Working on 0.6 documentation.

docs/tutorial/3-files.rst

@@ -3,6 +3,49 @@ Part 3: Working with Files
 
 .. include:: _wip_note.rst
 
+Writing to the console is nice, but using files is probably more realistic.
+
+Let's see how to use a few builtin writers and both local and remote filesystems.
+
+
+Filesystems
+:::::::::::
+
+In |bonobo|, files are accessed within a **filesystem** service which must be something with the same interface as
+`fs' FileSystem objects <https://docs.pyfilesystem.org/en/latest/builtin.html>`_. As a default, you'll get an instance
+of a local filesystem mapped to the current working directory as the `fs` service. You'll learn more about services in
+the next step, but for now, let's just use it.
+
+
+Writing using the service
+:::::::::::::::::::::::::
+
+Although |bonobo| contains helpers to write to common file formats, let's start by writing it manually.
+
+.. code-block:: python
+
+    from bonobo.config import use
+    from bonobo.constants import NOT_MODIFIED
+
+    @use('fs')
+    def write_repr_to_file(*row, fs):
+        with fs.open('output.txt', 'a+') as f:
+            print(row, file=f)
+        return NOT_MODIFIED
+
+Then, update the `get_graph(...)` function, by adding `write_repr_to_file` just before your `PrettyPrinter()` node.
+
+Let's try to run that and think about what happens.
+
+Each time a row comes to this node, the output file is open in "append or create" mode, a line is written, and the file
+is closed.
+
+This is **NOT** how you want to do things. Let's rewrite it so our `open(...)` call becomes execution-wide.
+
+
+
+
+
 * Filesystems
 
 * Reading files
@@ -21,4 +64,4 @@ You now know:
 
 * How to ...
 
-**Next: :doc:`4-services`**
+It's now time to jump to :doc:`4-services`.