pecan/docs/source/quick_start.rst

Quick Start

Let's create a small sample project with Pecan.

Note

This guide does not cover the installation of Pecan. If you need instructions for installing Pecan, go to installation.

Base Application Template

A basic template for getting started is included with Pecan. From your shell, type:

$ pecan create

The above command will prompt you for a project name. I chose test_project, but you can also provided as an argument at the end of the example command above, like:

$ pecan create test_project

Go ahead and change into your newly created project directory:

$ cd test_project
$ ls

This is how the layout of your new project should look:

├── MANIFEST.in
├── config.py
├── public
│   ├── css
│   │   └── style.css
│   └── javascript
│       └── shared.js
├── setup.cfg
├── setup.py
└── test_project
    ├── __init__.py
    ├── app.py
    ├── controllers
    │   ├── __init__.py
    │   └── root.py
    ├── model
    │   └── __init__.py
    ├── templates
    │   ├── error.html
    │   ├── index.html
    │   ├── layout.html
    │   └── success.html
    └── tests
        ├── __init__.py
        ├── test_config.py
        └── test_root.py

The amount of files and directories may vary, but the above structure should give you an idea of what you should expect.

A few things have been created for you, so let's review them one by one:

• public: All your static files (like CSS and Javascript) live here. If you have any images (this example app doesn't) they would live here too.

The remaining directories encompass your models, controllers and templates, and tests:

• test_project/controllers: The container directory for your controller files.
• test_project/templates: All your templates go in here.
• test_project/model: Container for your model files.
• test_project/tests: All of the tests for your application.

To avoid unneeded dependencies and to remain as flexible as possible, Pecan doesn't impose any database or ORM (Object Relational Mapper) out of the box. You may notice that model/__init__.py is mostly empty. You may wish to add code here to define tables, ORM definitions, and parse bindings from your configuration file.

Note

The base project contains some ready-to-run tests. Try running py.test (the recommended test runner for Pecan) and watch them pass!

Running the application

Before starting up your Pecan app, you'll need a configuration file. The base project template should have created one for you already, config.py.

This file already contains the necessary information to run a Pecan app, like ports, static paths and so forth.

If you just run pecan serve, passing config.py as an argument for configuration, it will bring up the development server and serve the app:

$ pecan serve config.py 
Starting subprocess with file monitor
Starting server in PID 000.
serving on 0.0.0.0:8080 view at http://127.0.0.1:8080

The location for the config file and the argument itself are very flexible - you can pass an absolute or relative path to the file.

Simple Configuration

For ease of use, Pecan configuration files are pure Python.

This is how your default configuration file should look:

from test_project.controllers.root import RootController

import test_project

# Server Specific Configurations
server = {
    'port' : '8080',
    'host' : '0.0.0.0'
}

# Pecan Application Configurations
app = {
    'root' : RootController(),
    'modules' : [test_project],
    'static_root' : '%(confdir)s/public', 
    'template_path' : '%(confdir)s/test_project/templates',
    'reload': True,
    'debug' : True,
    'errors' : {
        '404' : '/error/404',
        '__force_dict__' : True
    }
}

# Custom Configurations must be in Python dictionary format::
#
# foo = {'bar':'baz'}
# 
# All configurations are accessible at::
# pecan.conf

Nothing in the configuration file above is actually required for Pecan to run. If you fail to provide some values, Pecan will fill in the missing things it needs to run.

You can also add your own configuration as dictionaries.

For more specific documentation on configuration, see the Configuration section.

Root Controller

The Root Controller is the root of your application.

This is how it looks in the project template:

from pecan import expose, request
from formencode import Schema, validators as v
from webob.exc import status_map


class SampleForm(Schema):
    name = v.String(not_empty=True)
    age = v.Int(not_empty=True)


class RootController(object):
    @expose('index.html')
    def index(self, name='', age=''):
        return dict(errors=request.validation_errors, name=name, age=age)

    @expose('success.html', schema=SampleForm(), error_handler='index')
    def handle_form(self, name, age):
        return dict(name=name, age=age)

    @expose('error.html')
    def error(self, status):
        try:
            status = int(status)
        except ValueError:
            status = 0
        message = getattr(status_map.get(status), 'explanation', '')
        return dict(status=status, message=message)

You can specify additional classes if you need to do so, but for now we have an index and handle_form method.

index: is exposed via the decorator @expose (which in turn uses the index.html template) at the root of the application (http://127.0.0.1:8080/), so anything that hits the root of your application will touch this method.

Notice that the index method returns a dictionary - this dictionary is used as a namespace to render the specified template (index.html) into HTML.

Since we are performing form validation and want to pass any errors we might get to the template, we set errors to receive form validation errors that may exist in request.validation_errors.

handle_form: receives 2 arguments (name and age) that are validated through the SampleForm schema.

The error_handler has been set to index. This means that when errors are raised, they will be sent to the index controller and rendered through its template.

error: Finally, we have the error controller that allows your application to display custom pages for certain HTTP errors (404, etc...).

Application Interaction

If you still have your application running and you visit it in your browser, you should see a page with some information about Pecan and a form so you can play a bit.