Introduction to Matplotlib

Matplotlib is a Python library for creating charts and visualizations — it turns raw lists of numbers into clear line plots, bar charts, histograms, and more that you can save, share, and explore.

Learn Introduction to Matplotlib in our free Matplotlib course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick…

Part of the free Matplotlib course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

In this first lesson you'll install Matplotlib, import it the standard way, and render your very first chart.

What You'll Learn in This Lesson

1 What Is Matplotlib?

Matplotlib is the most widely used plotting library in Python. It lets you transform data — numbers in lists, arrays, or DataFrames — into visual charts that humans can actually understand at a glance.

Almost every Python data tool — pandas, seaborn, scikit-learn — builds on top of Matplotlib, so learning it gives you a foundation for the entire data-visualization world.

2 Installing and Importing Matplotlib

Matplotlib isn't built into Python, so install it once from your terminal:

Then, in your Python file, import the pyplot module. Almost everyone uses the alias plt :

What you'll see: a window opens with a blue line rising from 100 up to 240, with the five month numbers along the bottom (x-axis) and the sales values up the side (y-axis). That's a complete chart in just three lines of real code.

3 Showing vs. Saving a Chart

There are two ways to get your chart out of Python: plt.show() opens an interactive window, while plt.savefig() writes the chart to an image file on disk.

What you'll see: a smooth upward curve (a parabola, because y is x squared). A file named squares.png is also written to your working folder — open it and you'll see the exact same chart as an image.

🎯 Your Turn: Fill in the Blanks

Replace each ___ to plot a small dataset and display it.

📋 Common Errors & Quick Reference

❌ ModuleNotFoundError: No module named 'matplotlib'

You haven't installed it. Run pip install matplotlib in your terminal first.

You forgot plt.show() . In a plain script the window only opens when you call it.

Call

What It Does

import matplotlib.pyplot as plt

Standard import

plt.plot(x, y)

Draw a line plot

plt.show()

Open the chart window

plt.savefig("name.png")

Save chart to a file

🏆 Mini Challenge: Temperature Trend

Plot a week of daily temperatures and save the chart to a file.

❓ Frequently Asked Questions

Lesson 1 complete — you've drawn your first chart!

You installed Matplotlib, imported pyplot the standard way, and rendered and saved a real chart with just a few lines of code.

🚀 Up next: The Figure & Axes — understand the two objects that hold every plot.

Practice quiz

What kind of library is Matplotlib?

  • A web framework
  • A plotting and visualization library
  • A database driver
  • A unit-testing tool

Answer: A plotting and visualization library. Matplotlib is Python's most widely used library for creating charts and visualizations.

Which command installs Matplotlib?

  • import matplotlib
  • python matplotlib
  • pip install matplotlib
  • plt install

Answer: pip install matplotlib. Matplotlib is not in the standard library, so you install it with pip install matplotlib.

What is the standard import line for pyplot?

  • import matplotlib.pyplot as plt
  • import pyplot as plt
  • from matplotlib import plt
  • import matplotlib as plt

Answer: import matplotlib.pyplot as plt. The conventional alias is plt: import matplotlib.pyplot as plt.

Which call draws a line connecting points from two lists?

  • plt.draw(x, y)
  • plt.line(x, y)
  • plt.show(x, y)
  • plt.plot(x, y)

Answer: plt.plot(x, y). plt.plot(x, y) connects the (x, y) points with a line.

Which call opens an interactive window showing the chart?

  • plt.show()
  • plt.display()
  • plt.render()
  • plt.open()

Answer: plt.show(). plt.show() opens the figure window in a plain script.

Which call writes the chart to an image file?

  • plt.export()
  • plt.write()
  • plt.savefig('chart.png')
  • plt.tofile()

Answer: plt.savefig('chart.png'). plt.savefig('name.png') saves the figure to disk as an image.

Why should savefig() be called before show()?

  • savefig is faster than show
  • show requires a filename
  • Order does not matter at all
  • show() clears the figure, so a later savefig would be blank

Answer: show() clears the figure, so a later savefig would be blank. After show() closes the window the figure is cleared, so call savefig() first.

If you call plt.plot but see nothing in a script, what is the likely cause?

  • You used the wrong color
  • You forgot plt.show()
  • The data was too small
  • You must call plt.draw twice

Answer: You forgot plt.show(). In a plain script the window only appears when you call plt.show().

What error means Matplotlib is not installed?

  • SyntaxError
  • ValueError
  • ModuleNotFoundError: No module named 'matplotlib'
  • ImportWarning

Answer: ModuleNotFoundError: No module named 'matplotlib'. ModuleNotFoundError appears when the package has not been installed with pip.

Which tools commonly build on top of Matplotlib?

  • pandas, seaborn, and scikit-learn
  • numpy only
  • the os and sys modules
  • requests and flask

Answer: pandas, seaborn, and scikit-learn. Many data tools like pandas, seaborn, and scikit-learn build their plotting on Matplotlib.

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