*29*

You can quickly add circles to a plot in Matplotlib by using the Circle() function, which uses the following syntax:

**matplotlib.patches.Circle(xy, radius=5)**

where:

**xy:**The (x, y) coordinates for the circle**radius:**The radius of the circle. Default is 5.

This tutorial shows several examples of how to use this function in practice:

**Example 1: Create a Single Circle**

The following code shows how to create a single circle on a Matplotlib plot located at (x, y) coordinates (10,10):

import matplotlib.pyplot as plt #set axis limits of plot (x=0 to 20, y=0 to 20) plt.axis([0, 20, 0, 20]) #create circle with (x, y) coordinates at (10, 10) c=plt.Circle((10, 10)) #add circle to plot (gca means "get current axis") plt.gca().add_artist(c)

By default, one axis of a Matplotlib plot typically displays more pixels per data unit. To make a circle appear as a circle instead of an ellipse, you need to use the argument **plt.axis(“equal”)** as follows:

import matplotlib.pyplot as plt #set axis limits of plot (x=0 to 20, y=0 to 20) plt.axis([0, 20, 0, 20]) plt.axis("equal") #create circle with (x, y) coordinates at (10, 10) c=plt.Circle((10, 10)) #add circle to plot (gca means "get current axis") plt.gca().add_artist(c)

**Example 2: C****reate Multiple Circles**

The following code shows how to create multiple circles on a Matplotlib plot:

import matplotlib.pyplot as plt #set axis limits of plot (x=0 to 20, y=0 to 20) plt.axis([0, 20, 0, 20]) plt.axis("equal") #define circles c1=plt.Circle((5, 5), radius=1) c2=plt.Circle((10, 10), radius=2) c3=plt.Circle((15, 13), radius=3) #add circles to plot plt.gca().add_artist(c1) plt.gca().add_artist(c2) plt.gca().add_artist(c3)

**Example 3: Modify Circle Appearance**

You can use the following arguments to modify the appearance of a circle in Matplotlib:

**radius:**Specify radius of circle**color:**Specify color of circle**alpha:**Specify transparency of circle

The following code shows an example of how to use several of these arguments at once:

import matplotlib.pyplot as plt #set axis limits of plot (x=0 to 20, y=0 to 20) plt.axis([0, 20, 0, 20]) plt.axis("equal") #create circle with (x, y) coordinates at (10, 10) c=plt.Circle((10, 10), radius=2, color='red', alpha=.3) #add circle to plot (gca means "get current axis") plt.gca().add_artist(c)

Note that you can also use custom hex color codes to specify the color of circles.