MultiBottle

Multi-App Sites With Bottle

The Perfect Framework?

Bottlepy is a perfect framework for a simple website, but more debatable is the choice of bottlepy for more complex multi app sites.

The mainstream current wisdom is that for a more complex website, django is the perfect choice.

I would argue that this conventional wisdom has a flaw. The flaw is that as site complexity increases, so does the chance a complex predefined structure is not a perfect fit. Further, comparing the performance of bottle with django, bottle delivers the performance more critical for the complex environment.

Certainly, the chances of an 'off the shelf' solution being available in django is far more likely. If living with the 'off the shelf' as is will work, this is powerful arugment for django. But if a lot of change will be needed, the pendulum swings back to the cleaner approach of bottle.

OK, bottle is perfect for a simple site. What holds bottle back for a more complex app?

Multi App Sites

Lets consider a website comprised of smaller 'subapps'. First Question: What would utopia look like? Second Question: How close does bottle get to utopia?

Utopia ++++++

Key Points:

• The structure for multiple apps has zero impact on single app websites
• An app can be built as single app or a 'subapp' component of a multi app site without code changes
• Within a multi app system, each app can be self contained using its own folder structure
• Apps could be nested to any level
• The complete system is git (or other VCS) friendly

In practice this would imply something like the following folder structure::

App (folder)
  file1
  file2
  static (folder)
    static_file1
    static_file2
  views (folder)
    view_file1
    view_file2
  sub_app1 (folder)
    file1
    static (folder)
      static_file1
    views
      view_file1
etc

The possible contentious point is having statics and views in eash sub_app rather than in their own folder trees. The above is an 'app tree' approach, and I will call the alternative a views/static tree approach. I suggest that the logical structure above is utopia for git and development, but the multi app system should be flexible and support separate image/static trees, even if not an automatic default. Single file structure can support both trees through symlinks, but both structures should be workable with a multi app system both with and without the use of symlinks.

So Far With Bottle ++++++++++++++++++

The 'app' Structure

---

Applications in bottle are instances of the 'Bottle' class. Each instance of the bottle module has an AppStack, which is a list of Bottle instances, or a list of 'apps'.

Both 'app' and 'default_app' reference this AppStack. Import either 'app' or 'default_app' to access the AppStack instance. This can be somewhat confusing having 'app' as a list as much documentation and general ideas these days descibes an 'app' as an instance of Bottle. Each one is an app in most languages and I recommend importing 'app' as 'apps'.

The AppStack is actually a class based on list, but with two extra methods, 'call' and 'push'. So app[0] (or default_app[0]) would retrieve the fist app in the list, and so on. Using the call method 'app()' is identical to 'app[-1]' and retries the last app in the list. The 'push' method, appends a new Bottle instance to the list. ::

from bottle import app as apps, default_app # these are two references to the same 'AppStack' list of Bottle instances from bottle import Bottle # the class to instance 'apps'

app[0] # retrieve the first Bottle instance in the Appstack list app[-1] # retrive the last Bottle instance in the list app() # same as app[-1] myApp = Bottle() # instance a new Bottle application app.push(myApp) # add the new application to the AppStack list myApp2 = app.push(Bottle()) # create a Bottle instance and add to the app list myApp3 = app.push() # same as above. push() with no parameter instance and pushes a new Bottle instance

Default Bottle Instance

---

The bottle module not only instances an AppStack() with both the names 'app' and 'default_app', also one instance of a Bottle object (or app) is pre-added to the AppStack. Note using this 'pre-added' instance of Bottle() is dangerous, because serveral modules can accidentally use the same instance. For the AppStack, there is only on instance so no problem. app() or default_app() both retrieve the last app added to the AppStack, which will initially be the Bottle instance created internally to the bottle module. @route etc decorators will by default use the last Bottle instance added to the AppStack list. If using two apps in the same module, @route etc will by default work with the automatically created app until a new app is instanced e.g. ::

from bottle import Bottle, route, app as apps

@route('/page')  # works with default app
def pageapp1():
    pass

app1 = apps()  # save default app - you need to be sure only you will use this!
newapp = Bottle()  # use 'newapp = apps.push()' to do all steps at once

@route('/page1')  # route using last app in AppStack which is still app1
def page1():
    pass

@newapp.route('/page2')  # explict route for 'newapp'
def page2():
    pass

apps.push(newapp)  # add 'newapp' to AppStack, which will make newapp now the default

@route('/page2b')  # another route for newapp
@newapp.route('/page2c') # explict route for same app
def page2b():
    pass

app1.route('/anotherpage')  # explicit route for first app
def pageNot2b():
    pass

Combining Apps and Routes

---

So even in a single file, it is possible to work with multiple bottle instances or 'apps'. But only one app is actually 'run', so it is necessary to combine these apps to run collectively.

Bottle provides two ways of combining apps::

mainapp.mount('/subapp', subapp1)  # mount subapp with '/subapp' as a path prefix
mainapp.merge(subapp2)  # mount subapp2 at site root

If 'subapp1' has a @route('main') then with the 'mount' above it, this 'main' route would become '/subapp/main'. ::

mainapp.mount('/', subapp)
    and
mainapp.merge(subapp)

Would seem to be the same, however using 'mount' in this case is forbidden and 'merge' is required. I am unsure why as it would seem using 'mount' for both cases would be elegant. ::

#hello app
from bottle import route,app as apps

myapp= apps.push()

@route('/hello')
def hello():
    return 'the main hello app page'

Main file::

#main app  - helloapp is used as a sub app
from bottle import route,mount,run,app as apps
from helloapp import myapp as subapp

myapp=apps.push() #note if both files used apps(), they would share the same app

@route('/')
@route('/home')
def home():
    return 'site home page'

myapp.mount('/sub')
myapp.run()

This simple structure allows for a separate python program for each 'app'.

Note: using 'apps.push()' in place of 'apps()' every time means that there is one unused Bottle instance on the AppStack. But that is better than accidentally using that one automatic Bottle() twice.

What about folders? +++++++++++++++++++ The previous section covers all that is needed for multiple applications where all files share the same folders. Which effectively means the 'apps' are developed together. Python files in the same folder, all statics in the same statics folder and all views in the same views folder. However the 'Utopia' was to allow the subapp to live in its own folder with self contained static and views folders. Simply adding an init.py to the sub app and adjusting the import allows the sub app to live in its own folder and a .gitignore line can even keep the projects separate if you use Git. The import simply becomes::

from sub/helloapp import myapp as subapp

But what about views and statics?

---

By default bottle creates two template directories::

['./', './views/']

In reality this is only useful if bottle is started with the current directory set to the app. On some servers, this does not happen so these settings are of no use. If the app is accessed from 'pythonpath' for example, the the current directory could be anywhere.

So sometimes the default settins work, in other cases they do not. Whether the settings work is largely deployment specific.

Further, in the above 'hello' app example, even if the default settings work, we would want the hello app, which is in the 'sub' folder ro have the following paths::

[ './sub/', './sub/views/' './', './views/' ]

Alternatively, with the alternate scheme mentioned in the 'utopia' secion the following could be desired::

[ './sub/', './views/sub/' './', './views/' ]

We could modify the code for each deployment, but this is not desirable. Goals

---

The goals are:

• minimise changes between deployments
• support git based developments

Solution.

---

A single file 'siteSettings.py' (or siteSettings.json or .conf), to override defaults meets all solution criteria. Bottle already supports app configuration files, but these serve a different purpose. Firstly these hold settings for each app as opposed to the 'site' which has an impact on all apps. Secondly, they are intended to store all app settings, rather than only the site settings. Specifically this means excluding the app config file through .gitignore is not desireable, whereas the site config file is specifically designed to be excluded through .gitignore.

A very common use of the site config is that testing of a site will occur with one site config on a local developer machine, then move to another site config on a test host, before becomming live on a third live host site configuration.

(The actual storage format and file name will depend on feedback as to what is popular)

A 'site' object holdings all 'deployment' based settings is added to each 'app'.

This object provides simple access to deployment specific data, and the object is built using defaults, overridden by default overrides from the 'Site' class in the siteSettings.py file.

The default values produce the following 'site' objects, in a 'main' app or a 'sub' app added through 'merge' respectively.

+-----------+--------------------------+------------------------+------------------------+ | field + siteSettings value + value in default 'app' + value in 'sub' app + | + (default) + + + +===========+==========================+========================+========================+

• views + .{path}/views/, .{path} + [ ./views , ./ ] + [ ./sub/views, ./subs/ +

•       +                          +                        +   , ./views , ./  ]    +
  

+-----------+--------------------------+------------------------+------------------------+

• static + .{path}/static/, + ./static/ + [ ./static/ +

•       +                          +                        +   ,  ./sub/static/  ]  +
  

+-----------+--------------------------+------------------------+------------------------+

• appStatic + .{path}/static/ + ./static/ + [ ./sub/static/ ] + +-----------+--------------------------+------------------------+------------------------+
• appURL + {path}/ + / + /subURL + +-----------+--------------------------+------------------------+------------------------+

Note::

The '/subURL' in the URL is derived from the path in the 'merge' app1.merge('/subURL',subapp) The './sub' in the static and views paths is derived from the python 'import' from sub import subapp

The name of the module (or folder) used for the subapp need not match the URL prefix
used with merge and for accessing the subapp. In this example 'subURL' as a prefix
within web links,  but accessing the 'sub' folder within the application folder tree.

The folder or module {path} is constructed from the python module path, and then used with .format() to build values in instances of 'site'. The 'appURL' attribute is passed to templates, so pages can use the 'appURL' value to link to other pages or resources (including statics) referenced by the page.

So the results above assume the 'sub' app is imported as follows::

from sub import subapp

To override these defaults, create a 'siteSettings' module in the main project folder and add a 'Site' class with values to over-ride the defaults::

class Site:
   views = './views{path}/'  #all views in tree within views folder

# example of deployment where current folder is not set
class Site:
    views = '/home/theApp{path}/views/', '/home/theApp{path}/'
    #project in 'theApp' folder

Values are only required where the default is to be changed.

Note this system is currently implemented through 'newMerge' and method 'app.static_file' bottle could be upgraded with full backward compatibility

Name Conflicts.

---

So why would the same name appear in both the main project and the sub 'app'?

There are two possible reasons:

• the app holds a standin for what is hoped would be 'site global'
• the app holds a value designed to override a 'site global'

In the first case, it is desired to look first in the 'global' location, and the opposite for the second case. Currently the code implements the 'global first' approach on the thought that if the app wants a unique value it can choose a unique name