Some of the steps needed to setup a development environment includes: Operating system - e.g Linux / Mac Project structure - project structure Virtualenv - isolated installation of the project Pip - a tool for installing and managing Python packages Git - source control Webserver - where we can manage our applications Fabric - automated deployment
Create an empty top-level directory for our new project.
helloflask/ -static/ -css -font -img -js -templates -routes.py Then cd into the directory cd helloflask
Many developers uses virtualenv (virtual environment) on their computer, which is useful when you want to run several applications on the same computer. Virtualenv will manage all dependencies and enables multiple side-by-side installations of Python, one for each project. It doesn't install separate copies of Python, but provides a way to keep different project environments isolated. If we want to run more than one (which is often the case) web application on that host, then you should really install 'Virtualenv'. If you don't use virtualenv , you will have it all globally installed.
Download and Install Virtualenv into a virtual environment
# If you are using Linux/Mac: sudo pip install virtualenv
Setup a new project
Navigate to the directory you want your project in:
$ virtualenv venv # this creates the folder venv $ source venv/bin/activate # start working on your new project (venv)$ pip install Flask # installs Flask
For more information on how to download install virtualenv, see this article.
PIP is a tool for installing and managing Python packages. PIP comes with a command-line interface, which makes installing Python software packages as easy as issuing one command
pip install some-package-name
Users can also easily implement the package's subsequent removal
pip uninstall some-package-name
Pip has a feature to manage full lists of packages and corresponding version numbers through a "requirements" file. This permits the efficient re-creation of an entire group of packages in a separate environment (e.g. another computer) or virtual environment. This can be achieved with a properly formatted requirements.txt file
pip install -r requirements.txt
This makes dependencies easy, you can create a requirements file based on a set of packages installed in your virtual environment.
pip freeze > requirements.txt
When deploying to a server it is important to register which requirements we need. The requirements file can be done automatically using the freeze command for pip. This command will generate a plain text file that contains the names of the required Python packages and their versions, for example Flask==0.9
To do this we freeze the installed packages and store this setup in a requirements.txt file
$ cat requirements.txt Flask==0.9 Jinja2==2.6 Werkzeug==0.8.3
The requirements file can be used to rebuild a virtual environment or to deploy a virtual environment into the machine.
Now that we have a clean Flask environment to work in, we'll create our simple application. The simplest Flask App looks something like this:
Put this code into the file and name it 'hello.py'
from flask import Flask app = Flask(__name__) @app.route('/') def hello(): return 'Hello World!'
Github – Central Repository
Now it's time to create the repository on Github. The purpose of setting up a Github project, is so that we can push files from our local computer to Github and then pull the files from Github to our web server. Create a new Github account and create a new project (helloflask)
Git – Local Computer
By using a versioning system, we can store all our files in a Github repository. The first thing you need to do on your local computer is to install and setup git.
To install git, simple run:
sudo apt-get install git
Put in your username and email into the .gitconfig file (~/.gitconfig)
git config --global user.name "pythonforbeginners" git config --global user.email [email protected]
Since our current directory contains a lof of extra files, we'll want to configure our repository to ignore these files with a .gitignore file: venv *.pyc
Next, we’ll create a new git repository and save our changes.
# Initialize Git in our project directory git init
This creates a git repository in the current directory.
Add all of our files to our initial commit
git add .
Check the status, this will list all files
With the files added to the Git index, we can now commit them to our repo:
$ git commit -m 'Initial commit'
Now we have created a local Git repository for our application (local) files.
Setup Github as the origin
git remote add origin [email protected]:USERNAME/helloflask.git git push -u origin master
Web Server – Host
Now its time to start up the web server and do some configuration. If you want to use Apache as a web server, you can install it like this:
sudo apt-get install apache2
Configure a virtual host (vhost) in /etc/apache2/sites-available/siteX Install virtualenv just like you did on your local computer. Set up the environment for the website, here I use /var/www Cd into that folder and clone the project that you setup on Github, by typing:
git clone [email protected]:USERNAME/helloflask.git
Initialize and activate your virtualenv
virtualenv helloflask cd helloflask source bin/activate
pip install -r requirements.txt
Fabric is used for deployment. You can of course always manually upload the code and restart the web server to reflect the configuration changes. Using fabric in a development environment, where you have multiple servers with multiple people pushing the code multiple times per day, this can be incredible very useful. Fabric can configure the system, execute commands on local/remote server, deploy your application, do rollbacks etc. It does that by using its command-line utility that will run a fabfile containing instructions on how to deploy to a server. A common practice when developing is to use Git to deploy and Fabric to automate it.
pip install fabric
Fabric expects a fabfile named fabfile.py which defines all of the actions we can take. The fabfile.py should be in your project's root directory. I like to use this script that asks the server to pull from the git repository and restart apache. [source]
from fabric.api import * # import fabrics API functions env.hosts = ['[email protected]:22'] # add the remote server information def pushpull(): local('git push') # runs the command on the local environment run('cd /path/to/project/; git pull') # runs the command on the remote environment
#Run it with: $ fab pushpull
For more information on how to use fabric in a development environment, please refer to this article.
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