MatplotlibXBy @CodeWithMunnaX
Catalog
Track: Essential Charts
Continuous Shading10 mins

19. Area Charts & fill_between()

`plt.fill_between()` fills the geometric area between two vertical boundary curves $y_1(x)$ and $y_2(x)$, ideal for confidence bands and cumulative volumes.

Mental Model Intuition

Using a highlighter pen to tint the space sandwiched between two contour lines.

Core Concepts & Mechanics

Arguments to `fill_between`Syntax

`plt.fill_between(x, y1, y2, color=..., alpha=...)`. If `y2` is omitted, it defaults to 0 (filling down to baseline).

Always set `alpha=0.2` to `0.4` so underlying grid lines and curves remain visible.
plt.fill_between(x, y1, y2, alpha=0.3)

Common Beginner Mistakes & Pro Fixes

Avoid the top errors and bad plotting practices that trip up new Python developers

Troubleshooting

Quick Lesson Takeaways

  • `plt.fill_between(x, y1, y2)` shades the polygon between two curves.
  • Omit `y2` to fill down to the Y=0 baseline.
  • Always set `alpha < 0.5` for transparency.
Topic 19 • Python IDE
Python 3.12 • Matplotlib
Run Python code to inspect terminal output.

Real-World Datasets (1-Click Switcher)

Switch from abstract numbers to relatable Cricket, Cinema & Business charts

5 Curated Datasets

Hands-on Challenge: Fill Under a Curve

+50 XP

Write Matplotlib code to solve the objective and see your live plot render

Objective Instructions:

Plot `x = [1, 2, 3, 4]` and `y = [2, 6, 4, 8]` with `color='#FFB86B'`, then call `plt.fill_between(x, y, color='#FFB86B', alpha=0.3)`.

Required Keywords:✓ plt.fill_between✓ alpha
Challenge Code Editor
Challenge Output GraphLive Vector Preview
Write code on the left to render live challenge plot
End of Lesson Knowledge Check

Quick Mini Quiz: 2 Concept Questions

Test your understanding to unlock the lesson completion badge

Q1

Which Matplotlib function is used to create a standard continuous 2D line plot?

Q2

What must you call after specifying label='...' so that the legend actually appears on the canvas?

0 of 2 answered