matplotlib · timhoffm · Feb 1, 2021 · Sep 22, 2020 · Oct 20, 2020 · Oct 20, 2020
diff --git a/doc/_static/mpl.css b/doc/_static/mpl.css
@@ -89,7 +89,7 @@ table.highlighttable td {
     padding: 0 0.5em 0 0.5em;
 }
 
-cite, code, tt {
+cite, code, tt, dl.value-list dt {
     font-family: 'Consolas', 'Deja Vu Sans Mono', 'Bitstream Vera Sans Mono', monospace;
     font-size: 0.95em;
     letter-spacing: 0.01em;
@@ -730,7 +730,6 @@ td.field-body table.property-table tr:last-of-type td {
     border-bottom-color: #888;
 }
 
-
 /* function and class description */
 .descclassname {
     color: #aaa;
@@ -806,6 +805,22 @@ dl.class > dd {
     font-size: 14px;
 }
 
+/* custom tables for lists of allowed values in "mpl._types" */
+dl.value-list {
+    display: grid;
+}
+
+dl.value-list dt {
+    grid-column: 1;
+    margin: 4px 0;
+}
+
+dl.value-list dd {
+    grid-column: 2;
+    margin: 4px 0 4px 20px;
+    padding: 0;
+}
+
 /* parameter section table */
 table.docutils.field-list {
     width: 100%;
@@ -1257,4 +1272,4 @@ div.bullet-box li {
 
 div#gallery.section .sphx-glr-clear:first-of-type, div#tutorials.section .sphx-glr-clear:first-of-type{
     display: none;
-}
+}
diff --git a/doc/api/_enums.rst b/doc/api/_enums.rst
@@ -0,0 +1,15 @@
+**********************
+``matplotlib._enums``
+**********************
+
+.. automodule:: matplotlib._enums
+   :no-members:
+
+   .. autoclass:: JoinStyle
+      :members: demo
+      :exclude-members: bevel, miter, round, input_description
+
+   .. autoclass:: CapStyle
+      :members: demo
+      :exclude-members: butt, round, projecting, input_description
+
diff --git a/doc/api/index.rst b/doc/api/index.rst
@@ -89,6 +89,7 @@ Matplotlib consists of the following submodules:
    dates_api.rst
    docstring_api.rst
    dviread.rst
+   _enums.rst
    figure_api.rst
    font_manager_api.rst
    fontconfig_pattern_api.rst

diff --git a/examples/lines_bars_and_markers/capstyle.py b/examples/lines_bars_and_markers/capstyle.py
@@ -0,0 +1,15 @@
+"""
+=========
+CapStyle
+=========
+
+The `matplotlib._enums.CapStyle` controls how Matplotlib draws the corners
+where two different line segments meet. For more details, see the
+`~matplotlib._enums.CapStyle` docs.
+"""
+
+import matplotlib.pyplot as plt
+from matplotlib._enums import CapStyle
+
+CapStyle.demo()
+plt.show()
diff --git a/examples/lines_bars_and_markers/joinstyle.py b/examples/lines_bars_and_markers/joinstyle.py
@@ -1,90 +1,15 @@
 """
-==========================
-Join styles and cap styles
-==========================
+=========
+JoinStyle
+=========
 
-This example demonstrates the available join styles and cap styles.
-
-Both are used in `.Line2D` and various ``Collections`` from
-`matplotlib.collections` as well as some functions that create these, e.g.
-`~matplotlib.pyplot.plot`.
-
-
-Join styles
-===========
-
-Join styles define how the connection between two line segments is drawn.
-
-See the respective ``solid_joinstyle``, ``dash_joinstyle`` or ``joinstyle``
-parameters.
+The `matplotlib._enums.JoinStyle` controls how Matplotlib draws the corners
+where two different line segments meet. For more details, see the
+`~matplotlib._enums.JoinStyle` docs.
 """
 
-import numpy as np
 import matplotlib.pyplot as plt
+from matplotlib._enums import JoinStyle
 
-
-def plot_angle(ax, x, y, angle, style):
-    phi = np.radians(angle)
-    xx = [x + .5, x, x + .5*np.cos(phi)]
-    yy = [y, y, y + .5*np.sin(phi)]
-    ax.plot(xx, yy, lw=12, color='tab:blue', solid_joinstyle=style)
-    ax.plot(xx, yy, lw=1, color='black')
-    ax.plot(xx[1], yy[1], 'o', color='tab:red', markersize=3)
-
-
-fig, ax = plt.subplots(figsize=(8, 6))
-ax.set_title('Join style')
-
-for x, style in enumerate(['miter', 'round', 'bevel']):
-    ax.text(x, 5, style)
-    for y, angle in enumerate([20, 45, 60, 90, 120]):
-        plot_angle(ax, x, y, angle, style)
-        if x == 0:
-            ax.text(-1.3, y, f'{angle} degrees')
-ax.text(1, 4.7, '(default)')
-
-ax.set_xlim(-1.5, 2.75)
-ax.set_ylim(-.5, 5.5)
-ax.set_axis_off()
+JoinStyle.demo()
 plt.show()
-
-
-#############################################################################
-#
-# Cap styles
-# ==========
-#
-# Cap styles define how the the end of a line is drawn.
-#
-# See the respective ``solid_capstyle``, ``dash_capstyle`` or ``capstyle``
-# parameters.
-
-fig, ax = plt.subplots(figsize=(8, 2))
-ax.set_title('Cap style')
-
-for x, style in enumerate(['butt', 'round', 'projecting']):
-    ax.text(x+0.25, 1, style, ha='center')
-    xx = [x, x+0.5]
-    yy = [0, 0]
-    ax.plot(xx, yy, lw=12, color='tab:blue', solid_capstyle=style)
-    ax.plot(xx, yy, lw=1, color='black')
-    ax.plot(xx, yy, 'o', color='tab:red', markersize=3)
-ax.text(2.25, 0.7, '(default)', ha='center')
-
-ax.set_ylim(-.5, 1.5)
-ax.set_axis_off()
-
-
-#############################################################################
-#
-# ------------
-#
-# References
-# """"""""""
-#
-# The use of the following functions, methods, classes and modules is shown
-# in this example:
-
-import matplotlib
-matplotlib.axes.Axes.plot
-matplotlib.pyplot.plot
diff --git a/lib/matplotlib/_enums.py b/lib/matplotlib/_enums.py
@@ -0,0 +1,208 @@
+"""
+Enums representing sets of strings that Matplotlib uses as input parameters.
+
+Matplotlib often uses simple data types like strings or tuples to define a
+concept; e.g. the line capstyle can be specified as one of 'butt', 'round',
+or 'projecting'. The classes in this module are used internally and serve to
+document these concepts formally.
+
+As an end-user you will not use these classes directly, but only the values
+they define.
+"""
+
+from enum import Enum, auto
+from matplotlib import cbook, docstring
+
+
+class _AutoStringNameEnum(Enum):
+    """Automate the ``name = 'name'`` part of making a (str, Enum)."""
+
+    def _generate_next_value_(name, start, count, last_values):
+        return name
+
+    def __hash__(self):
+        return str(self).__hash__()
+
+
+def _deprecate_case_insensitive_join_cap(s):
+    s_low = s.lower()
+    if s != s_low:
+        if s_low in ['miter', 'round', 'bevel']:
+            cbook.warn_deprecated(
+                "3.3", message="Case-insensitive capstyles are deprecated "
+                "since %(since)s and support for them will be removed "
+                "%(removal)s; please pass them in lowercase.")
+        elif s_low in ['butt', 'round', 'projecting']:
+            cbook.warn_deprecated(
+                "3.3", message="Case-insensitive joinstyles are deprecated "
+                "since %(since)s and support for them will be removed "
+                "%(removal)s; please pass them in lowercase.")
+        # Else, error out at the check_in_list stage.
+    return s_low
+
+
+class JoinStyle(str, _AutoStringNameEnum):
+    """
+    Define how the connection between two line segments is drawn.
+
+    For a visual impression of each *JoinStyle*, `view these docs online
+    <JoinStyle>`, or run `JoinStyle.demo`.
+
+    Lines in Matplotlib are typically defined by a 1D `~.path.Path` and a
+    finite ``linewidth``, where the underlying 1D `~.path.Path` represents the
+    center of the stroked line.
+
+    By default, `~.backend_bases.GraphicsContextBase` defines the boundaries of
+    a stroked line to simply be every point within some radius,
+    ``linewidth/2``, away from any point of the center line. However, this
+    results in corners appearing "rounded", which may not be the desired
+    behavior if you are drawing, for example, a polygon or pointed star.
+
+    **Supported values:**
+
+    .. rst-class:: value-list
+
+        'miter'
+            the "arrow-tip" style. Each boundary of the filled-in area will
+            extend in a straight line parallel to the tangent vector of the
+            centerline at the point it meets the corner, until they meet in a
+            sharp point.
+        'round'
+            stokes every point within a radius of ``linewidth/2`` of the center
+            lines.
+        'bevel'
+            the "squared-off" style. It can be thought of as a rounded corner
+            where the "circular" part of the corner has been cut off.
+
+    .. note::
+
+        Very long miter tips are cut off (to form a *bevel*) after a
+        backend-dependent limit called the "miter limit", which specifies the
+        maximum allowed ratio of miter length to line width. For example, the
+        PDF backend uses the default value of 10 specified by the PDF standard,
+        while the SVG backend does not even specify the miter limit, resulting
+        in a default value of 4 per the SVG specification. Matplotlib does not
+        currently allow the user to adjust this parameter.
+
+        A more detailed description of the effect of a miter limit can be found
+        in the `Mozilla Developer Docs
+        <https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/stroke-miterlimit>`_
+
+    .. plot::
+        :alt: Demo of possible JoinStyle's
+
+        from matplotlib._enums import JoinStyle
+        JoinStyle.demo()
+
+    """
+
+    miter = auto()
+    round = auto()
+    bevel = auto()
+
+    def __init__(self, s):
+        s = _deprecate_case_insensitive_join_cap(s)
+        Enum.__init__(self)
+
+    @staticmethod
+    def demo():
+        """Demonstrate how each JoinStyle looks for various join angles."""
+        import numpy as np
+        import matplotlib.pyplot as plt
+
+        def plot_angle(ax, x, y, angle, style):
+            phi = np.radians(angle)
+            xx = [x + .5, x, x + .5*np.cos(phi)]
+            yy = [y, y, y + .5*np.sin(phi)]
+            ax.plot(xx, yy, lw=12, color='tab:blue', solid_joinstyle=style)
+            ax.plot(xx, yy, lw=1, color='black')
+            ax.plot(xx[1], yy[1], 'o', color='tab:red', markersize=3)
+
+        fig, ax = plt.subplots(figsize=(5, 4), constrained_layout=True)
+        ax.set_title('Join style')
+        for x, style in enumerate(['miter', 'round', 'bevel']):
+            ax.text(x, 5, style)
+            for y, angle in enumerate([20, 45, 60, 90, 120]):
+                plot_angle(ax, x, y, angle, style)
+                if x == 0:
+                    ax.text(-1.3, y, f'{angle} degrees')
+        ax.set_xlim(-1.5, 2.75)
+        ax.set_ylim(-.5, 5.5)
+        ax.set_axis_off()
+        fig.show()
+
+
+JoinStyle.input_description = "{" \
+        + ", ".join([f"'{js.name}'" for js in JoinStyle]) \
+        + "}"
+
+
+class CapStyle(str, _AutoStringNameEnum):
+    r"""
+    Define how the two endpoints (caps) of an unclosed line are drawn.
+
+    How to draw the start and end points of lines that represent a closed curve
+    (i.e. that end in a `~.path.Path.CLOSEPOLY`) is controlled by the line's
+    `JoinStyle`. For all other lines, how the start and end points are drawn is
+    controlled by the *CapStyle*.
+
+    For a visual impression of each *CapStyle*, `view these docs online
+    <CapStyle>` or run `CapStyle.demo`.
+
+    **Supported values:**
+
+    .. rst-class:: value-list
+
+        'butt'
+            the line is squared off at its endpoint.
+        'projecting'
+            the line is squared off as in *butt*, but the filled in area
+            extends beyond the endpoint a distance of ``linewidth/2``.
+        'round'
+            like *butt*, but a semicircular cap is added to the end of the
+            line, of radius ``linewidth/2``.
+
+    .. plot::
+        :alt: Demo of possible CapStyle's
+
+        from matplotlib._enums import CapStyle
+        CapStyle.demo()
+
+    """
+    butt = 'butt'
+    projecting = 'projecting'
+    round = 'round'
+
+    def __init__(self, s):
+        s = _deprecate_case_insensitive_join_cap(s)
+        Enum.__init__(self)
+
+    @staticmethod
+    def demo():
+        """Demonstrate how each CapStyle looks for a thick line segment."""
+        import matplotlib.pyplot as plt
+
+        fig = plt.figure(figsize=(4, 1.2))
+        ax = fig.add_axes([0, 0, 1, 0.8])
+        ax.set_title('Cap style')
+
+        for x, style in enumerate(['butt', 'round', 'projecting']):
+            ax.text(x+0.25, 0.85, style, ha='center')
+            xx = [x, x+0.5]
+            yy = [0, 0]
+            ax.plot(xx, yy, lw=12, color='tab:blue', solid_capstyle=style)
+            ax.plot(xx, yy, lw=1, color='black')
+            ax.plot(xx, yy, 'o', color='tab:red', markersize=3)
+        ax.text(2.25, 0.55, '(default)', ha='center')
+
+        ax.set_ylim(-.5, 1.5)
+        ax.set_axis_off()
+        fig.show()
+
+
+CapStyle.input_description = "{" \
+        + ", ".join([f"'{cs.name}'" for cs in CapStyle]) \
+        + "}"
+
+docstring.interpd.update({'JoinStyle': JoinStyle.input_description,
+                          'CapStyle': CapStyle.input_description})