Add documentation around ignoring errors

docs/source/user/configuration.rst

@@ -1,3 +1,5 @@
+.. _configuration:
+
 ====================
  Configuring Flake8
 ====================

docs/source/user/ignoring-errors.rst

@@ -0,0 +1,94 @@
+=============================
+ Ignoring Errors with Flake8
+=============================
+
+By default, |Flake8| has a list of error codes that it ignores. The list used
+by a version of |Flake8| may be different than the list used by a different
+version. To determine the default list, using :option:`flake8 --help` will
+show the output with the current default list.
+
+
+Changing the Ignore List
+========================
+
+If we want to change the list of ignored codes for a single run, we can use
+:option:`flake8 --ignore` to specify a comma-separated list of codes for a
+specific run on the command-line, e.g.,
+
+.. prompt:: bash
+
+    flake8 --ignore=E1,E23,W503 path/to/files/ path/to/more/files/
+
+This tells |Flake8| to ignore any error codes starting with ``E1``, ``E23``,
+or ``W503`` while it is running.
+
+.. note::
+
+    The documentation for :option:`flake8 --ignore` shows examples for how
+    to change the ignore list in the configuration file. See also
+    :ref:`configuration` as well for details about how to use configuration
+    files.
+
+
+In-line Ignoring Errors
+=======================
+
+In some cases, we might not want to ignore an error code (or class of error
+codes) for the entirety of our project. Instead, we might want to ignore the
+specific error code on a specific line. Let's take for example a line like
+
+.. code-block:: python
+
+    example = lambda: 'example'
+
+Sometimes we genuinely need something this simple. We could instead define
+a function like we normally would but in some contexts that distracts from
+what is actually happening. In those cases, we can also do:
+
+.. code-block:: python
+
+    example = lambda: 'example'  # noqa: E731
+
+This will only ignore the error from pycodestyle that checks for lambda
+assignments and generates an ``E731``. If there are other errors on the line
+then those will be reported.
+
+.. note::
+
+    If we ever want to disable Flake8 respecting ``# noqa`` comments, we can
+    can refer to :option:`flake8 --disable-noqa`.
+
+If we instead had more than one error that we wished to ignore, we could
+list all of the errors with commas separating them:
+
+.. code-block:: python
+
+    # noqa: E731,E123
+
+Finally, if we have a particularly bad line of code, we can ignore every error
+using simply ``# noqa`` with nothing after it.
+
+
+Ignoring Entire Files
+=====================
+
+Imagine a situation where we are adding |Flake8| to a codebase. Let's further
+imagine that with the exception of a few particularly bad files, we can add
+|Flake8| easily and move on with our lives. There are two ways to ignore the
+file:
+
+#. By explicitly adding it to our list of excluded paths (see: :option:`flake8
+   --exclude`)
+
+#. By adding ``# flake8: noqa`` to the file
+
+The former is the **recommended** way of ignoring entire files. By using our
+exclude list, we can include it in our configuration file and have one central
+place to find what files aren't included in Flake8 checks. The latter has the
+benefit that when we run |Flake8| with :option:`flake8 --disable-noqa` all of
+the errors in that file will show up without having to modify our
+configuration. Both exist so we can choose which is better for us.
+
+
+.. replacements
+.. |Flake8| replace:: :program:`Flake8`

docs/source/user/index.rst

@@ -23,6 +23,7 @@ This guide will cover all of these and the nuances for using Flake8.
     invocation
     configuration
     options
+    ignoring-errors
 
 .. config files
 .. command-line tutorial