What is matplotlib?

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Matplotlib is a Python library used to create charts and graphs. The concepts you will learn include:

• Creating a line graph from data
• Changing the appearance of the line
• Zooming in on different parts of the axis
• Putting labels on titles and axes
• Creating a more complex figure layout
• Adding legends to graphs
• Changing tick labels and positions
• Saving what you've made

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Basic Line Plot

Line graphs are helpful for visualizing how a variable changes over time. Some possible data that would be displayed with a line graph:

• average prices of gasoline over the past decade
• weight of an individual over the past couple of months
• average temperature along a line of longitude over different latitudes

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Using matplotlib methods, the following code will create a simple line graph using .plot() and displaying it using .show():

x_values = [0, 1, 2, 3, 4]
y_values = [0, 9, 4, 1, 16]
plt.plot(x_values, y_values)
plt.show()

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• x_values is a variable holding a list of x-values for each point on our line graph
• y_values is a variable holding a list of y-values for each point on our line graph
• plt is the name we have given to the matplotlib module we have imported at the top of the code
• plt.plot(x_values, y_values) will create the line graph
• plt.show() will actually display the graph

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1. We are going to make a simple graph representing someone's spending on lunch over the past week. First, define two lists, days and money_spent.
2. Plot days on x-axis and money_spent on the y-axis using plt.plot().
3. Show the plot using plt.show().

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We can also have multiple line plots displayed on the same set of axes. This can be very useful if we want to compare two datasets with the same scale and axis categories. Matplotlib will automatically place the two lines on the same axes and give them different colors if you call plt.plot() twice.

Let's look at the graph we made in the last exercise to track lunch spending, where days is on the x-axis and spending (money_spent) is on the y-axis and add a friend's spending for comparison:

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We then get two lines on the same plot. By default, the first line is always blue, and the second line is always orange.

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1. We have defined lists called time, revenue, and costs. Plot revenue vs time. Plot cost vs time on the same plot. Show the plot using plt.show().