

[dkrasne]

Not to my knowledge -- they're not text, and not having to escape them is the whole point of alternating single and double quotation marks. (And, as I said, it worked fine on my own machine.) But I'll look into it.

[Fil]

The surprising thing is that it runs on one machine and not on the other. Maybe some differences between python versions? Or platform?

I'd try this (but I'm shooting in the dark):

f"""obj_id == '{row2["wd_sub_id"]}'"""

[dkrasne]

Yeah, I agree that's the strange thing. Since it works fine after assigning the dictionary item to a variable, I'm not going to test the triple quotation marks now, but if I run into the situation again I'll give it a shot. (Presumably it will work fine -- but of course still doesn't solve the original mystery.)

[mythmon]

Python 3.12 changes f-strings to allow internal quotes of the same type as the external quotes without escaping. Python 3.11 and below will have problems with syntax. What version of Python are you using?

[dkrasne]

I learned on Python 3.11 and used it almost exclusively until just a few weeks ago (when I got a new computer), so my syntax should be 3.11-kosher. I don't know what version of Python is on Observable's servers, though (or whatever it is that would cause the failed build).

[mythmon]

Observable Cloud uses Python 3.11.

The "quotes in f-strings" syntax definitely doesn't work on Python 3.11, and only works in 3.12 and above.

❯ nix-shell -p python311 --run python
Python 3.11.13 (main, Jun  3 2025, 18:38:25) [GCC 14.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> x = {'a': 1}
>>> f"x.a is {x["a"]}"
  File "<stdin>", line 1
    f"x.a is {x["a"]}"
                 ^
SyntaxError: f-string: unmatched '['
>>>

❯ nix-shell -p python312 --run python
Python 3.12.11 (main, Jun  3 2025, 15:41:47) [GCC 14.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> x = {'a': 1}
>>> f"x.a is {x["a"]}"
'x.a is 1'
>>>

[dkrasne]

Ah, but your example uses double quotes the whole way through. I interleave single and double, which should work on 3.11.

[mythmon]

I'm not a Python expert, but your sample code works in 3.12 and doesn't work in 3.11. Either way, it doesn't work on Observable Cloud. You'll need to update your code to pull row2["wd_sub_id"] into an intermediate variable.

❯ nix-shell -p python312 --run python
Python 3.12.11 (main, Jun  3 2025, 15:41:47) [GCC 14.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> row2 = {"wd_sub_id": 1}
>>> f"obj_id == '{row2["wd_sub_id"]}'"
"obj_id == '1'"

❯ nix-shell -p python311 --run python
Python 3.11.13 (main, Jun  3 2025, 18:38:25) [GCC 14.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> row2 = {"wd_sub_id": 1}
>>> f"obj_id == '{row2["wd_sub_id"]}'"
  File "<stdin>", line 1
    f"obj_id == '{row2["wd_sub_id"]}'"
                        ^^^^^^^^^
SyntaxError: f-string: unmatched '['

[dkrasne]

Thanks for testing it! Yes, I'd already substituted a variable before making my original post, but I was trying to understand why it didn't work the other way. Clearly the Python version is the culprit, although I don't know how I've gotten other code with interleaved single/double quotes to work in the past! :)