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+.. _qtut_hello_world:
+
+================================
+01: Single-File Web Applications
+================================
+
+What's the simplest way to get started in Pyramid? A single-file module. No
+Python packages, no ``pip install -e .``, no other machinery.
+
+
+Background
+==========
+
+Microframeworks are all the rage these days. "Microframework" is a marketing
+term, not a technical one. They have a low mental overhead: they do so little,
+the only things you have to worry about are *your things*.
+
+Pyramid is special because it can act as a single-file module microframework.
+You can have a single Python file that can be executed directly by Python. But
+Pyramid also provides facilities to scale to the largest of applications.
+
+Python has a standard called :term:`WSGI` that defines how Python web
+applications plug into standard servers, getting passed incoming requests, and
+returning responses. Most modern Python web frameworks obey an "MVC"
+(model-view-controller) application pattern, where the data in the model has a
+view that mediates interaction with outside systems.
+
+In this step we'll see a brief glimpse of WSGI servers, WSGI applications,
+requests, responses, and views.
+
+
+Objectives
+==========
+
+- Get a running Pyramid web application, as simply as possible.
+
+- Use that as a well-understood base for adding each unit of complexity.
+
+- Initial exposure to WSGI apps, requests, views, and responses.
+
+
+Steps
+=====
+
+#. Make sure you have followed the steps in :doc:`requirements`.
+
+#. Starting from your workspace directory
+   (``~/projects/quick_tutorial``), create a directory for this step:
+
+   .. code-block:: bash
+
+    $ mkdir hello_world; cd hello_world
+
+#. Copy the following into ``hello_world/app.py``:
+
+   .. literalinclude:: hello_world/app.py
+    :linenos:
+
+#. Run the application:
+
+   .. code-block:: bash
+
+    $ $VENV/bin/python app.py
+
+#. Open http://localhost:6543/ in your browser.
+
+
+Analysis
+========
+
+New to Python web programming? If so, some lines in the module merit
+explanation:
+
+#. *Line 11*. The ``if __name__ == '__main__':`` is Python's way of saying,
+   "Start here when running from the command line", rather than when this
+   module is imported.
+
+#. *Lines 12-14*. Use Pyramid's :term:`configurator` to connect :term:`view`
+   code to a particular URL :term:`route`.
+
+#. *Lines 6-8*. Implement the view code that generates the :term:`response`.
+
+#. *Lines 15-17*. Publish a :term:`WSGI` app using an HTTP server.
+
+As shown in this example, the :term:`configurator` plays a central role in
+Pyramid development. Building an application from loosely-coupled parts via
+:ref:`configuration_narr` is a central idea in Pyramid, one that we will
+revisit regularly in this *Quick Tutorial*.
+
+
+Extra Credit
+============
+
+#. Why do we do this:
+
+   .. code-block:: python
+
+      print('Incoming request')
+
+   ...instead of:
+
+   .. code-block:: python
+
+      print 'Incoming request'
+
+#. What happens if you return a string of HTML? A sequence of integers?
+
+#. Put something invalid, such as ``print xyz``, in the view function. Kill
+   your ``python app.py`` with ``ctrl-C`` and restart, then reload your
+   browser. See the exception in the console?
+
+#. The ``GI`` in ``WSGI`` stands for "Gateway Interface". What web standard is
+   this modelled after?