Introduction to flexitext

Flexitext is a Python library for formatting annotations in matplotlib charts. It allows you to describe which part of a Python string should have specific properties, enabling different styles within the same annotation.

In this introduction to flexitext, we'll cover the basics of the library and the concept of annotations, highlighting its main features. For more complex use cases, check the post on advanced usages of flexitext.

Libraries

First, you need to install flexitext with the following command: pip install flexitext.

Flexitext is one of 2 python libraries that make text formatting for matplotlib easy, along with highlight_text. It was created by Tomás Capretto and is inspired by the R package ggtext.

We'll also need to load matplotlib to create the figure.

import matplotlib.pyplot as plt
from flexitext import flexitext

Simple matplotlib annotation

In matplotlib, we generally use the text() function that have 3 main arguments:

x: the position of the annotation on the x-axis
y: the position of the annotation on the y-axis
s: the text to display

Note: it's possible to change the coordinate system when using the x and y arguments (e.g relative to the data or absolute). Check the dedicated post.

A minimalist example using the text() function would like so:

# Init a figure
fig, ax = plt.subplots(figsize=(8, 8), dpi=200)

text = "Python Graph Gallery"
fig.text(x=0.3, y=0.6, s=text)

# Other ways of using the text() function:
# ax.text(...)
# plt.text(...)

# Display the output
plt.show()

Stylizing text

The syntax of flexitext is somewhat similar to HTML in that you enclose the text whose properties you want to change in <>.

If you want to change the properties of the first word in the Python Graph Gallery text, you change Python to <>Python</>. Then you set the style properties of Python inside the first <>. So, if we want Python to be larger and blue, it becomes :

<color:blue, size:20>Python</> Graph Gallery

Note: properties must be coma separated.

Finally, instead of using the text() function from matplotlib, we use the flexitext() function, which uses the same arguments!

# Init a figure
fig, ax = plt.subplots(figsize=(8, 8), dpi=200)

text = "<color:blue, size:20>Python</> Graph Gallery"
flexitext(x=0.3, y=0.6, s=text)

# Display the output
plt.show()

Which properties can I change?

flexitext supports a fixed number of params at the moment:

alpha: text transparency
backgroundcolor: color in the background of the text
color: text color
family: font family of the text
name: font name of the text
size: size of the text
style: style of the text (italic, oblique...)
weight: weight of the text (bold, thin...)

If we go back to the previous example and use other parameters, we get the following result:

# Init a figure
fig, ax = plt.subplots(figsize=(8, 8), dpi=200)

text = "<color:darkred, size:30, alpha:0.6, style:italic, weight:bold>Python</>"
text += " Graph Gallery"
flexitext(x=0.3, y=0.6, s=text)

# Display the output
plt.show()

Combine styles

Once we understand the basics of flexitext, it becomes easy to create text with various styles!

# Init a figure
fig, ax = plt.subplots(figsize=(8, 8), dpi=200)

text = "<color:darkred, size:30, alpha:0.3, style:italic, weight:bold>Python</>"
text += " <color:skyblue, size:20, weight:bold>Graph</>"
text += " <color:olive, size:30, alpha:0.8, style:italic>Gallery</>"
flexitext(x=0.2, y=0.6, s=text)

# Display the output
plt.show()

Crossed properties

You may want to apply a given property to the first 2 words of a text (bold), but have different properties between these 2 words (different size).

The following example puts the first 2 words in bold, even though these words have a *different size property.

# Init a figure
fig, ax = plt.subplots(figsize=(8, 8), dpi=200)

text = "<weight:bold><size:30>Python</> "
text += "<size:20>Graph</></> "
text += "<size:10>Gallery</>"
flexitext(x=0.2, y=0.6, s=text)

# Display the output
plt.show()

Going further

Contact & Edit

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