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Startup

When you cause a Pyramid application to start up in a console window, you’ll see something much like this show up on the console:

$ pserve myproject/MyProject.ini
Starting server in PID 16601.
serving on 0.0.0.0:6543 view at http://127.0.0.1:6543

This chapter explains what happens between the time you press the “Return” key on your keyboard after typing pserve myproject/MyProject.ini and the time the line serving on 0.0.0.0:6543 ... is output to your console.

The Startup Process

The easiest and best-documented way to start and serve a Pyramid application is to use the pserve command against a PasteDeploy .ini file. This uses the .ini file to infer settings and starts a server listening on a port. For the purposes of this discussion, we’ll assume that you are using this command to run your Pyramid application.

Here’s a high-level time-ordered overview of what happens when you press return after running pserve development.ini.

  1. The pserve command is invoked under your shell with the argument development.ini. As a result, Pyramid recognizes that it is meant to begin to run and serve an application using the information contained within the development.ini file.

  2. The framework finds a section named either [app:main], [pipeline:main], or [composite:main] in the .ini file. This section represents the configuration of a WSGI application that will be served. If you’re using a simple application (e.g. [app:main]), the application’s paste.app_factory entry point will be named on the use= line within the section’s configuration. If, instead of a simple application, you’re using a WSGI pipeline (e.g. a [pipeline:main] section), the application named on the “last” element will refer to your Pyramid application. If instead of a simple application or a pipeline, you’re using a “composite” (e.g. [composite:main]), refer to the documentation for that particular composite to understand how to make it refer to your Pyramid application. In most cases, a Pyramid application built from a scaffold will have a single [app:main] section in it, and this will be the application served.

  3. The framework finds all logging related configuration in the .ini file and uses it to configure the Python standard library logging system for this application. See Logging Configuration for more information.

  4. The application’s constructor named by the entry point reference on the use= line of the section representing your Pyramid application is passed the key/value parameters mentioned within the section in which it’s defined. The constructor is meant to return a router instance, which is a WSGI application.

    For Pyramid applications, the constructor will be a function named main in the __init__.py file within the package in which your application lives. If this function succeeds, it will return a Pyramid router instance. Here’s the contents of an example __init__.py module:

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    from pyramid.config import Configurator
    
    
    def main(global_config, **settings):
        """ This function returns a Pyramid WSGI application.
        """
        config = Configurator(settings=settings)
        config.add_static_view('static', 'static', cache_max_age=3600)
        config.add_route('home', '/')
        config.scan()
        return config.make_wsgi_app()
    

    Note that the constructor function accepts a global_config argument, which is a dictionary of key/value pairs mentioned in the [DEFAULT] section of an .ini file (if [DEFAULT] is present). It also accepts a **settings argument, which collects another set of arbitrary key/value pairs. The arbitrary key/value pairs received by this function in **settings will be composed of all the key/value pairs that are present in the [app:main] section (except for the use= setting) when this function is called by when you run pserve.

    Our generated development.ini file looks like so:

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    [app:main]
    use = egg:MyProject
    
    pyramid.reload_templates = true
    pyramid.debug_authorization = false
    pyramid.debug_notfound = false
    pyramid.debug_routematch = false
    pyramid.default_locale_name = en
    pyramid.includes =
        pyramid_debugtoolbar
    
    [server:main]
    use = egg:waitress#main
    host = 0.0.0.0
    port = 6543
    
    # Begin logging configuration
    
    [loggers]
    keys = root, myproject
    
    [handlers]
    keys = console
    
    [formatters]
    keys = generic
    
    [logger_root]
    level = INFO
    handlers = console
    
    [logger_myproject]
    level = DEBUG
    handlers =
    qualname = myproject
    
    [handler_console]
    class = StreamHandler
    args = (sys.stderr,)
    level = NOTSET
    formatter = generic
    
    [formatter_generic]
    format = %(asctime)s %(levelname)-5.5s [%(name)s][%(threadName)s] %(message)s
    
    # End logging configuration
    

    In this case, the myproject.__init__:main function referred to by the entry point URI egg:MyProject (see development.ini for more information about entry point URIs, and how they relate to callables), will receive the key/value pairs {'pyramid.reload_templates':'true', 'pyramid.debug_authorization':'false', 'pyramid.debug_notfound':'false', 'pyramid.debug_routematch':'false', 'pyramid.debug_templates':'true', 'pyramid.default_locale_name':'en'}. See Environment Variables and .ini File Settings for the meanings of these keys.

  5. The main function first constructs a Configurator instance, passing the settings dictionary captured via the **settings kwarg as its settings argument.

    The settings dictionary contains all the options in the [app:main] section of our .ini file except the use option (which is internal to PasteDeploy) such as pyramid.reload_templates, pyramid.debug_authorization, etc.

  6. The main function then calls various methods on the instance of the class Configurator created in the previous step. The intent of calling these methods is to populate an application registry, which represents the Pyramid configuration related to the application.

  7. The make_wsgi_app() method is called. The result is a router instance. The router is associated with the application registry implied by the configurator previously populated by other methods run against the Configurator. The router is a WSGI application.

  8. A ApplicationCreated event is emitted (see Using Events for more information about events).

  9. Assuming there were no errors, the main function in myproject returns the router instance created by pyramid.config.Configurator.make_wsgi_app() back to pserve. As far as pserve is concerned, it is “just another WSGI application”.

  10. pserve starts the WSGI server defined within the [server:main] section. In our case, this is the Waitress server (use = egg:waitress#main), and it will listen on all interfaces (host = 0.0.0.0), on port number 6543 (port = 6543). The server code itself is what prints serving on 0.0.0.0:6543 view at http://127.0.0.1:6543. The server serves the application, and the application is running, waiting to receive requests.

Deployment Settings

Note that an augmented version of the values passed as **settings to the Configurator constructor will be available in Pyramid view callable code as request.registry.settings. You can create objects you wish to access later from view code, and put them into the dictionary you pass to the configurator as settings. They will then be present in the request.registry.settings dictionary at application runtime.

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