Handling requests

weppy provides several instruments to help you dealing with requests in your application. Let's see them.

The request object

When a request comes from a client, weppy binds useful informations about it on the request object, which can be accessed just with an import:

from weppy import request

It contains useful information about the current processing request, in particular:

attribute description
scheme could be http or https
method the request HTTP method
now a python datetime object created with request
client the ip of the client doing the request (if available)
cookies the cookies passed with the request
env contains environment variables like HTTP headers and WSGI parameters
isajax boolean which states if the request was made in ajax (check for xmlhttprequest presence in headers)

Please keep in mind that the now attribute uses UTC timezone by default. You can instead using the machine timezone:

app.now_reference = "local"

And if you need to access both the local time of the request and the utc one you can directly access these values on request using:

# request datetime in UTC timezone
# request datetime in local machine timezione

Now, let's see how to deal with request variables.

Request variables

weppy's request object also provides three important attributes about the active request, in particular:

attribute description
get_vars contains the url query variables
post_vars contains parameters passed into the request body
vars contains both the query variables and the body parameters

All these three attributes work in the same way, and the better way to understand it is with an example:

from weppy import App, request

app = App(__name__)

def post(id):
    editor = request.vars.editor
    if editor == "markdown":
        # code
    elif editor == "html":
        # code

Now, when a client call the url /post/123?editor=markdown, the editor parameter will be mapped into request.vars and we can access its value simply calling the parameter name as an attribute.

When the url doesn't contain the query parameter you're trying to look at, this will be None, so it's completely safe to call it, it wont raise an exception.

Now, what happens when the client does a POST request with this body

    "text": "this is an example post",
    "date": "2014-10-15"

on the url /post/123?editor=markdown ? Simple: the three request attributes we have seen will look like this:

>>> request.vars
<Storage {'date': '2014-10-15', 'text': 'this is a sample post', 'editor': 'markdown'}>
>>> request.get_vars
<Storage {'editor': 'markdown'}>
>>> request.post_vars
<Storage {'date': '2014-10-15', 'text': 'this is a sample post'}>

so you can always access the variables you need.

Handlers and Helpers

Quite often your application needs to perform operations before and after the request is actually processed by weppy using your exposed function.
weppy helps you doing this with the Hanlders:

from weppy import Handler

class MyHandler(Handler):
    def on_start(self):
        # code
    def on_success(self):
        # code
    def on_failure(self):
        # code

As you can see Handler provide methods to run your code before the request is processed by your function (with the on_start method) and after your function were executed, providing different methods depending on what happened on your function: if an exception is occurred weppy will call the on_failure method, otherwise the on_success method.

To register your handler to a function you just need to write:

@app.expose("/url", handlers=[MyHandler()])
def f():

And if you need to register your handler to all your application functions, you can omit the handler from the expose() decorator writing instead:

app.expose.common_handlers = [MyHandler()]

A peculiar Handler: the Helper class

Another common scenario you may encounter building your application is when you need to add same contents to your exposed functions' outputs, to make them available for the templates.

For example, let's say you have a function that makes your datetimes objects prettier:

>>> prettydate(datetime.now()-timedelta(days=1))
'One day ago'

And you would use it in your templates:

{{for post in posts:}}
<div class="post">
    <div class="post-date">{{=prettydate(post.date)}}</div>
    <div class="post-content">{{=post.text}}</div>

So, instead of adding prettydate to every exposed function, you can do this:

from weppy import Helper

class MyHelper(Helper):
    def prettydate(d):
        # your prettydate code

app.expose.common_helpers = [MyHelper()]

and you can access your prettydate function in every template.

So basically, the Helper class of weppy adds everything you define inside it (functions and attributes) into your exposed function returning dict.

Errors and redirects

Now, talking about handling requests, you would like to perform actions on errors.

If we look again at the given example for the request.vars, what happens when the user call the url without passing the editor query parameter? Maybe you want to redirect the client on a default parameter:

from weppy import redirect, url

def post(id):
    editor = request.vars.editor
    if editor == "markdown":
        # code
    elif editor == "html":
        # code
        redirect(url('post', id, vars={'editor': 'markdown'}))

which means that when the editor var is missing we force the user to the markdown one.

The redirect function of weppy accepts a string for the url, and acts like an exception, interrupting the execution of your code.

Maybe, you prefer to show your 404 page:

from weppy import abort

def not_found():

def post(id):
    editor = request.vars.editor
    if editor == "markdown":
        # code
    elif editor == "html":
        # code

and that's it.

So you've just learned three handy things of weppy:

  • redirect and abort allows you to stop the execution of your code;
  • you can set specific actions for your application when it encounters a particular HTTP error code with app.on_error();
  • you can use app.render_template() to render a specific template without the presence of an exposed function or a specific context.