[Term Entry] Python matplotlib - pyplot: fill_between()

content/matplotlib/concepts/pyplot/terms/fill-between/fill-between.md

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+---
+Title: 'fill_between()'
+Description: 'Fills the area between two curves or between a curve and a baseline in a plot.'
+Subjects:
+  - 'Data Science'
+  - 'Data Visualization'
+Tags:
+  - 'Graphs'
+  - 'Libraries'
+  - 'Matplotlib'
+  - 'Methods'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/data-science'
+---
+
+The **`fill_between()`** function in Matplotlib's `pyplot` module creates a shaded region between two curves or between a curve and a baseline. It is commonly used to visualize ranges, confidence intervals, thresholds, and differences between datasets.
+
+## Syntax
+
+```pseudo
+matplotlib.pyplot.fill_between(x, y1, y2=0, where=None, **kwargs)
+```
+
+**Parameters:**
+
+- `x`: Sequence of x-coordinates.
+- `y1`: First set of y-values.
+- `y2` (optional): Second set of y-values. Defaults to `0`, creating a fill between the curve and the x-axis.
+- `where` (optional): A boolean mask that controls where to fill.
+- `**kwargs`: Additional styling options such as `color`, `alpha`, or `label`.
+
+**Return value:**
+
+Returns a `PolyCollection` object that represents the shaded region.
+
+## Example
+
+The example below shows how to fill the area between a curve and the x-axis:
+
+```py
+import matplotlib.pyplot as plt
+import numpy as np
+
+x = np.linspace(0, 10, 200)
+y = np.sin(x)
+
+plt.plot(x, y)
+plt.fill_between(x, y, 0, alpha=0.3)
+
+plt.title("Filled Area Under Sine Curve")
+plt.show()
+```
+
+The output of this code is:
+
+![A sine wave plot with a shaded region under the curve created using fill_between(), showing area fill and transparency.](https://raw.githubusercontent.com/Codecademy/docs/main/media/Figure_1.png)
+
+## Example
+
+This example fills the area between two curves:
+
+```py
+import matplotlib.pyplot as plt
+import numpy as np
+
+x = np.linspace(0, 5, 100)
+y1 = x
+y2 = x**2
+
+plt.plot(x, y1, label="y = x")
+plt.plot(x, y2, label="y = x^2")
+
+plt.fill_between(x, y1, y2, alpha=0.3)
+
+plt.legend()
+plt.show()
+```
+
+![A plot of y = x and y = x² with the area between the two curves shaded using fill_between(), illustrating curve comparison and filled regions.](https://raw.githubusercontent.com/Codecademy/docs/main/media/Figure_2.png)