How to Create a Chart in Python

Save

Displaying data in the form of charts or graphs in Python requires the use of specialized, external code libraries, and the open-source community offers a programmer a number of good ones to choose from. This demonstration uses the matplotlib library to show how to make a simple chart in Python. Matplotlib has both a broad and deep feature set and is well documented; this makes it a good place to start. If time allows, interested programmers should research other available libraries before committing to any one of them.

Things You'll Need

• Python scripting environment
• Text or code editor
• Matplotlib 2D plotting library

Creating a Chart Using Python

• Import the matplotlib pyplot module into the code file:

import matplotlib.pyplot as plt

• Define variables used for bounding the chart axes and creating data to be plotted:

max_x, max_y, min_x, min_y = 11.0, 11.0*11.0, 0.0, 0.0

• Declare arrays to separately hold x and y values to be plotted:

x_arr = []
y_arr = []

• Fill the arrays with data. Typically you will draw this data from external sources such as files or database queries. Here the code creates sample data, implementing the formula y(x) = x*x:

for i in range(min_x,max_x):
x_arr.append(float(i))
y_arr.append(float(i*i))

• Create a FigureCanvas object using the imported matplotlib pyplot object:

fig = plt.figure()

• Add the graph’s axes to the FigureCanvas by calling the function "add_axes" and passing it an array of values in the form of: left, bottom, width, height. These values define where the graph is placed on the canvas. Values can range from 0.0 to 1.0:

ax = fig.add_axes([0.1, 0.1, 0.8, 0.8])

• Format the graph, adding labels and defining the minimum and maximum values for each axis:

ax.set_xlabel('x data')
ax.set_ylabel('y data')
ax.set_xlim(min_x,max_x)
ax.set_ylim(min_y,max_y)

• Plot the graph by passing in the two arrays containing the x and y values retrieved from the CSV file. Customize the line plot by passing in optional values such as line color (color) or line width (lw):

ax.plot(x_arr,y_arr, color='red', lw=2)

• Call the pyplot module’s show method to display the chart in a window. This functionality and the style of window will depend on the operating system environment and the local installation of matplotlib:

plt.show()

• Store the image by calling savefig to create a bitmap file on disk:

fig.savefig('test.png')

Tips & Warnings

• To create files that the Python interpreter can read, you must use an ascii text or code editor that creates text-only files.
• You can store graph images in many different image formats including: png, pdf, ps and svg.
• Some aspects of the matplotlib library installation and functionality vary on different computer platforms. Read the documentation carefully.
• The library is capable of displaying numerical information in a vast number of ways and can be finely customized.

References

• Photo Credit Hemera Technologies/AbleStock.com/Getty Images
Promoted By Zergnet

Resources

You May Also Like

• How to Create a While Loop in Python

Computers are much better than people at performing repetitive tasks over and over. You may have a large (and sometimes infinite) list...

• How to Make a Graph in MS Excel

Visual aids such as graphs can add interest to an otherwise dry presentation and accelerate comprehension of the data you wish to...

• How to Make a Line Graph in Microsoft Excel

In Excel 2013, a line chart is the best option for graphing one or more sets of data across a chart with...

• How to Create an XY Chart

Often used for analyzing engineering, scientific and statistical data, the XY chart can also help anyone forecast trends by tracking factual data...

• How to Create Matrices in Powerpoint

Microsoft PowerPoint is a presentation tool that is part of the Microsoft Office software suite and allows users to create various charts,...

• How to Code in Python

Python is an interpreted scripting language with simple, readable code intended to be intuitive and even fun to use --- hence its...

• How to Write Computer Code

Learning to write computer code will require the use of a program called Python, which has very easy language to learn. Discover...

Related Searches

Check It Out

Geek Vs Geek: Robot battles, hoverboard drag race, and more

M
Is DIY in your DNA? Become part of our maker community.