3: Configuration Files and pserve

Pyramid has a first-class concept of configuration distinct from code. This approach is optional, but its presence makes it distinct from other Python web frameworks.

Objectives

• Create an application driven by a .ini file
• Startup the application with Pyramid’s pserve command
• Move code into the package’s __init__.py

Steps

1. Let’s begin using the previous package as a starting point for a new distribution, then making it active:

   (env33)$ cd ..; cp -r step02 step03; cd step03
   (env33)$ python3.3 setup.py develop
   

2. Pyramid can use a .ini-formatted configuration file as its launching point. Type the following into development.ini inside step03:

   [app:main]
   use = egg:tutorial
   pyramid.reload_templates = true
   
   [server:main]
   use = egg:pyramid#wsgiref
   host = 0.0.0.0
   port = 6547
   
   [loggers]
   keys = root
   
   [handlers]
   keys = console
   
   [formatters]
   keys = generic
   
   [logger_root]
   level = INFO
   handlers = console
   
   [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
   

3. Many Pyramid apps put the logic for setting up the WSGI app into the distribution’s __init__.py, so enter the following into tutorial/__init__.py:

   from pyramid.config import Configurator
   
   
   def main(global_config, **settings):
       config = Configurator(settings=settings)
       config.add_route('hello', '/')
       config.scan()
       return config.make_wsgi_app()
   

4. Let’s eliminate our wikiapp.py, as its functionality is now merged into __init__.py:

   (env33)$ rm tutorial/wikiapp.py*
   

   We do .py* to ensure we get the byte-compiled .pyc file.

5. Run the WSGI application with:

   (env33)$ pserve development.ini
   

6. Open http://127.0.0.1:6547/ in your browser.

Analysis

Our development.ini file is read by pserve and serves to bootstrap our application. Processing then proceeds as described in the Pyramid chapter on application startup:

• pserve looks for [app:main] and finds use = egg:tutorial
• The package’s setup.py has defined this (lines 9-10) for the distribution (egg) as tutorial:main
• The tutorial distribution’s __init__ has a main function
• This function is invoked, with the values from certain .ini sections passed in

The .ini file is also used for two other functions:

• [server:main] wires up the choice of WSGI server for your WSGI application
• Pyramid uses Python standard logging, which needs a number of configuration values. The .ini serves this function.

In this case, pserve finds the server defined by [server:main] and the application defined by [app:main]. The latter’s use = egg:tutorial governs

The code from wikiapp.py that launched our application not only was moved to __init__.py...it also got shorter, as it didn’t need to wire up a WSGI server.

Extra Credit

1. Is it possible to develop your application separately from the configuration? Is that a good idea?
2. Can you have more than one .ini file for an application?
3. If you don’t like configuration and/or .ini files, could you do this yourself in Python code?