Summary  
This chapter covers how to add and customize titles in a chart by using a function to set the title text and adjust its location, font size, and color.

General domain of usage  
Data visualization

## Choosing a Title

A good plot includes a clear and informative **title**. Generic titles like "Line plot" or "Scatter plot" lack context and fail to convey the purpose of the visualization. A better example is **"New York Average Monthly Temperatures (2022)"**, which specifies the data content, location, and time period — key details that provide clarity.

The following shows how to set a plot title using `matplotlib`:


import matplotlib.pyplot as plt
programming_languages = ['Python', 'Java', 'C#', 'C++']
shares = [40, 30, 17, 13]
plt.bar(programming_languages, shares, color=['b', 'green', 'red', 'yellow'])
# Setting the plot title
plt.title('Percentage of users of programming languages')
plt.show()

## Title Customization

The title is set using the `plt.title()` function with the title text passed as a **string**. Besides the main `label` parameter, the **font size** can be modified via the `fontsize` argument (default is `10`), and the **font color** can be specified using the `color` parameter. These are the primary options for customizing titles.


Another important parameter is `loc` (location), which can take one of the values: `center` (default), `left`, and `right`. 

Let's now modify the title in our example:

import matplotlib.pyplot as plt

programming_languages = ['Python', 'Java', 'C#', 'C++']
shares = [40, 30, 17, 13]
plt.bar(programming_languages, shares, color=['b', 'green', 'red', 'yellow'])
# Customizing the title appearance
plt.title('Percentage of users of programming languages', loc='left', fontsize=7, color='indigo')
plt.show()

The title is aligned to the **left**, with increased font size and a changed font color. These parameters are usually the main focus when customizing titles.


However, you can always refer to the <a href="https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.title.html" target="_blank"><svg width="1em" height="1em" viewBox="0 0 30 32" fill="none" xmlns="http://www.w3.org/2000/svg"><path fill="none" stroke="#098f67" style="stroke: var(--color1, #098f67)" stroke-linejoin="miter" stroke-linecap="round" stroke-miterlimit="4" stroke-width="2.4156" d="M17.289 17.305v0c-1.754 1.754-4.597 1.754-6.351 0l-7.76-7.759c-1.755-1.755-1.755-4.601 0-6.356v0c1.753-1.753 4.595-1.756 6.351-0.005l6.208 6.187"></path><path fill="none" stroke="#098f67" style="stroke: var(--color1, #098f67)" stroke-linejoin="miter" stroke-linecap="round" stroke-miterlimit="4" stroke-width="2.4156" d="M12.504 13.97v0c1.754-1.754 4.597-1.754 6.351 0l7.762 7.762c1.754 1.754 1.754 4.597 0 6.351v0c-1.754 1.754-4.597 1.754-6.351 0l-5.953-5.953"></path></svg> <code>title()</code> documentation</a>  for more information.




Study More

import unittest
import ast
import inspect
import user_code  # Replace with actual module name if different


def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)


class TestPlotTitle(unittest.TestCase):

    @classmethod
    def setUpClass(cls):
        source = inspect.getsource(user_code)
        cls.tree = ast.parse(source)

        cls.title_calls = [
            node for node in ast.walk(cls.tree)
            if isinstance(node, ast.Call)
            and isinstance(node.func, ast.Attribute)
            and node.func.attr == 'title'
        ]

    def test_title_function_used(self):
        _dynamic_test(
            self,
            len(self.title_calls) > 0,
            "plt.title() is used to set the plot title",
            "Missing call to plt.title()"
        )

    def test_title_text_correct(self):
        try:
            call = self.title_calls[0]
            title_text = call.args[0].s if isinstance(call.args[0], ast.Str) else ""
            _dynamic_test(
                self,
                title_text == 'Boston and Seattle average yearly temperatures',
                "Correct title text is used in plt.title()",
                f"Expected title text 'Boston and Seattle average yearly temperatures', got '{title_text}'"
            )
        except Exception:
            self.fail("Title text argument is missing or incorrectly structured.")

    def test_title_fontsize(self):
        try:
            call = self.title_calls[0]
            fontsize_kw = next((kw for kw in call.keywords if kw.arg == 'fontsize'), None)
            value = fontsize_kw.value.n if fontsize_kw else None
            _dynamic_test(
                self,
                value == 15,
                "Correct fontsize (15) is used in plt.title()",
                f"Expected fontsize=15, got fontsize={value}"
            )
        except Exception:
            self.fail("fontsize argument is missing or incorrectly structured.")

    def test_title_loc(self):
        try:
            call = self.title_calls[0]
            loc_kw = next((kw for kw in call.keywords if kw.arg == 'loc'), None)
            value = loc_kw.value.s if loc_kw else None
            _dynamic_test(
                self,
                value == 'right',
                "Correct location 'right' is used in plt.title()",
                f"Expected loc='right', got loc='{value}'"
            )
        except Exception:
            self.fail("loc argument is missing or incorrectly structured.")


if __name__ == '__main__':
    unittest.main()


test_title.py

Master the foundational skills of data visualization using the object-oriented approach in Matplotlib. Learn to control every aspect of your figures, from axes and legends to colors and styles. Create professional-quality static charts, handle time-series data, and export high-resolution graphics for reports and publications.

Adding Titles

Choosing a Title

Title Customization

解答