Home > Articles > Programming > Python

Python and Your Phone: Let’s Talk About Kivy

  • Print
  • + Share This
With the popularity of smartphones and tablets, everyone wants in on the app-programming action. Thanks to a new library, Python programmers can get on board and program apps using Kivy. After confirming you have the prerequisite base knowledge, this article introduces the key Kivy features and then shows how to handle layout in Kivy and explore some existing examples.
Like this article? We recommend

At least once a week, someone is in the Python IRC channel on Freenode asking a very specific question: How can they use Python to make an app for their Android or iOS phone?

For a long time, the answer was “You don’t.” In order to write an app for Android or iOS, you had to learn either Java or Objective-C, or you had to use a third-party application that relied on a GUI, HTML, and Javascript to create applications. Python doesn’t run natively on any of the major mobile platforms, so there was no uploading a .py file and simply running it. A few libraries covered Android, but left out iOS.

Python still isn’t included with any of the platforms, but a library has come along that has made it possible to use Python to create applications that run on iOS, Android, and even on desktops (Linux, Windows, and OSX). That library is Kivy.

What is Kivy?

Kivy is a library that allows you to use Python to create applications for mobile devices and desktops. It takes your code and creates applications from your logic. Then, with each app and APK, it includes a nearly complete installation of Python.

Write Once, Deploy to Many

The biggest feature of Kivy is the ability to write code once and deploy that code to many platforms. Everyone with a smartphone has felt the pain of seeing an awesome app come out for one line of phones, but never materialize for their particular phone.

Even more common is when a useful app comes out, but there’s no desktop equivalent. Not everyone has access to a smartphone, or wants a certain app with them all the time. There are quite a few games I wish existed on my computer, where I could have keyboard and mouse control, as well as some productivity apps, like task managers or certain alarm tools.

With Kivy, you don’t need a developer for each platform. One developer can create for all of them, and then push a separately packaged application to each app store.

Key Kivy Features

Kivy goes beyond a framework for creating simple apps for your phone or desktop. It can interface with the phone’s hardware and do advanced rendering. It has access to rendering engines. It can do so much more than a simple web app could do.

  • Camera: There are built in adapters for smartphone cameras. This is one of the first requirements that will have me jumping over to creating a native app, rather than creating a responsive website. Though there are, in theory, some HTML5 inputs for cameras, the coverage for this in browsers is spotty at best.
  • Video: Kivy includes modules for reading and playing videos. True, this can be done through a web app, but the experience can sometimes be shaky. Older phones might try to play the video without taking up the whole screen, or the memory usage might be higher than it should be.
  • Multitouch and gestures: Kivy has a robust module for input, allowing for multitouch and gestures.
  • Visual effects and OpenGL: Because Kivy has access to OpenGL, it can perform a large array of visual effects and do quite a bit of rendering. Kivy also uses PyGame, so creating games becomes much easier (though you do have to rewrite existing PyGame code for Kivy). PyGame comes with modules for drawing shapes, rendering, dealing with colors, and playing music (as well as blowing things up, naturally).
  • Asynchronous network requests: One important feature of any native app, at least for people like me who travel in and out of network areas, is the ability to finish requests when a network is available. I like being able to work on my phone while in a tunnel, then have it sync my work to the cloud when I hit a station.
  • UI features: Kivy comes with a number of widgets and controls that are beautifully designed. This can be a real benefit to your project if you’re trying to prototype quickly, and don’t yet have access to a designer.

Example program

It doesn’t take very many lines of code to create a Kivy program. Here’s a sample ‘Hello, World’ application from the documentation:

import kivy
kivy.require('1.0.6') # replace with your current kivy version !

from kivy.app import App
from kivy.uix.button import Button

class MyApp(App):
    def build(self):
        return Button(text='Hello World')

if __name__ == '__main__':
    MyApp().run()

What You Need to Know to Successfully Develop Kivy Apps

You should have a pretty solid grasp on Python. Learning Python while trying to learn Kivy might end up confusing the beginner. You don’t need to be an expert Python programmer, but you should be comfortable delving into docs and using APIs.

You should also be familiar with MVC patterns. You can write a Kivy program without them, but it might drive you slowly mad as the program grows.

Finally, while you don’t need to know how to program on Android or iOS, you should know some of the high-level concepts, like what devices are common with each OS, and how to run emulators. A run through a high-level tutorial should be enough to get you comfortable with what’s to come. You should also take some time to get comfortable with some of the APIs that Kivy doesn’t cover, like GPS or notifications.

If you already program on Android or iOS, a bit of a perspective shift might be needed. Kivy creates single-window apps. There are ways to simulate multiple windows, but this can be confusing to some when they first move over.

Layout in Kivy

Kivy comes with a special language for defining layout. This allows you to keep your logic and presentation separate. Kv (the layout language) isn’t complex, but you should review the documentation briefly before diving in.

A Kv file looks something like this:

<ClassName>:    
    LayoutType:
        WidgetType:
            pos: self.center_x - 5, 0
            size: 10, self.height
            
    LayoutType2:
        font_size: 70  
        center_x: root.width / 4
        top: root.top - 50
        text: "0"

So WidgetType is within LayoutType, and LayoutType2 is right after LayoutType. These are all stored in a view called ViewName, which can be reused throughout the application by different views. As for the values to the left of the colon, those are Python statements. They might be as simple as a single value, or they might be a calculation of some kind.

There are a number of layouts and widgets available out of the box:

  •     Accordion: Expands or collapses items through touch or clicks
  •     ActionBar and ActionItems: Collects items you might want to give the user quick access to.
  •     BoxLayout: Arranges children in a box, horizontally or vertically.
  •     Bubble: Brings up a bubble with possible actions or information (like what is at a location, or giving the option to copy or paste information)
  •     Button: Just what it sounds like! A button!
  •     Carousel: Allows the user to swipe between slides
  •     And many more!

Examples in the Wild

Same code is all well and good, but where is Kivy being used in production, by actual companies?

Bargenius is an app made for single-use tablets, specializing in what foods pair with what drinks. Rather than give a visitor a paper menu, they can be given a tablet that offers additional details about the food being offered, and suggest what drinks might go with their selection.

Particle Panda HD is useful for exploring what Kivy can do with its graphics libraries. With it, the user can create particle effects that can then be exported, so they can be used in other applications. This application is completely free, so make sure to check it out if you’re interested in rendering graphics or high-end effects.

ProcessCraft is a business application geared towards individuals who need to model complex business data, but don’t want to train staff to use complex notation.

Finally, you can look at the source code of three games written in Kivy and submitted for a 2012 contest: Deflectouch uses Kivy’s multitouch capabilities, FishLife explores industrial waste and its impact on sea life, and memoryKivy is a simple memory game.

For a more extensive list of Kivy examples, check out the official list on Github.

Do I Have to Pay Them?

You do not! Kivy is open source (MIT licensed), and does not require any payment, even if you end up making an app that generates money through sales or ads. They don’t even require a link to their module, and you can feel free to fork them on GitHub.

Just because you don’t have to pay Kivy doesn’t mean a piper doesn’t need to be paid. Developer licenses still need to be purchased for each market where you want to publish your app. Here are the current rates as of November 2013:

  • iOS/OSX: $99 a year (unlimited apps)
  • Android (Play): $25 lifetime (unlimited apps)
  • Android (Amazon): Free (unlimited apps)
  • Windows store: $19 a year (unlimited apps)You should also note that, just because you made an app doesn’t mean it will get accepted. For each store, apps are reviewed (though some of the stores are more thorough than others), and rejection is always a possibility.

Where You Can Learn More

Obviously, the best place to start is kivy.org! There, they have documentation, example projects, and tutorials.

Ben Rousch did an excellent tutorial at PyOhio, showing off what Kivy can do as well as building an app live. You can watch that video on PyVideo.org. If you’re not interested in the demos, go ahead and skip to 14:00. I was next door, and I can attest to the fact that it was standing room only, and one of the most talked about tutorials of the conference. 

On Android, I recommend installing the Kivy Showcase app. It will give you an idea what Kivy is capable of, and provides a handy reference for UI elements. Showcase is also available for the desktop by downloading the Kivy source and looking in the examples folder.

Kivy.org also hosts a feed of all of recent blog posts about Kivy at http://kivy.org/planet/. If you’d rather talk to some of the developers and users, you may want to check out their IRC channel, #kivy, on Freenode.

I hope that if you do decide to make an app with Kivy, you drop by to show it off! Kivy is building a friendly and eager community around its framework, and we would love to see what you do with it!

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020