Using Python to develop app, let’s see how it works.

Time:2021-2-27

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This article is from Tencent cloud by Python sophomore在这里插入图片描述

Recently, I thought of trying to develop an app with Python. After Google searched for some time, it found that there was a way to find it. At present, there were some relatively mature modules, so I started to fight. In the process, I found that there were many pitfalls. Fortunately, I finally relied on Google to solve them, so I made a note.

What I said before

Although the python language is very versatile, it seems a bit wrong to use it to develop apps. Therefore, apps developed with Python should be used as coding exercises or for self entertainment. In addition, the current modules in this field are not particularly mature, and there are many bugs. In a word, we advise you not to enter lightly.

preparation

Using Python to develop app needs to use a module of Python – Kivy. Kivy is an open source, cross platform Python development framework for developing innovative applications. 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, which 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 need to package the Python code into the executable program of the corresponding platform. Fortunately, under Kivy project, there is a packaging tool project, buildozer, which is the official recommended packaging tool, because it is relatively simple and highly automated. Other projects, such as Python for Android, can also play a similar role The function is not introduced here.

Build Kivy development environment

Kivy development environment needs to be installed on 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, install Kivy in the following way:

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 in importing Kivy module, the installation is successful.

install kivy for centos7

 

Install dependencies first:

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 Kivy installation methods can be moved: https://kivy.org/#download (need to go over the wall)

Developing the first Python app with Kivy

After Kivy is installed, 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, but will be introduced later.

  1. Create a main.py File, write:
#! -*- coding:utf-8 -*-
from kivy.app import App
class HelloApp(App):
pass
if __name__ == '__main__':
HelloApp().run()

 

2) Create a hello.kv File, write:

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

 

Brief description: main.py Is an entry function that defines a helloapp class that inherits kivy.app ; hello.kv The file is a Kivy program, which is equivalent to defining the interface style and so on. The naming rule of the file is that the class name is lowercase and the app is removed.

Run the first Python app

python main.py

 

Results of operation:

在这里插入图片描述

Install the buildozer tool

Through the above coding, I created my first Python app program, which can run directly on MAC, Linux and windows platforms. So how can I make it run on Android or Apple Mobile? We know that to run on Android, we need to package it as an APK installation program, so we need to use the buildozer tool mentioned above (buildozer tool can package Kivy programs, support Android, IOS, etc.). The installation process of buildozer is relatively simple

pip install buildozer

 

Using buildozer to package Kivy program into apk
Run in the python project directory:

buildozer init

 

Running successfully 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, which can be used for Android, IOS, etc. if it is used for Android, it is to use the python for Android project.

When you run the above command for the first time, you will automatically download Android SDK and other necessary files in the system, as shown in the figure below. (the process needs to go over the wall, and there are many dependencies that need to be downloaded)

在这里插入图片描述
Note: here, we only demonstrate how to package it into APK file. We can study the ISO platform by ourselves. Please refer to the following documents: https://github.com/kivy/buildozer .

Testing of Python APK program

If the above steps are successful, an APK file should be generated in the bin directory of the project directory, similar to the following:
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Then download the APK to the Android mobile phone and install it. The test results are as follows:

在这里插入图片描述
Open app
在这里插入图片描述
How to use buildozer

Usage:
buildozer [--profile ] [--verbose] [target] ...
buildozer --version
Available targets:
android        Android target, based on python-for-android project
ios            iOS target, based on kivy-ios project
android_old    Android target, based on python-for-android project (old toolchain)
Global commands (without target):
distclean          Clean the whole Buildozer environment.
help               Show the Buildozer help.
init               Create a initial buildozer.spec in the current directory
serve              Serve the bin directory via SimpleHTTPServer
setdefault         Set the default command to run when no arguments are given
version            Show the Buildozer version
Target commands:
clean      Clean the target environment
update     Update the target dependencies
debug      Build the application in debug mode
release    Build the application in release mode
deploy     Deploy the application on the device
run        Run the application on the device
serve      Serve the bin directory via SimpleHTTPServer
Target "android_old" commands:
adb                Run 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_identities    List the available identities to use for signing.
xcode              Open the xcode project.
Target "android" commands:
adb                Run adb from the Android SDK. Args must come after --, or
use --alias to make an alias
logcat             Show the log from the device
p4a                Run p4a commands. Args must come after --, or use --alias
to make an alias

 

Pits in the packaging process of buildozer

If an error is reported during packaging, you can modify it buildozer.spec Log in configuration file_ Level to 2, and then re run, you can see the specific error message.

You might have missed to install 32bits LIBS
This is a mistake I made when I ran the times on CentOS 7, to the effect that the system is missing some 32-bit dependent files.
Solution:

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

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

Error completing Python file
The main idea of the error is that there is an error in the cyton file. It may be that the cyton module is not installed, or there is a problem with the version.
Solution:

pip install cython==0.25

 

Error: ioerror: [errno 2] no such file or directory
This is the last step in packaging. It’s a bug in buildozer to copy the APK file to the bin directory of the project.

Solution:

Modify / usr / local / lib / python2.7/dist-packages/buildozer/tags/ android.py File:

(1) Import at the beginning of the file:

from distutils.version import LooseVersion

 

(2) Replace the 786 line: XXX found how the APK name is really built from the title with the following code:

__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 virtual machine

Kivy officially launched a virtual machine image of buildozer. Buildozer and some dependent files have been installed to provide a platform for buildozer packaging and testing. Before, I used buildozer to package on MAC and reported errors all the time. Later, I still failed to switch to CentOS, so I downloaded this virtual machine. The test results are as follows:
在这里插入图片描述
Virtual machine download address: http://txzone.net/files/torrents/kivy-buildozer-vm-2.0.zip

Note: for those who can’t solve the dependency problem, you can use this virtual machine for program packaging, and the development environment is still recommended to use your own machine.

Kivy development example

Because this article focuses on how to use Kivy + buildozer to develop a python app, so the development process of Kivy and the function of app are simplified. If you want to learn how to develop more complex apps, please refer to: https://muxuezi.github.io/posts/kivy-perface.html#

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