.. _commands: Command Line Pecan ================== Any Pecan application can be controlled and inspected from the command line using the built-in :command:`pecan` command. The usage examples of :command:`pecan` in this document are intended to be invoked from your project's root directory. Serving a Pecan App For Development ----------------------------------- Pecan comes bundled with a lightweight WSGI development server based on Python's :py:mod:`wsgiref.simple_server` module. Serving your Pecan app is as simple as invoking the ``pecan serve`` command:: $ pecan serve config.py Starting server in PID 000. serving on, view at and then visiting it in your browser. The server ``host`` and ``port`` in your configuration file can be changed as described in :ref:`server_configuration`. .. include:: reload.rst :start-after: #reload The Interactive Shell --------------------- Pecan applications also come with an interactive Python shell which can be used to execute expressions in an environment very similar to the one your application runs in. To invoke an interactive shell, use the ``pecan shell`` command:: $ pecan shell config.py Pecan Interactive Shell Python 2.7.1 (r271:86832, Jul 31 2011, 19:30:53) [GCC 4.2.1 (Based on Apple Inc. build 5658) The following objects are available: wsgiapp - This project's WSGI App instance conf - The current configuration app - webtest.TestApp wrapped around wsgiapp >>> conf Config({ 'app': Config({ 'root': 'myapp.controllers.root.RootController', 'modules': ['myapp'], 'static_root': '/Users/somebody/myapp/public', 'template_path': '/Users/somebody/myapp/project/templates', 'errors': {'404': '/error/404'}, 'debug': True }), 'server': Config({ 'host': '', 'port': '8080' }) }) >>> app >>> app.get('/') <200 OK text/html body='\n ...\n\n'/936> Press ``Ctrl-D`` to exit the interactive shell (or ``Ctrl-Z`` on Windows). Using an Alternative Shell ++++++++++++++++++++++++++ ``pecan shell`` has optional support for the `IPython `_ and `bpython `_ alternative shells, each of which can be specified with the ``--shell`` flag (or its abbreviated alias, ``-s``), e.g., :: $ pecan shell --shell=ipython config.py $ pecan shell -s bpython config.py .. _env_config: Configuration from an environment variable ------------------------------------------ In all the examples shown, you will see that the :command:`pecan` commands accepted a file path to the configuration file. An alternative to this is to specify the configuration file in an environment variable (:envvar:`PECAN_CONFIG`). This is completely optional; if a file path is passed in explicitly, Pecan will honor that before looking for an environment variable. For example, to serve a Pecan application, a variable could be exported and subsequently be re-used when no path is passed in. :: $ export PECAN_CONFIG=/path/to/app/config.py $ pecan serve Starting server in PID 000. serving on, view at Note that the path needs to reference a valid pecan configuration file, otherwise the command will error out with a message indicating that the path is invalid (for example, if a directory is passed in). If :envvar:`PECAN_CONFIG` is not set and no configuration is passed in, the command will error out because it will not be able to locate a configuration file. Extending ``pecan`` with Custom Commands ---------------------------------------- While the commands packaged with Pecan are useful, the real utility of its command line toolset lies in its extensibility. It's convenient to be able to write a Python script that can work "in a Pecan environment" with access to things like your application's parsed configuration file or a simulated instance of your application itself (like the one provided in the ``pecan shell`` command). Writing a Custom Pecan Command ++++++++++++++++++++++++++++++ As an example, let's create a command that can be used to issue a simulated HTTP GET to your application and print the result. Its invocation from the command line might look something like this:: $ pecan wget config.py /path/to/some/resource Let's say you have a distribution with a package in it named ``myapp``, and that within this package is a ``wget.py`` module:: # myapp/myapp/wget.py import pecan from webtest import TestApp class GetCommand(pecan.commands.BaseCommand): ''' Issues a (simulated) HTTP GET and returns the request body. ''' arguments = pecan.commands.BaseCommand.arguments + ({ 'name': 'path', 'help': 'the URI path of the resource to request' },) def run(self, args): super(GetCommand, self).run(args) app = TestApp(self.load_app()) print app.get(args.path).body Let's analyze this piece-by-piece. Overriding the ``run`` Method ,,,,,,,,,,,,,,,,,,,,,,,,,,,,, First, we're subclassing :class:`~pecan.commands.base.BaseCommand` and extending the :func:`~pecan.commands.base.BaseCommandParent.run` method to: * Load a Pecan application - :func:`~pecan.core.load_app` * Wrap it in a fake WGSI environment - :class:`~webtest.app.TestApp` * Issue an HTTP GET request against it - :meth:`~webtest.app.TestApp.get` Defining Custom Arguments ,,,,,,,,,,,,,,,,,,,,,,,,, The :attr:`arguments` class attribute is used to define command line arguments specific to your custom command. You'll notice in this example that we're *adding* to the arguments list provided by :class:`~pecan.commands.base.BaseCommand` (which already provides an argument for the ``config_file``), rather than overriding it entirely. The format of the :attr:`arguments` class attribute is a :class:`tuple` of dictionaries, with each dictionary representing an argument definition in the same format accepted by Python's :py:mod:`argparse` module (more specifically, :meth:`~argparse.ArgumentParser.add_argument`). By providing a list of arguments in this format, the :command:`pecan` command can include your custom commands in the help and usage output it provides. :: $ pecan -h usage: pecan [-h] command ... positional arguments: command wget Issues a (simulated) HTTP GET and returns the request body serve Open an interactive shell with the Pecan app loaded ... $ pecan wget -h usage: pecan wget [-h] config_file path $ pecan wget config.py /path/to/some/resource Additionally, you'll notice that the first line of the docstring from :class:`GetCommand` -- ``Issues a (simulated) HTTP GET and returns the request body`` -- is automatically used to describe the :command:`wget` command in the output for ``$ pecan -h``. Following this convention allows you to easily integrate a summary for your command into the Pecan command line tool. Registering a Custom Command ++++++++++++++++++++++++++++ Now that you've written your custom command, you’ll need to tell your distribution’s ``setup.py`` about its existence and reinstall. Within your distribution’s ``setup.py`` file, you'll find a call to :func:`~setuptools.setup`. :: # myapp/setup.py ... setup( name='myapp', version='0.1', author='Joe Somebody', ... ) Assuming it doesn't exist already, we'll add the ``entry_points`` argument to the :func:`~setuptools.setup` call, and define a ``[pecan.command]`` definition for your custom command:: # myapp/setup.py ... setup( name='myapp', version='0.1', author='Joe Somebody', ... entry_points=""" [pecan.command] wget = myapp.wget:GetCommand """ ) Once you've done this, reinstall your project in development to register the new entry point. :: $ python setup.py develop Then give it a try. :: $ pecan wget config.py /path/to/some/resource