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</ul>
</li>
<li class="toc-h3 nav-item toc-entry">
<a class="reference internal nav-link" href="#parsing">
Parsing
</a>
</li>
<li class="toc-h3 nav-item toc-entry">
<a class="reference internal nav-link" href="#visitor-pattern-for-matplotlib-figure">
Visitor pattern for matplotlib figure
</a>
</li>
</ul>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#backward-compatibility">
Backward compatibility
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#alternatives">
Alternatives
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#appendix">
Appendix
</a>
<ul class="nav section-nav flex-column">
<li class="toc-h3 nav-item toc-entry">
<a class="reference internal nav-link" href="#matplotlib-primitives">
Matplotlib primitives
</a>
</li>
</ul>
</li>
</ul>
</nav>
</div>
<div class="toc-item">
</div>
</div>
<main class="col-12 col-md-9 col-xl-7 py-md-5 pl-md-5 pr-md-4 bd-content" role="main">
<div>
<section id="mep26-artist-styling">
<h1>MEP26: Artist styling<a class="headerlink" href="#mep26-artist-styling" title="Permalink to this headline">#</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#status" id="id1">Status</a></p></li>
<li><p><a class="reference internal" href="#branches-and-pull-requests" id="id2">Branches and Pull requests</a></p></li>
<li><p><a class="reference internal" href="#abstract" id="id3">Abstract</a></p></li>
<li><p><a class="reference internal" href="#detailed-description" id="id4">Detailed description</a></p></li>
<li><p><a class="reference internal" href="#implementation" id="id5">Implementation</a></p>
<ul>
<li><p><a class="reference internal" href="#bnf-grammar" id="id6">BNF Grammar</a></p></li>
<li><p><a class="reference internal" href="#syntax" id="id7">Syntax</a></p>
<ul>
<li><p><a class="reference internal" href="#selectors" id="id8">Selectors</a></p></li>
<li><p><a class="reference internal" href="#gid-selector" id="id9">GID selector</a></p></li>
<li><p><a class="reference internal" href="#attributes-and-values" id="id10">Attributes and values</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#parsing" id="id11">Parsing</a></p></li>
<li><p><a class="reference internal" href="#visitor-pattern-for-matplotlib-figure" id="id12">Visitor pattern for matplotlib figure</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#backward-compatibility" id="id13">Backward compatibility</a></p></li>
<li><p><a class="reference internal" href="#alternatives" id="id14">Alternatives</a></p></li>
<li><p><a class="reference internal" href="#appendix" id="id15">Appendix</a></p>
<ul>
<li><p><a class="reference internal" href="#matplotlib-primitives" id="id16">Matplotlib primitives</a></p></li>
</ul>
</li>
</ul>
</div>
<section id="status">
<h2><a class="toc-backref" href="#id1">Status</a><a class="headerlink" href="#status" title="Permalink to this headline">#</a></h2>
<p><strong>Rejected</strong></p>
</section>
<section id="branches-and-pull-requests">
<h2><a class="toc-backref" href="#id2">Branches and Pull requests</a><a class="headerlink" href="#branches-and-pull-requests" title="Permalink to this headline">#</a></h2>
</section>
<section id="abstract">
<h2><a class="toc-backref" href="#id3">Abstract</a><a class="headerlink" href="#abstract" title="Permalink to this headline">#</a></h2>
<p>This MEP proposes a new stylesheet implementation to allow more
comprehensive and dynamic styling of artists.</p>
<p>The current version of matplotlib (1.4.0) allows stylesheets based on
the rcParams syntax to be applied before creation of a plot. The
methodology below proposes a new syntax, based on CSS, which would
allow styling of individual artists and properties, which can be
applied dynamically to existing objects.</p>
<p>This is related to (and makes steps toward) the overall goal of moving
to a DOM/tree-like architecture.</p>
</section>
<section id="detailed-description">
<h2><a class="toc-backref" href="#id4">Detailed description</a><a class="headerlink" href="#detailed-description" title="Permalink to this headline">#</a></h2>
<p>Currently, the look and appearance of existing artist objects (figure,
axes, Line2D etc...) can only be updated via <code class="docutils literal notranslate"><span class="pre">set_</span></code> and <code class="docutils literal notranslate"><span class="pre">get_</span></code> methods
on the artist object, which is quite laborious, especially if no
reference to the artist(s) has been stored. The new style sheets
introduced in 1.4 allow styling before a plot is created, but do not
offer any means to dynamically update plots or distinguish between
artists of the same type (i.e. to specify the <code class="docutils literal notranslate"><span class="pre">line</span> <span class="pre">color</span></code> and <code class="docutils literal notranslate"><span class="pre">line</span>
<span class="pre">style</span></code> separately for differing <a class="reference internal" href="../../api/_as_gen/matplotlib.lines.Line2D.html#matplotlib.lines.Line2D" title="matplotlib.lines.Line2D"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Line2D</span></code></a> objects).</p>
<p>The initial development should concentrate on allowing styling of
artist primitives (those <a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a>s that do not contain other
<a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a>s), and further development could expand the CSS syntax rules
and parser to allow more complex styling. See the appendix for a list
of primitives.</p>
<p>The new methodology would require development of a number of steps:</p>
<ul class="simple">
<li><p>A new stylesheet syntax (likely based on CSS) to allow selection of
artists by type, class, id etc...</p></li>
<li><p>A mechanism by which to parse a stylesheet into a tree</p></li>
<li><p>A mechanism by which to translate the parse-tree into something
which can be used to update the properties of relevant
artists. Ideally this would implement a method by which to traverse
the artists in a tree-like structure.</p></li>
<li><p>A mechanism by which to generate a stylesheet from existing artist
properties. This would be useful to allow a user to export a
stylesheet from an existing figure (where the appearance may have
been set using the matplotlib API)...</p></li>
</ul>
</section>
<section id="implementation">
<h2><a class="toc-backref" href="#id5">Implementation</a><a class="headerlink" href="#implementation" title="Permalink to this headline">#</a></h2>
<p>It will be easiest to allow a '3rd party' to modify/set the style of an artist
if the 'style' is created as a separate class and store against the artist as a
property. The <a class="reference internal" href="../../api/backend_bases_api.html#matplotlib.backend_bases.GraphicsContextBase" title="matplotlib.backend_bases.GraphicsContextBase"><code class="xref py py-obj docutils literal notranslate"><span class="pre">GraphicsContextBase</span></code></a> class already provides a the basis of a
<code class="docutils literal notranslate"><span class="pre">Style</span></code> class and an artist's <a class="reference internal" href="../../api/_as_gen/matplotlib.artist.Artist.draw.html#matplotlib.artist.Artist.draw" title="matplotlib.artist.Artist.draw"><code class="xref py py-obj docutils literal notranslate"><span class="pre">draw</span></code></a> method can be refactored to use
the <code class="docutils literal notranslate"><span class="pre">Style</span></code> class rather than setting up its own <a class="reference internal" href="../../api/backend_bases_api.html#matplotlib.backend_bases.GraphicsContextBase" title="matplotlib.backend_bases.GraphicsContextBase"><code class="xref py py-obj docutils literal notranslate"><span class="pre">GraphicsContextBase</span></code></a> and
transferring its style-related properties to it. A minimal example of how this
could be implemented is shown here: <a class="reference external" href="https://github.com/JamesRamm/mpl_experiment">https://github.com/JamesRamm/mpl_experiment</a></p>
<p>IMO, this will also make the API and code base much neater as
individual get/set methods for artist style properties are now
redundant... Indirectly related would be a general drive to replace
get/set methods with properties. Implementing the style class with
properties would be a big stride toward this...</p>
<p>For initial development, I suggest developing a syntax based on a much
(much much) simplified version of CSS. I am in favour of dubbing this
Artist Style Sheets :+1: :</p>
<section id="bnf-grammar">
<h3><a class="toc-backref" href="#id6">BNF Grammar</a><a class="headerlink" href="#bnf-grammar" title="Permalink to this headline">#</a></h3>
<p>I propose a very simple syntax to implement initially (like a proof of
concept), which can be expanded upon in the future. The BNF form of
the syntax is given below and then explained</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">RuleSet</span> <span class="p">:</span><span class="o">:=</span> <span class="n">SelectorSequence</span> <span class="s2">"{"</span><span class="n">Declaration</span><span class="s2">"}"</span>
<span class="n">SelectorSequence</span> <span class="p">::</span> <span class="o">=</span> <span class="n">Selector</span> <span class="p">{</span><span class="s2">","</span> <span class="n">Selector</span><span class="p">}</span>
<span class="n">Declaration</span> <span class="p">:</span><span class="o">:=</span> <span class="n">propName</span><span class="s2">":"</span> <span class="n">propValue</span><span class="s2">";"</span>
<span class="n">Selector</span> <span class="p">:</span><span class="o">:=</span> <span class="n">ArtistIdent</span><span class="p">{</span><span class="s2">"#"</span><span class="n">Ident</span><span class="p">}</span>
<span class="n">propName</span> <span class="p">:</span><span class="o">:=</span> <span class="n">Ident</span>
<span class="n">propValue</span> <span class="p">:</span><span class="o">:=</span> <span class="n">Ident</span> <span class="o">|</span> <span class="n">Number</span> <span class="o">|</span> <span class="n">Colour</span> <span class="o">|</span> <span class="s2">"None"</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">ArtistIdent</span></code>, <code class="docutils literal notranslate"><span class="pre">Ident</span></code>, <code class="docutils literal notranslate"><span class="pre">Number</span></code> and <code class="docutils literal notranslate"><span class="pre">Colour</span></code> are tokens (the basic
building blocks of the expression) which are defined by regular
expressions.</p>
</section>
<section id="syntax">
<h3><a class="toc-backref" href="#id7">Syntax</a><a class="headerlink" href="#syntax" title="Permalink to this headline">#</a></h3>
<p>A CSS stylesheet consists of a series of <strong>rule sets</strong> in hierarchical
order (rules are applied from top to bottom). Each rule follows the
syntax</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">selector</span> <span class="p">{</span><span class="n">attribute</span><span class="p">:</span> <span class="n">value</span><span class="p">;}</span>
</pre></div>
</div>
<p>Each rule can have any number of <code class="docutils literal notranslate"><span class="pre">attribute:</span> <span class="pre">value</span></code> pairs, and a
stylesheet can have any number of rules.</p>
<p>The initial syntax is designed only for <a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a> primitives. It does
not address the question of how to set properties on <a class="reference internal" href="../../api/container_api.html#matplotlib.container.Container" title="matplotlib.container.Container"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Container</span></code></a> types
(whose properties may themselves be <a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a>s with settable
properties), however, a future solution to this could simply be nested
<code class="docutils literal notranslate"><span class="pre">RuleSet</span></code>s</p>
<section id="selectors">
<h4><a class="toc-backref" href="#id8">Selectors</a><a class="headerlink" href="#selectors" title="Permalink to this headline">#</a></h4>
<p>Selectors define the object to which the attribute updates should be
applied. As a starting point, I propose just 2 selectors to use in
initial development:</p>
<p>Artist Type Selector</p>
<p>Select an <a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a> by it's type. E.g <a class="reference internal" href="../../api/_as_gen/matplotlib.lines.Line2D.html#matplotlib.lines.Line2D" title="matplotlib.lines.Line2D"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Line2D</span></code></a> or <a class="reference internal" href="../../api/text_api.html#matplotlib.text.Text" title="matplotlib.text.Text"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Text</span></code></a>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Line2D</span> <span class="p">{</span><span class="n">attribute</span><span class="p">:</span> <span class="n">value</span><span class="p">}</span>
</pre></div>
</div>
<p>The regex for matching the artist type selector (<code class="docutils literal notranslate"><span class="pre">ArtistIdent</span></code> in the BNF grammar) would be:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ArtistIdent</span> <span class="o">=</span> <span class="sa">r</span><span class="s1">'(?P<ArtistIdent>\bLine2D\b|\bText\b|\bAxesImage\b|\bFigureImage\b|\bPatch\b)'</span>
</pre></div>
</div>
</section>
<section id="gid-selector">
<h4><a class="toc-backref" href="#id9">GID selector</a><a class="headerlink" href="#gid-selector" title="Permalink to this headline">#</a></h4>
<p>Select an <a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a> by its <code class="docutils literal notranslate"><span class="pre">gid</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Line2D</span><span class="c1">#myGID {attribute: value}</span>
</pre></div>
</div>
<p>A <code class="docutils literal notranslate"><span class="pre">gid</span></code> can be any string, so the regex could be as follows:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Ident</span> <span class="o">=</span> <span class="sa">r</span><span class="s1">'(?P<Ident>[a-zA-Z_][a-zA-Z_0-9]*)'</span>
</pre></div>
</div>
<p>The above selectors roughly correspond to their CSS counterparts
(<a class="reference external" href="http://www.w3.org/TR/CSS21/selector.html">http://www.w3.org/TR/CSS21/selector.html</a>)</p>
</section>
<section id="attributes-and-values">
<h4><a class="toc-backref" href="#id10">Attributes and values</a><a class="headerlink" href="#attributes-and-values" title="Permalink to this headline">#</a></h4>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">Attributes</span></code> are any valid (settable) property for the <a class="reference internal" href="../../api/artist_api.html#matplotlib.artist.Artist" title="matplotlib.artist.Artist"><code class="xref py py-obj docutils literal notranslate"><span class="pre">Artist</span></code></a> in question.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">Values</span></code> are any valid value for the property (Usually a string, or number).</p></li>
</ul>
</section>
</section>
<section id="parsing">
<h3><a class="toc-backref" href="#id11">Parsing</a><a class="headerlink" href="#parsing" title="Permalink to this headline">#</a></h3>
<p>Parsing would consist of breaking the stylesheet into tokens (the
python cookbook gives a nice tokenizing recipe on page 66), applying
the syntax rules and constructing a <code class="docutils literal notranslate"><span class="pre">Tree</span></code>. This requires defining the
grammar of the stylesheet (again, we can borrow from CSS) and writing
a parser. Happily, there is a recipe for this in the python cookbook
as well.</p>
</section>
<section id="visitor-pattern-for-matplotlib-figure">
<h3><a class="toc-backref" href="#id12">Visitor pattern for matplotlib figure</a><a class="headerlink" href="#visitor-pattern-for-matplotlib-figure" title="Permalink to this headline">#</a></h3>
<p>In order to apply the stylesheet rules to the relevant artists, we
need to 'visit' each artist in a figure and apply the relevant rule.
Here is a visitor class (again, thanks to python cookbook), where each
<code class="docutils literal notranslate"><span class="pre">node</span></code> would be an artist in the figure. A <code class="docutils literal notranslate"><span class="pre">visit_</span></code> method would need
to be implemented for each mpl artist, to handle the different
properties for each</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Visitor</span><span class="p">:</span>
<span class="k">def</span> <span class="nf">visit</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">node</span><span class="p">):</span>
<span class="n">name</span> <span class="o">=</span> <span class="s1">'visit_'</span> <span class="o">+</span> <span class="nb">type</span><span class="p">(</span><span class="n">node</span><span class="p">)</span><span class="o">.</span><span class="vm">__name__</span>
<span class="n">meth</span> <span class="o">=</span> <span class="nb">getattr</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="kc">None</span><span class="p">)</span>
<span class="k">if</span> <span class="n">meth</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">NotImplementedError</span>
<span class="k">return</span> <span class="n">meth</span><span class="p">(</span><span class="n">node</span><span class="p">)</span>
</pre></div>
</div>
<p>An <code class="docutils literal notranslate"><span class="pre">evaluator</span></code> class would then take the stylesheet rules and
implement the visitor on each one of them.</p>
</section>
</section>
<section id="backward-compatibility">
<h2><a class="toc-backref" href="#id13">Backward compatibility</a><a class="headerlink" href="#backward-compatibility" title="Permalink to this headline">#</a></h2>
<p>Implementing a separate <code class="docutils literal notranslate"><span class="pre">Style</span></code> class would break backward
compatibility as many get/set methods on an artist would become
redundant. While it would be possible to alter these methods to hook
into the <code class="docutils literal notranslate"><span class="pre">Style</span></code> class (stored as a property against the artist), I
would be in favor of simply removing them to both neaten/simplify the
codebase and to provide a simple, uncluttered API...</p>
</section>
<section id="alternatives">
<h2><a class="toc-backref" href="#id14">Alternatives</a><a class="headerlink" href="#alternatives" title="Permalink to this headline">#</a></h2>
<p>No alternatives, but some of the ground covered here overlaps with
MEP25, which may assist in this development</p>
</section>
<section id="appendix">
<h2><a class="toc-backref" href="#id15">Appendix</a><a class="headerlink" href="#appendix" title="Permalink to this headline">#</a></h2>
<section id="matplotlib-primitives">
<h3><a class="toc-backref" href="#id16">Matplotlib primitives</a><a class="headerlink" href="#matplotlib-primitives" title="Permalink to this headline">#</a></h3>
<p>This will form the initial selectors which stylesheets can use.</p>
<ul class="simple">
<li><p>Line2D</p></li>
<li><p>Text</p></li>
<li><p>AxesImage</p></li>
<li><p>FigureImage</p></li>
<li><p>Patch</p></li>
</ul>
</section>
</section>
</section>
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