5 Best Ways to Add a Variable to Python plt Title

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πŸ’‘ Problem Formulation: When creating plots in Python using Matplotlib, it’s common to want to include variable values within the title of the plot for dynamic updates and information clarity. For instance, if plotting the growth of a user base over time, one might wish to include the current year in the chart title such as “User Growth in 2023”. This article demonstrates five methods to interpolate or concatenate a variable with a string to dynamically update a plot’s title in Matplotlib.

Method 1: String Concatenation with +

Using string concatenation with the + operator is one of the simplest ways to add variables to the plot title in Matplotlib. Ensure the variable is converted to a string using the str() function before concatenation to avoid type errors.

Here’s an example:

# Import Matplotlib's pyplot
import matplotlib.pyplot as plt

# Variable to include in the title
year = 2023

# Create figure and axis
fig, ax = plt.subplots()

# Set title using string concatenation
ax.set_title('User Growth in ' + str(year))

# Show plot
plt.show()

This code snippet would display the plot with the title: “User Growth in 2023”.

This method concatenates the string “User Growth in ” with the string representation of the variable year. The title of the plot hence becomes dynamic, reflecting whatever value the year variable holds.

Method 2: String Formatting with format()

The format() string method allows inserting variables into strings with placeholder braces {}. It’s a cleaner alternative to the concatenation approach, provides better readability, and avoids the need for explicit type conversion.

Here’s an example:

# Import Matplotlib's pyplot
import matplotlib.pyplot as plt

# Variable to include in the title
year = 2023

# Create figure and axis
fig, ax = plt.subplots()

# Set title using the format method
ax.set_title('User Growth in {}'.format(year))

# Show plot
plt.show()

This code snippet would display the plot with the title: “User Growth in 2023”.

This snippet utilizes the format() method to insert the year variable into the placeholder within the string. It provides a more readable way to format the title and automatically handles the type casting.

Method 3: f-Strings (Python 3.6+)

Python 3.6 introduced f-strings, a succinct syntax to embed expressions inside string literals, using curly braces {}. It is a very readable and concise way of formatting strings and including variables.

Here’s an example:

# Import Matplotlib's pyplot
import matplotlib.pyplot as plt

# Variable to include in the title
year = 2023

# Create figure and axis
fig, ax = plt.subplots()

# Set title using an f-string
ax.set_title(f'User Growth in {year}')

# Show plot
plt.show()

This code snippet would display the plot with the title: “User Growth in 2023”.

The f-string in f'User Growth in {year}' places the value of year directly in the string’s placeholder. It’s an elegant and expressive way of formatting strings, reducing the need for extra function calls or concatenation.

Method 4: The Percentage Operator

The percentage % operator is an older way for string formatting in Python. It can be used to substitute a set of variables into a string via format specifiers, like %s for string and %d for integers.

Here’s an example:

# Import Matplotlib's pyplot
import matplotlib.pyplot as plt

# Variable to include in the title
year = 2023

# Create figure and axis
fig, ax = plt.subplots()

# Set title using the percentage operator
ax.set_title('User Growth in %d' % year)

# Show plot
plt.show()

This code snippet would display the plot with the title: “User Growth in 2023”.

The title is constructed using the percentage operator to replace the %d specifier with the value of year. This method is less favored in modern Python scripting due to the introduction of more legible string formatting options.

Bonus One-Liner Method 5: Using Template Strings

Python’s string.Template class offers another way for string formatting, which uses a template string and substitution mechanics similar to many template engines. This can be helpful for complex formatting scenarios, including i18n or when creating templates outside of the code.

Here’s an example:

from string import Template
import matplotlib.pyplot as plt

# Variable to include in the title
year = 2023

# Create a template object
title_template = Template('User Growth in $year')

# Create figure and axis
fig, ax = plt.subplots()

# Set title using the substitute method of template object
ax.set_title(title_template.substitute(year=year))

# Show plot
plt.show()

This code snippet would display the plot with the title: “User Growth in 2023”.

In this case, Template‘s .substitute() method is used where $year is a placeholder in the template that is replaced by the provided year variable. Useful for when you have string templates which require minimal changes.

Summary/Discussion

  • Method 1: String Concatenation. Simple and straightforward. Requires explicit type conversion.
  • Method 2: String Formatting with format(). More flexible and readable. Automatically handles type casting.
  • Method 3: f-Strings (Python 3.6+). Expressive and concise. Requires Python 3.6 or newer.
  • Method 4: Percentage Operator. Traditional method. Less readable and accessible than newer methods.
  • Bonus Method 5: Using Template Strings. Offers custom templating options. Useful for templates maintained outside of code or i18n needs.