In dashboard, `plt.show()` show intermediate matplotlib output

[cderv]

---
title: "Reproducible Quarto Document"
format: 
  html: default
  dashboard: default
engine: jupyter
---

```{python}
#| echo: false
import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5, 10]
p = plt.boxplot(x)
plt.title("Test");
plt.show()
```

We get this in HTML

And this in dashboard

Suppressing plt.show() output is ok :

plt.show();

So it seems we don't consider output the same in Dashboard and HTML, and that supressing output with ; is required with matplotlib show()

If this is expected, we should probably document the difference. Though I am surprised - hence why I open the issue for future reference.

[stragu]

Another example below, This is for a .py source file rendered with quarto render dashboard.py.

It shows that the issue happens even without using plt.show(), and affects seaborn too. Same happens when editing e.g. axis labels with plt.xlabel() and plt.ylabel().

Workarounds are:

• suppressing the output of the last command, or
• assigning all commands to variables

Using following versions:

• quarto 1.6.39
• matplotlib 3.9.3
• seaborn 0.13.2
• python 3.11.10

# %% [markdown]
# ---
# title: "title and label outputs shown in dashboards"
# format: dashboard
# ---

# %% [markdown]
"""
## matplotlib only
"""

# %%
#| title: only matplotlib, no modification of title or labels
import matplotlib.pyplot as plt
x = [1, 2, 3, 4, 5, 10]
plt.boxplot(x)

# %%
#| title: "workaround: output suppressed by appending semicolon"
plt.boxplot(x);

# %%
#| title: only matlplotlib, with plt.title()
plt.boxplot(x)
plt.title("Test")

# %%
#| title: "workaround: output suppressed for last command"
plt.boxplot(x)
plt.title("Test");

# %%
#| title: "alternative workaround: assign each command to variables"
some_var = plt.boxplot(x)
some_var = plt.title("Test")

# %% [markdown]
"""
## seaborn
"""

# %%
#| title: seaborn on its own
import seaborn as sns
sns.boxplot(y = x)

# %%
#| title: seaborn + plt.title(), same issue
sns.boxplot(y = x)
plt.title("Test")

# %%
#| title: seaborn with its own set_title() method, same issue
sns.boxplot(y = x).set_title("Test")

# %%
#| title: workaround suppressing output works too for plt.title()
sns.boxplot(y = x)
plt.title("Test");

# %%
#| title: workaround suppressing output works too for set_title()
sns.boxplot(y = x).set_title("Test");

[stragu]

I've revisited the issue today because many learners were seeing it.

• testing with:
  • Quarto 1.9.37
  • matplotlib 3.10.9
  • seaborn 0.13.2
  • Python 3.13.3
• html format is also affected, but slightly less: cell 3 only prints the dict (as opposed to both the dict and Text() in the dashboard)
• there's a third workaround that works for variables of type matplotlib.axes._axes.Axes (e.g. what seaborn.<...>plot() and pandas.plot() return): using the .set() method for titles and axis labels.

Here is the updated qmd, including echoed code:

---
title: "dict, title and label outputs shown in dashboards"
format:
    dashboard:
        scrolling: true
echo: true
---

# matplotlib only

## single command

```{python}
#| title: "only matplotlib, no modification of title or labels: prints dictionary"
import matplotlib.pyplot as plt
x = [1, 2, 3, 4, 5, 10]
plt.boxplot(x)
```

```{python}
#| title: "workaround 1: output suppressed by appending semicolon"
plt.boxplot(x);
```

## with title

```{python}
#| title: "only matlplotlib, with plt.title(): prints both dict and Text()"
plt.boxplot(x)
plt.title("Test")
```

```{python}
#| title: "workaround 1 (on last command) also works"
plt.boxplot(x)
plt.title("Test");
```

```{python}
#| title: "workaround 2: assign (all sources of outputs) to variables"
some_var = plt.boxplot(x)
some_var = plt.title("Test")
```

# seaborn

## with title() method

```{python}
#| title: "seaborn on its own is clean"
import seaborn as sns
sns.boxplot(y = x)
```

```{python}
#| title: "seaborn + plt.title(), same issue"
sns.boxplot(y = x)
plt.title("Test")
```

```{python}
#| title: "workaround 1 works too for plt.title()"
sns.boxplot(y = x)
plt.title("Test");
```

## with "set" methods

```{python}
#| title: "seaborn with its own .set_title() method, same issue"
sns.boxplot(y = x).set_title("Test")
```

```{python}
#| title: "workaround 1 works too for .set_title() method"
sns.boxplot(y = x).set_title("Test");
```

```{python}
#| title: "workaround 3: use .set() method on any variable of type matplotlib.axes._axes.Axes"
sns.boxplot(y = x).set(title = "Test")
```

[cderv]

I have a PR that should handle the cases correctly by detecting more cases we were missing.