testbed/matplotlib__matplotlib/galleries/users_explain/artists/artist_intro.rst

.. _users_artists:

Introduction to Artists
-----------------------

Almost all objects you interact with on a Matplotlib plot are called "Artist"
(and are subclasses of the `.Artist` class).  :doc:`Figure <../figure/index>`
and :doc:`Axes <../axes/index>` are Artists, and generally contain
`~.axis.Axis` Artists and Artists that contain data or annotation information.


Creating Artists
~~~~~~~~~~~~~~~~

Usually we do not instantiate Artists directly, but rather use a plotting
method on `~.axes.Axes`.  Some examples of plotting methods and the Artist
object they create is given below:

=========================================  =================
Axes helper method                         Artist
=========================================  =================
`~.axes.Axes.annotate` - text annotations  `.Annotation`
`~.axes.Axes.bar` - bar charts             `.Rectangle`
`~.axes.Axes.errorbar` - error bar plots   `.Line2D` and
                                           `.Rectangle`
`~.axes.Axes.fill` - shared area           `.Polygon`
`~.axes.Axes.hist` - histograms            `.Rectangle`
`~.axes.Axes.imshow` - image data          `.AxesImage`
`~.axes.Axes.legend` - Axes legend         `.Legend`
`~.axes.Axes.plot` - xy plots              `.Line2D`
`~.axes.Axes.scatter` - scatter charts     `.PolyCollection`
`~.axes.Axes.text` - text                  `.Text`
=========================================  =================

As an example, we can save the Line2D Artist returned from `.axes.Axes.plot`:

.. sourcecode:: ipython

    In [209]: import matplotlib.pyplot as plt
    In [210]: import matplotlib.artist as martist
    In [211]: import numpy as np

    In [212]: fig, ax = plt.subplots()
    In [213]: x, y = np.random.rand(2, 100)
    In [214]: lines = ax.plot(x, y, '-', label='example')
    In [215]: print(lines)
    [<matplotlib.lines.Line2D at 0xd378b0c>]

Note that ``plot`` returns a _list_ of lines because you can pass in multiple x,
y pairs to plot.  The line has been added to the Axes, and we can retrieve the
Artist via `~.Axes.get_lines()`:

.. sourcecode:: ipython

    In [216]: print(ax.get_lines())
    <a list of 1 Line2D objects>
    In [217]: print(ax.get_lines()[0])
    Line2D(example)

Changing Artist properties
~~~~~~~~~~~~~~~~~~~~~~~~~~

Getting the ``lines`` object gives us access to all the properties of the
Line2D object.  So if we want to change the *linewidth* after the fact, we can do so using `.Artist.set`.

.. plot::
    :include-source:

    fig, ax = plt.subplots(figsize=(4, 2.5))
    x = np.arange(0, 13, 0.2)
    y = np.sin(x)
    lines = ax.plot(x, y, '-', label='example', linewidth=0.2, color='blue')
    lines[0].set(color='green', linewidth=2)

We can interrogate the full list of settable properties with
`matplotlib.artist.getp`:

.. sourcecode:: ipython

    In [218]: martist.getp(lines[0])
    agg_filter = None
    alpha = None
    animated = False
    antialiased or aa = True
    bbox = Bbox(x0=0.004013842290585101, y0=0.013914221641967...
    children = []
    clip_box = TransformedBbox(     Bbox(x0=0.0, y0=0.0, x1=1.0, ...
    clip_on = True
    clip_path = None
    color or c = blue
    dash_capstyle = butt
    dash_joinstyle = round
    data = (array([0.91377845, 0.58456834, 0.36492019, 0.0379...
    drawstyle or ds = default
    figure = Figure(550x450)
    fillstyle = full
    gapcolor = None
    gid = None
    in_layout = True
    label = example
    linestyle or ls = -
    linewidth or lw = 2.0
    marker = None
    markeredgecolor or mec = blue
    markeredgewidth or mew = 1.0
    markerfacecolor or mfc = blue
    markerfacecoloralt or mfcalt = none
    markersize or ms = 6.0
    markevery = None
    mouseover = False
    path = Path(array([[0.91377845, 0.51224793],        [0.58...
    path_effects = []
    picker = None
    pickradius = 5
    rasterized = False
    sketch_params = None
    snap = None
    solid_capstyle = projecting
    solid_joinstyle = round
    tightbbox = Bbox(x0=70.4609002763619, y0=54.321277798941786, x...
    transform = CompositeGenericTransform(     TransformWrapper(  ...
    transformed_clip_path_and_affine = (None, None)
    url = None
    visible = True
    window_extent = Bbox(x0=70.4609002763619, y0=54.321277798941786, x...
    xdata = [0.91377845 0.58456834 0.36492019 0.03796664 0.884...
    xydata = [[0.91377845 0.51224793]  [0.58456834 0.9820474 ] ...
    ydata = [0.51224793 0.9820474  0.24469912 0.61647032 0.483...
    zorder = 2

Note most Artists also have a distinct list of setters; e.g.
`.Line2D.set_color` or `.Line2D.set_linewidth`.

Changing Artist data
~~~~~~~~~~~~~~~~~~~~

In addition to styling properties like *color* and *linewidth*, the Line2D
object has a *data* property.  You can set the data after the line has been
created using `.Line2D.set_data`.  This is often used for Animations, where the
same line is shown evolving over time (see :doc:`../animations/index`)

.. plot::
    :include-source:

    fig, ax = plt.subplots(figsize=(4, 2.5))
    x = np.arange(0, 13, 0.2)
    y = np.sin(x)
    lines = ax.plot(x, y, '-', label='example')
    lines[0].set_data([x, np.cos(x)])

Manually adding Artists
~~~~~~~~~~~~~~~~~~~~~~~

Not all Artists have helper methods, or you may want to use a low-level method
for some reason.  For example the `.patches.Circle` Artist does not have a
helper, but we can still create and add to an Axes using the
`.axes.Axes.add_artist` method:

.. plot::
    :include-source:

    import matplotlib.patches as mpatches

    fig, ax = plt.subplots(figsize=(4, 2.5))
    circle = mpatches.Circle((0.5, 0.5), 0.25, ec="none")
    ax.add_artist(circle)
    clipped_circle = mpatches.Circle((1, 0.5), 0.125, ec="none", facecolor='C1')
    ax.add_artist(clipped_circle)
    ax.set_aspect(1)

The Circle takes the center and radius of the Circle as arguments to its
constructor; optional arguments are passed as keyword arguments.

Note that when we add an Artist manually like this, it doesn't necessarily
adjust the axis limits like most of the helper methods do, so the Artists can
be clipped, as is the case above for the ``clipped_circle`` patch.

See :ref:`artist_reference` for other patches.

Removing Artists
~~~~~~~~~~~~~~~~

Sometimes we want to remove an Artist from a figure without re-specifying the
whole figure from scratch.  Most Artists have a usable *remove* method that
will remove the Artist from its Axes list. For instance ``lines[0].remove()``
would remove the *Line2D* artist created in the example above.