Tutorial basic PT.1

#Flask-XXL

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###Contents:

1. OverView
2. Getting Started
3. The Settings
   • INSTALLED_BLUEPRINTS
   • TEMPLATE_FILTERS
   • CONTEXT_PROCESSORS
   • ROUTE_MODULES
   • TEMPLATE_LOADERS
   • EXTRA_TEMPLATE_DIRS_
4. Flask, python and MTV
5. Views - part1 begining
6. Templates - part1 begining
7. Models
8. Templates - Advanced
9. Widgets
10. Extending
11. Etc.....

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##Ch.1 - Overview

====================

Flasks creator had the idea, that Django was somewhat of an elephant,(they do say so themselves). And Who needs an elephant? Well I say there are plenty of cases to use an elephant, but why does it have to be Django? I purpose to use flask for the same monumental tasks for which we would normally look to somthing bigger. Flask by design is a small framework, it is very good at being a light, agile framework to build upon. That is why i have created Flask-XXL. Using the Flask Factory pattern, specifically one borrowed from "Flask-Kit", that uses a few settings, very similar to Django, to automatically do some things for the user, i used to find this annoying in Django, it constantly doing things behind my back. Now, i find the freedom inspiring, there is so much boilerplate i can now forget about, now i understand what everyone likes about Django. But flask is so lightweight and transparent, the source easy to read. But im rambling, so let me show you what i mean in the first example.

##Ch.2 - Getting Started

============================

a typical small flask app might start like this

from flask import Flask,url_for,redirect,session,g,flash

app = Flask(__name__)

@app.route('/')
def index():
    return "hello World"

if __name__ == "__main__":
    app.run()

but this is obviously a very small example. If you really want a system that can expand you should start using Blueprints

from flask import Blueprint

blog = Blueprint('blog',__name__,
       template_folder='templates',
       url_prefix='/blog')
from .views import *

now most tutorials say to keep going like the original example

@blog.route('/')
def blog():
    return "my blog"

but this is where we take our turn,

so the first thing to look at in any big web system like this, id say is the settings file, or whichever config holds the database info.

here thats settings.py a file that is very similar now to djangos settings.py

##Ch.3 Settings file

======================

the main settings here are

                            #Django Equivilants
                            #++++++++++++++++++++
INSTALLED_BLUEPRINTS = [    #<-- INSTALLED_APPS
        XXXXX
]
TEMPLATE_FILTERS = [   [    #<-- Django dosent have a setting for this feature,  just a clunky api
        XXXXXX
]
CONTEXT_PROCESSORS = [      #<-- TEMPLATE_CONTEXT_PROCESSORS
        XXXXXXX
]
ROUTE_MODULES = [           #<-- ROOT_URLCONF
        XXXXXX
]
TEMPLATE_LOADERS = [        #<-- TEMPLATE_LOADERS
        xxxxxx
]
EXTRA_TEMPLATE_DIRS = [     #<-- TEMPLATE_DIRS
        xxxxxxxx
]

These 4 settings handle many things that normally take quite some time to get right, and boils them down to a few easy processes.

###INSTALLED_BLUEPRINTS

+++++++++++++++++++++++

this takes the place of Djangos INSTALLED_APPS but for flask blueprints. It works the same way. just add the import path of a Blueprint, it can be anywhere, even in a seperate installed package, as long as its importable on your PYTHONPATH. Heres a an example of the setting

INSTALLED_BLUEPRINTS = [
            'flask.ext.xxl.apps.auth.auth', #these are a few of the blueprints 
            'flask.ext.xxl.apps.page.page', #built into flask-xxl
            'admin.admin', # these are blueprints inside the webapp
            'blog.blog'
 ]

###TEMPLATE_FILTERS

+++++++++++++++++++

now in Django you can write and register your own template filters, but i think its kind of a hassle. Flask has an easy way to do it that ive always loved, but this makes it much eaiser.

1. step1 - write the filter heres an example that will pull all of the x's from the input and return the result

    def filter_out_xs(data):
        rtn = ''
        for char in data:
            if char.lower() == 'x':
                pass
            else:
                rtn += char
        return rtn
   

2. step2 just add to the setting, if it was in myapp.template_filters i would put

    TEMPLATE_FILTERS = [
        'myapp.template_filters.filter_out_xs',
    ]
   

then it could be used in a template like this:

        {{ someval|filter_out_xs }}

and of the input was

'xx55x76'

the output would be

'5576'

###CONTEXT_PROCESSORS

+++++++++++++++++++++

A better way to think of context_processors, is global template variables. Basicly they are functions you can define, that can return data and objects into the global template environment. Then those objects or that data, is avialiable upon rendering templates. This can be very powerful, and it is just as easy here as it is in Django.

Heres a simple example:

def simple_context():
    return dict(somevar='someval')
    
def extra_func():
    return 'somthing i computed'
    
def complicated_context():
    return dict(complicated=extra_func)

now this is in myapp/context_processors.py in the settings file id put

CONTEXT_PROCESSORS = [
    'myapp.context_processors.simple_context',
    'myapp.context_processors.complicated_context',
]

then in my templates somevar and extra_func would be avialible

##Ch. 4 Flask, Python.. and MTV

---

Now most people, well at least most programmers, know about the MVC or Model, View, Controller pattern. In Python things tend to work a little differently, first lets look at the traditional MVC pattern.

• a model class mapping database tables to objects and associcated data within the program
  • M
• a few view classes (with related latout,block or template files/classes) to process that data for display
  • V
• finally You would normally have a some kind of front controller class that routes http requests to the views
  • C

now python dosent handle the http requests as cleanly as some languages might, and as a consiquense of that the routing mainly happens behind the scenes, and is handeled on by the user via either a config style syntax, or a decoraotor syntax ie:

config style:

routes = (
  ((Bp),
  ('/',AView.as_view('view')),
 )

decorator style:

@app.route('/')
def view_func():
    return a_view()

and this leads us to our next setting

###ROUTE_MODULES

++++++++++++++++

now flask and its many tutorials teach the decorator style from above, arguing that it makes debugging a crashed site eaiser because the function that crashed the site is defined right next to the url that called it. Which makes sense, until your project grows to 500+ lines, then those functions start getting harder to sift through. Not to mention that the decorator syntax makes it easy to assign different request methods to the same functions, then checking in the function which type of request was sent and basing the response on that. This to me seems like a lot for nothing. The great thing about it though is it uses simple string matching to line up incoming requests with the defined url rules, this isnt as powerful as some systems, but it is simple to understand and you can get up and running in a short matter of time.

Django on the other hand uses the config style, not exactly like my example above, but close enough. In the Django world each app you add to your project you give a urls.py file that imports your view functions/classes and matchs them to url rules. I find this makes debugging actually eaiser. Anytime your site crashes, the url will tell you which urls.py file to look in, then just find that line and theres your offending function. The main downside with Django is the it uses a complex system of "regular expressions" to parse and match the incoming url requests to the defined url rules. I must admit that no matter how trivial they may sound, regular expressions are anything but.

So for my system i took the best of both of those worlds.

• a urls.py file

  • each app (blueprint in flask speak) gets its own urls.py for routing
    

• string comparisons for matching requests to url rules

Here is a "small" example to show you how a view and its routing are defined: (dont mind the flask-xxl imports, ill explain them later)

views.py

from flask.ext.xxl.core.baseviews import BaseView

class ExampleView(BaseView):
   _template = 'example.html'
   
   def get(self):
       return self.render()

now we need a blueprint to plug it into

example.py

from flask import Blueprint

example = Blueprint('example',__file__)
from .views import *

then we need to define our route

urls.py

from .views import ExampleView
from example import eaxmple

routes = [
   ((example),
   ('/',ExampleView.as_view('example')),
)]

then just define the url module in the ROUTE_MODULE setting

settings.py

ROUTE_MODULES = (
   'myapp.example.urls',
)

now i know this may seem like a bit much for such a small example app, but lets not forget that this is called Flask-XXL, so its really not intended for such small requirments, if you plan on having a small web-app, with few blueprints, that is what Flask is made for, but when you plan on your application growing and you want to handle it with clean system, that is what flask-xxl is for.

##Ch. 5. Views - part1 begining

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from here on out we will dump our example app and start fresh, building what hopefully will grow to be a full-featured project management suite. But we will start from the start, or at least as far back as you need to when using flask-xxl.

Now one thing i think almost everyone can agree Django did well was project / (module/app) setup.

with a simple

$ manage.py startproject

or

$ manage.py startapp

you are asked a few simple questions about your intentions and wham boom, youve got a new project/app, or at least a number of the files youll want to start off with, as well as a few helpful imports / commented notes to help speed up development.

Thats the way things should work, so here to start we use

$ flaskxxl.py startproject

##To Be Continued .....

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