BUG: `pandas.Styler.__repr__` and `pandas.Styler.__str__` cause `nbconvert` failure to display data

[yasirroni]

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Reproducible Example

from IPython.display import display, HTML

import numpy as np
import pandas as pd

df = pd.DataFrame(np.random.random((2,3)))
display(df)  # this will send print(df) to  "text/plain": [...]

df_style = df.style.set_caption("data")
display(df_style)  # this will send print(df_style) to  "text/plain": [...]

Issue Description

Refer to my issue in nbconvert

Basically, nbconvert use what is in "text/plain": [...]. Displaying something using display seems to send object.__repr__ or object.__str__ there. Sadly, pd.style.Styler return <pandas.io.formats.style.Styler at 0x...> on print. Please at least change pd.style.Styler.__repr__ and pd.style.Styler.__str__ into a human readable meaningful text, that is, at least, sending pd.style.Styler.data.__repr__ and pd.style.Styler.data.__str__.

Expected Behavior

pd.style.Styler.__repr__ and pd.style.Styler.__str__ has a human readable and meaningful text, that is, at least, like pd.style.Styler.data.__repr__ and pd.style.Styler.data.__str__.

Installed Versions

I use python 3.8, pd.show_versions throws error.

Here is pandas version: '2.0.3'

[Dhayanidhi-M]

Hi @yasirroni ,

I am new contributor. Trying to understand the issue here. Could you explain what exact text you are looking for ?

[yasirroni]

@Dhayanidhi-M I'm not looking any text. I'm reporting a bug or requesting feature that pd.style.Styler should have human readable string representation on .__str__ or .__repr__ to be compatible with nbconvert. That is because cell metadata on "text/plain": [...] store what is in .__str__ or .__repr__ as far as I know.

[rhshadrach]

Simpler reproducer:

df = pd.DataFrame(np.random.random((2,3)))
print(df)
#           0         1         2
# 0  0.107940  0.910253  0.657357
# 1  0.939727  0.032391  0.775682

df_style = df.style.set_caption("data")
print(df_style)
# <pandas.io.formats.style.Styler object at 0x7faf0fd21b10>

I think it makes sense to have the 2nd output match the first.

cc @attack68

[attack68]

Thanks for cc

Just to keep this in perspective, this is not a bug, it is a feature request for something that has not been in scope previously.

Jupyter notebooks have a specific order of analysing the repr methods for objects in the last line of a cell. A Styler can be represented in HTML format in a notebook becuase its __repr_html__ method by default returns a string of HTML.

If the pandas option styler.render.repr is "latex" then the __repr_html__ method returns None and the __repr_latex__ method returns a string of LaTeX. This is how nbconvert is configured to work for those formats, in general.

In your case, by using the print function you are forcing Python to call the __str__ or __repr__ method, which do not exist for a Styler.

The fastest way of getting results in this case would be to note that Styler.to_string() exists in a basic form, so that __str__ could be mapped to called self.to_string()

print(df.style.to_string())
#  0 1 2
# 0 0.554557 0.202806 0.479053
# 1 0.745892 0.921658 0.324225

I would ask, ultimately, what do you want to achieve by using a Styler in an nbconvert without adding any styles? Why not just call a DataFrame, since the to_string method of a Styler serves no purpose beyond the normal string representation for a DataFrame?

[yasirroni]

Thanks, @attack68.

The most basic thing is that we commonly did not print in notebook, right? We often just write like this in cell,

df = pd.DataFrame(np.random.random((2,3)))
df.style.set_caption("data")

Or sometimes, store the style,

df = pd.DataFrame(np.random.random((2,3)))
styled = df.style.set_caption("data")
styled

That works just fine, a styled DataFrame will appear in the output, no need any fancy method

---

But, that output vanished in pdf due to nbconvert looking for "text/plain": [...].

So, whatever that pandas choose to use, the rationale is that running jupyter nbconvert --to pdf PATH should print at least non-styled table. Thus passing anything useful, at least "text/plain": [...], is expected.

If later the pandas community decided to support HTML, LaTeX, or images, it can be in future scope I think.