Conditional chunk for python quarto docs

[boshek]

Description

Is it possible to conditionally evaluate a chunk based on an environment variable in python quarto docs?

You can include content conditionally really nicely in R a la:

---
format: html
---

conditional _does_ work

```{r}
#| eval: false
1+2
```

but obviously this syntax is an issue

```{r}
#| eval: !expr Sys.getenv("VAR") == 'production'
1+1
```

I didn't expect the following to work but I wanted to share to illustrate the type of thing I am doing. I see this section on conditional content but I think that is restricted to output type. My exact use case is wanting to not evaluate some chunks when I publish something to confluence hence wanting to evaluate on a environment variable:

---
format: html
---

conditional _does_ work

```{python}
#| eval: false
1+2
```

but obviously this syntax is an issue

```{python}
#| eval: !expr python import os; os.getenv('VAR') == 'production'

1+1
```

That fails with this error:

ERROR:

could not determine a constructor for the tag '!expr'> in "", line 1, column 7:
eval: !expr python import os; os.geten ...

[jimjam-slam]

Unless you have a burning need for the conditional execution logic to not show up in your final output, I feel like it might just be easier to put that logic in the chunk itself:

```{python}
python import os

if os.getenv('VAR') == 'production':
    1+1
```

[boshek]

Thanks for this. Yeah certainly this works. I was just uncertain if there was a quarto-esque way of doing it.

[mcanouil]

Not at this point, but a cross-engine / language agnostic way is on the radar (no timetable).

[mcanouil]

!expr is a knitr specific feature that happens to work (partially, depending on where) inside Quarto.

Jupyter does not have a similar feature.

So, two options:

• do as suggested by internalising the logic as code rather than YAML option (which is the same and possibly more readable as there is no !expr "string expression" thing.
• use knitr as engine with reticulate.

[remlapmot]

I also needed this.

I came up with an alternative solution - use inline code expressions with inline ifs to write Quarto's conditional content syntax around the sections of Quarto code you want to include/exclude. E.g.

---
format: html
---

```{python}
#| include: false
from IPython.display import Markdown
```

```{python}
hide_some_things = True
```

`{python} Markdown("::: {.content-hidden}") if hide_some_things else None`

```{python}
print("Hidden")
```

`{python} Markdown(":::") if hide_some_things else None`

```{python}
print("Shown")
```

It will be great when this feature is added to Quarto.

[boshek]

Oh I did not realize that you could do in line syntax for python! Thanks for this and ☝️ .

[remlapmot]

My pleasure, using inline code to toggle Rmd/Qmd syntax is really an old trick from R Markdown docs.

In case useful, I also got the same thing working with Julia.

---
format:
  html:
    embed-resources: true
engine: julia
---

```{julia}
#| include: false
using Markdown
hide_solutions = true
```

`{julia} hide_solutions ? md"::: {.content-hidden}" : md""`

```{julia}
println("Hidden")
```

`{julia} hide_solutions ? md":::" : md""`

```{julia}
println("Shown")
```

[boshek]

Yeah I'd always known the inline R but I thought that was a knitr feature. This is great news.

[mcanouil]

It is a knitr feature, until it became a Quarto feature in 1.4 for Python/Julia.