Removing cells, inputs, or outputs
==================================

.. module:: nbconvert.preprocessors

When converting Notebooks into other formats, it is possible to
remove parts of a cell, or entire cells, using preprocessors.
The notebook will remain unchanged, but the outputs will have
certain pieces removed. Here are two primary ways to accomplish
this.

Removing pieces of cells using cell tags
----------------------------------------

The most straightforward way to control which pieces of cells are
removed is to use **cell tags**. These are single-string snippets of
metadata that are stored in each cells "tag" field. The
:class:`TagRemovePreprocessor` can be used 
to remove inputs, outputs, or entire cells.

For example, here is a configuration that uses a different tag for
removing each part of a cell with the HTMLExporter. In this case,
we demonstrate using the nbconvert Python API.

.. code-block:: python

   from traitlets.config import Config
   import nbformat as nbf
   from nbconvert.exporters import HTMLExporter

   c = Config()

   # Configure our tag removal
   c.TagRemovePreprocessor.remove_cell_tags = ("remove_cell",)
   c.TagRemovePreprocessor.remove_all_outputs_tags = ('remove_output',)
   c.TagRemovePreprocessor.remove_input_tags = ('remove_input',)

   # Configure and run out exporter
   c.HTMLExporter.preprocessors = ["TagRemovePreprocessor"]
   HTMLExporter(config=c).from_filename("path/to/mynotebook.ipynb")

Removing cells using Regular Expressions on cell content
--------------------------------------------------------

Sometimes you'd rather remove cells based on their _content_ rather
than their tags. In this case, you can use the :class:`RegexRemovePreprocessor`.

You initalize this preprocessor with a single `patterns` configuration, which
is a list of strings. For each cell, this preprocessor checks whether
the cell contents match any of the strings provided in `patterns`.
If the contents match any of the patterns, the cell is removed from the notebook.

For example, execute the following command to convert a notebook to html
and remove cells containing only whitespace:

.. code-block:: bash

    jupyter nbconvert --RegexRemovePreprocessor.patterns="['\s*\Z']" mynotebook.ipynb

The command line argument sets the list of patterns to '\s*\Z' which matches
an arbitrary number of whitespace characters followed by the end of the string.

See https://regex101.com/ for an interactive guide to regular expressions
(make sure to select the python flavor). See https://docs.python.org/library/re.html
for the official regular expression documentation in python.

