Practical application development using Python

Although the Python language is very versatile, it is still a bit wrong to use it to develop apps. Therefore, apps developed with Python should be used as coding exercises or for self-entertainment. The current modules in this area are not particularly mature and have many bugs. In short, I advise you not to jump into it lightly.

Preparation

Using Python to develop apps requires the use of a module of Python – kivy. kivy is an open source, cross-platform Python development framework for development Use innovative apps. In short, this is a Python desktop program development framework (similar to wxpython and other modules). The powerful thing is that kivy supports linux, mac, windows, android, and ios platforms. This is why this module is needed to develop apps.

Although kivy is cross-platform, if you want to use Python code on different platforms, you also need to package the Python code into an executable program for the corresponding platform. Fortunately, there is a packaging tool under the kivy project Project – buildozer, this is the officially recommended packaging tool because it is relatively simple and has a high degree of automation. Other projects such as Python-for-android can also play a similar role and will not be introduced here.

Building kivy development environment

You need to install the kivy development environment on your PC. Here is a demonstration of the installation process under mac and linux.

install kivy for mac

Install some dependent packages:

brew install pkg-config sdl2 sdl2_image sdl2_ttf sdl2_mixer gstreamer

Install cython and kivy:

pip install cython==0.25
pip install kivy

If an error is reported when installing kivy, use the following method to install kivy:

git clone https://github.com/kivy/kivy
python setup.py install

Post-installation test:

$python
Python 2.7.10 (default, Jul 15 2017, 17:16:57)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> import kivy
[INFO ] [Logger] Record log in /Users/didi/.kivy/logs/kivy_18-05-08_4.txt
[INFO ] [Kivy] v1.10.1.dev0, git-5f6c66e, 20180507
[INFO ] [Python] v2.7.10 (default, Jul 15 2017, 17:16:57)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)]

Note: If there is no error when importing the kivy module, it means the installation is successful.

install kivy for centos7

First install the dependencies:

yum install 
make 
mercurial 
automake 
gcc 
gcc-c++ 
SDL_ttf-devel 
SDL_mixer-devel 
khrplatform-devel 
mesa-libGLES 
mesa-libGLES-devel 
gstreamer-plugins-good 
gstreamer 
gstreamer-python 
mtdev-devel 
python-devel 
python-pip 
java-devel

Install cython and kivy:

pip install Cython==0.20
pip install kivy

centos installation kivy reference: https://kivy.org/docs/installation/installation-linux.html#using-software-packages

Note: Other ways to install kivy can be found at: https://kivy.org/ #download (need to circumvent the wall)

Develop the first Python app with kivy

After installing kivy, you can develop the app program. Here is a demonstration of the hello-world program. , the more complex usage of kivy is not the focus of this article, and will be introduced later.

Create a main.py file and write:

#! -*- coding:utf-8 -*-
from kivy.app import App
class HelloApp(App):
pass
if __name__ == '__main__':
HelloApp().run()

Create a hello.kv file and write:

Label:
text: 'Hello, World! I am nMask'

Simple Note: main.py is the entry function and defines a HelloApp class, which inherits kivy.app; the hello.kv file is a kivy program, which is equivalent to defining the interface style, etc. The naming rule of this file is that the class name is in lowercase and app is removed.

Run the first Python app

python main.py

Run result:

##Install the buildozer tool

Through the above coding, I created my first python app program. This program can run directly on mac, linux, and windows platforms. So how do I make it run on Android or Apple phones? Woolen cloth? We know that to run on Android, it needs to be packaged into an apk installation program, so we need to use the buildozer tool mentioned earlier. (The buildozer tool can package kivy programs and supports android, ios, etc.). The installation process of buildozer is relatively simple. ：

pip install buildozer

Use the buildozer tool to package the kivy program into an apk

Run it in the python project directory:

buildozer init

If the operation is successful, it will Create a configuration file buildozer.spec. You can change the name of the app by modifying the configuration file, and then run:

buildozer android debug deploy run

Running the above command will generate a cross-platform installation package, applicable to Android, ios, etc. , if used for Android, use the python-for-android project.

When you run the above command for the first time, necessary files such as Android sdk will be automatically downloaded in the system, as shown below. (The process requires overcoming the firewall, and there are many dependencies that need to be downloaded)

Note: Here we only demonstrate packaging into apk files, you can study it yourself on the iso platform, refer to the documentation : https://github.com/kivy/buildozer.

python apk program test

If the above steps are successful, an apk file should be generated in the bin directory under the project directory, similar to the following:

Then download the apk to your Android phone and install it. The test results are as follows:

Open app

buildozer使用说明

Usage:
buildozer [--profile <name>] [--verbose] [target] <command>...
buildozer --version
Available targets:
androidAndroid target, based on python-for-android project
iosiOS target, based on kivy-ios project
android_oldAndroid target, based on python-for-android project (old toolchain)
Global commands (without target):
distcleanClean the whole Buildozer environment.
help Show the Buildozer help.
init Create a initial buildozer.spec in the current directory
serveServe the bin directory via SimpleHTTPServer
setdefault Set the default command to run when no arguments are given
versionShow the Buildozer version
Target commands:
cleanClean the target environment
update Update the target dependencies
debugBuild the application in debug mode
releaseBuild the application in release mode
deploy Deploy the application on the device
runRun the application on the device
serveServe the bin directory via SimpleHTTPServer
Target "android_old" commands:
adbRun adb from the Android SDK. Args must come after --, or
use --alias to make an alias
logcat Show the log from the device
Target "ios" commands:
list_identitiesList the available identities to use for signing.
xcodeOpen the xcode project.
Target "android" commands:
adbRun adb from the Android SDK. Args must come after --, or
use --alias to make an alias
logcat Show the log from the device
p4aRun p4a commands. Args must come after --, or use --alias
to make an alias

buildozer打包过程中的坑点

如果在打包过程中遇到报错，可以修改buildozer.spec配置文件中的log_level为2，然后重新运行，可以看具体的错误信息。

报错：You might have missed to install 32bits libs

这个错是我在centos7上运行时报的错，大意是系统缺少了某些32位的依赖文件。

解决方案：

yum -y install --skip-broken glibc.i686 arts.i686 audiofile.i686 bzip2-libs.i686 cairo.i686 cyrus-sasl-lib.i686 dbus-libs.i686 directfb.i686 esound-libs.i686 fltk.i686 freeglut.i686 gtk2.i686 hal-libs.i686 imlib.i686 lcms-libs.i686 lesstif.i686 libacl.i686 libao.i686 libattr.i686 libcap.i686 libdrm.i686 libexif.i686 libgnomecanvas.i686 libICE.i686 libieee1284.i686 libsigc++20.i686 libSM.i686 libtool-ltdl.i686 libusb.i686 libwmf.i686 libwmf-lite.i686 libX11.i686 libXau.i686 libXaw.i686 libXcomposite.i686 libXdamage.i686 libXdmcp.i686 libXext.i686 libXfixes.i686 libxkbfile.i686 libxml2.i686 libXmu.i686 libXp.i686 libXpm.i686 libXScrnSaver.i686 libxslt.i686 libXt.i686 libXtst.i686 libXv.i686 libXxf86vm.i686 lzo.i686 mesa-libGL.i686 mesa-libGLU.i686 nas-libs.i686 nss_ldap.i686 cdk.i686 openldap.i686 pam.i686 popt.i686 pulseaudio-libs.i686 sane-backends-libs-gphoto2.i686 sane-backends-libs.i686 SDL.i686 svgalib.i686 unixODBC.i686 zlib.i686 compat-expat1.i686 compat-libstdc++-33.i686 openal-soft.i686 alsa-oss-libs.i686 redhat-lsb.i686 alsa-plugins-pulseaudio.i686 alsa-plugins-oss.i686 alsa-lib.i686 nspluginwrapper.i686 libXv.i686 libXScrnSaver.i686 qt.i686 qt-x11.i686 pulseaudio-libs.i686 pulseaudio-libs-glib2.i686 alsa-plugins-pulseaudio.i686 python-matplotli

参考：https://ask.fedoraproject.org/en/question/9556/how-do-i-install-32bit-libraries-on-a-64-bit-fedora/

报错：Error compiling Cython file

错误大意为cython文件出错，可能是cython模块没有安装，或者版本有问题。解决方案：

pip install cython==0.25

报错：IOError: [Errno 2] No such file or directory….. 这是在打包的最后一步，将apk文件copy到项目bin目录下时报的错，是buildozer的一个bug。

解决方案：

修改/usr/local/lib/python2.7/dist-packages/buildozer/tagets/android.py文件：

在文件开头导入:

from distutils.version import LooseVersion

将786行:XXX found how the apk name is really built from the title这一行以下的代码替换为：

__sdk_dir = self.android_sdk_dir
build_tools_versions = os.listdir(join(__sdk_dir, 'build-tools'))
build_tools_versions = sorted(build_tools_versions, key=LooseVersion)
build_tools_version = build_tools_versions[-1]
gradle_files = ["build.gradle", "gradle", "gradlew"]
is_gradle_build = any((exists(join(dist_dir, x)) for x in gradle_files)) and build_tools_version >= ’25.0'

buildozer虚拟机

kivy官方推出了一个buildozer虚拟机镜像，已经安装好了buildozer以及一些依赖文件，为buildozer打包测试提供平台。由于之前我在mac上利用buildozer打包一直报错，后来换成centos也依然没有成功，因此便下载了此虚拟机，测试效果如下：

虚拟机下载地址：http://txzone.net/files/torrents/kivy-buildozer-vm-2.0.zip

说明：对于无法解决依赖问题的朋友，可以使用此虚拟机进行程序打包，开发环境还是推荐用自己的本机。

kivy开发实例

因为本文重点在于介绍如何利用kivy+buildozer开发一款python app，因此对于kivy的开发过程，以及app功能进行了最简化。

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