Rendering Images in pandas DataFrame to_html Formatters

When working with pandas DataFrames, it’s not uncommon to need to render images or other HTML elements within the dataframe’s values. The to_html method provides a convenient way to do this, but there are some nuances to be aware of when using formatters to achieve this.

In this article, we’ll explore how to use the to_html method with formatters to display images in a pandas DataFrame. We’ll delve into the details of how formatters work and provide examples of how to render images within the dataframe’s values.

Understanding Formatters

Formatter is a function that takes the value of an element as input and returns the HTML representation of that value. When using the to_html method with a formatter, pandas will call this function for each element in the dataframe before rendering it.

df.to_html(formatters={'Last Run Rank Difference': lambda x: check_html_val_for_arrow(x)})

In this example, the check_html_val_for_arrow function is called for the values in the ‘Last Run Rank Difference’ column. The return value of this function is then used to render the element as HTML.

Escape Behavior

One important thing to note when using formatters with the to_html method is that pandas will escape any HTML characters within the dataframe’s values by default. This means that if you try to use an <img> tag directly in your formatter, it won’t work.

For example:

def check_html_val_for_arrow(x):
    try:
        if x > 0:
            return str(x) + ' <img src="cid:image7">'
        elif x < 0:
            return str(x) + ' &lt;img src="cid:image8"&gt;'
        else:
            return str(x)
    except:
        return str(x)

df = pd.DataFrame([[1, '<img src="cid:image7">', 2]]])
df.to_html(formatters={'col1': lambda x: check_html_val_for_arrow(x)})

In this example, the check_html_val_for_arrow function returns an <img> tag, but since pandas is escaping any HTML characters, the <img> tag will be rendered as plain text.

To avoid this behavior, we can use the escape=False parameter when calling to_html. This tells pandas to not escape any HTML characters:

my_img_snippet = (
    "<img src='https://www.pnglot.com/pngfile/detail/"
    "208-2086079_right-green-arrow-right-green-png-arrow.png'>"
)
df = pd.DataFrame([[my_img_snippet]])
HTML(df.to_html(escape=False))

In this example, the my_img_snippet variable contains an <img> tag with a src attribute set to a valid image URL. When we call to_html on this dataframe, pandas will not escape any HTML characters, and the <img> tag will be rendered correctly.

Styler Object

Another way to achieve this behavior is by using the styler object provided by pandas. The styler object can handle the rendering of elements, including images, without the need for formatters:

df.style

In this example, we’re simply calling style on the dataframe, which will render it with the specified styling.

Using Images in Formatters

Now that we’ve explored how to avoid escaping HTML characters and use the styler object, let’s talk about using images in formatters. To do this, you can create a function that returns an <img> tag with the desired image URL:

def check_html_val_for_arrow(x):
    try:
        if x > 0:
            return str(x) + ' <img src="cid:image7">'
        elif x < 0:
            return str(x) + ' &lt;img src="cid:image8"&gt;'
        else:
            return str(x)
    except:
        return str(x)

def render_arrow_img(val):
    my_img_snippet = (
        "&lt;img src='https://www.pnglot.com/pngfile/detail/"
        "208-2086079_right-green-arrow-right-green-png-arrow.png'&gt;"
    )
    if val > 0:
        return f'<span style="color: green;">{val}</span> &lt;{my_img_snippet}>'
    elif val < 0:
        return f'<span style="color: red;">{val}</span> &lt;{my_img_snippet}>'
    else:
        return str(val)

df.to_html(formatters={'Last Run Rank Difference': render_arrow_img})

In this example, the render_arrow_img function returns an <img> tag with the desired image URL. The to_html method is then called on the dataframe with a formatter that uses this function.

Conclusion

When working with pandas DataFrames and using the to_html method, there are some nuances to be aware of when it comes to formatters and escaping HTML characters. By understanding how formatters work and using techniques like escape=False or the styler object, you can render images within your dataframe’s values.

Last modified on 2025-04-22