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The legend module defines the Legend class, which is responsible for
drawing legends associated with axes and/or figures.
The Legend class can be considered as a container of legend handles
and legend texts. Creation of corresponding legend handles from the
plot elements in the axes or figures (e.g., lines, patches, etc.) are
specified by the handler map, which defines the mapping between the
plot elements and the legend handlers to be used (the default legend
handlers are defined in the :mod:`~matplotlib.legend_handler` module). Note
that not all kinds of artist are supported by the legend yet (See
:ref:`plotting-guide-legend` for more information).
from __future__ import division, print_function
import warnings
import numpy as np
from matplotlib import rcParams
from matplotlib.artist import Artist, allow_rasterization
from matplotlib.cbook import is_string_like, iterable, silent_list, safezip
from matplotlib.font_manager import FontProperties
from matplotlib.lines import Line2D
from matplotlib.patches import Patch, Rectangle, Shadow, FancyBboxPatch
from matplotlib.collections import LineCollection, RegularPolyCollection, \
CircleCollection, PathCollection
from matplotlib.transforms import Bbox, BboxBase, TransformedBbox
from matplotlib.transforms import BboxTransformTo, BboxTransformFrom
from matplotlib.offsetbox import HPacker, VPacker, TextArea, DrawingArea
from matplotlib.offsetbox import DraggableOffsetBox
from matplotlib.container import ErrorbarContainer, BarContainer, StemContainer
from matplotlib import MatplotlibDeprecationWarning as mplDeprecation
import legend_handler
class DraggableLegend(DraggableOffsetBox):
def __init__(self, legend, use_blit=False, update="loc"):
update : If "loc", update *loc* parameter of
legend upon finalizing. If "bbox", update
*bbox_to_anchor* parameter.
self.legend = legend
if update in ["loc", "bbox"]:
self._update = update
raise ValueError("update parameter '%s' is not supported." %
DraggableOffsetBox.__init__(self, legend, legend._legend_box,
def artist_picker(self, legend, evt):
return self.legend.contains(evt)
def finalize_offset(self):
loc_in_canvas = self.get_loc_in_canvas()
if self._update == "loc":
elif self._update == "bbox":
raise RuntimeError("update parameter '%s' is not supported." %
def _update_loc(self, loc_in_canvas):
bbox = self.legend.get_bbox_to_anchor()
# if bbox has zero width or height, the transformation is
# ill-defined. Fall back to the defaul bbox_to_anchor.
if bbox.width == 0 or bbox.height == 0:
bbox = self.legend.get_bbox_to_anchor()
_bbox_transform = BboxTransformFrom(bbox)
self.legend._loc = tuple(
def _update_bbox_to_anchor(self, loc_in_canvas):
tr = self.legend.axes.transAxes
loc_in_bbox = tr.transform_point(loc_in_canvas)
class Legend(Artist):
Place a legend on the axes at location loc. Labels are a
sequence of strings and loc can be a string or an integer
specifying the legend location
The location codes are::
'best' : 0, (only implemented for axis legends)
'upper right' : 1,
'upper left' : 2,
'lower left' : 3,
'lower right' : 4,
'right' : 5,
'center left' : 6,
'center right' : 7,
'lower center' : 8,
'upper center' : 9,
'center' : 10,
loc can be a tuple of the normalized coordinate values with
respect its parent.
codes = {'best': 0, # only implemented for axis legends
'upper right': 1,
'upper left': 2,
'lower left': 3,
'lower right': 4,
'right': 5,
'center left': 6,
'center right': 7,
'lower center': 8,
'upper center': 9,
'center': 10,
zorder = 5
def __str__(self):
return "Legend"
def __init__(self, parent, handles, labels,
numpoints=None, # the number of points in the legend line
markerscale=None, # the relative size of legend markers
# vs. original
scatterpoints=3, # TODO: may be an rcParam
prop=None, # properties for the legend texts
fontsize=None, # keyword to set font size directly
# the following dimensions are in axes coords
pad=None, # deprecated; use borderpad
labelsep=None, # deprecated; use labelspacing
handlelen=None, # deprecated; use handlelength
handletextsep=None, # deprecated; use handletextpad
axespad=None, # deprecated; use borderaxespad
# spacing & pad defined as a fraction of the font-size
borderpad=None, # the whitespace inside the legend border
labelspacing=None, # the vertical space between the legend
# entries
handlelength=None, # the length of the legend handles
handleheight=None, # the height of the legend handles
handletextpad=None, # the pad between the legend handle
# and text
borderaxespad=None, # the pad between the axes and legend
# border
columnspacing=None, # spacing between columns
ncol=1, # number of columns
mode=None, # mode for horizontal distribution of columns.
# None, "expand"
fancybox=None, # True use a fancy box, false use a rounded
# box, none use rc
title=None, # set a title for the legend
bbox_to_anchor=None, # bbox that the legend will be anchored.
bbox_transform=None, # transform for the bbox
frameon=None, # draw frame
- *parent*: the artist that contains the legend
- *handles*: a list of artists (lines, patches) to be added to the
- *labels*: a list of strings to label the legend
Optional keyword arguments:
================ ====================================================
Keyword Description
================ ====================================================
loc a location code
prop the font property
fontsize the font size (used only if prop is not specified)
markerscale the relative size of legend markers vs. original
numpoints the number of points in the legend for line
scatterpoints the number of points in the legend for scatter plot
scatteryoffsets a list of yoffsets for scatter symbols in legend
frameon if True, draw a frame around the legend.
If None, use rc
fancybox if True, draw a frame with a round fancybox.
If None, use rc
shadow if True, draw a shadow behind legend
ncol number of columns
borderpad the fractional whitespace inside the legend border
labelspacing the vertical space between the legend entries
handlelength the length of the legend handles
handleheight the length of the legend handles
handletextpad the pad between the legend handle and text
borderaxespad the pad between the axes and legend border
columnspacing the spacing between columns
title the legend title
bbox_to_anchor the bbox that the legend will be anchored.
bbox_transform the transform for the bbox. transAxes if None.
================ ====================================================
The pad and spacing parameters are measured in font-size units. E.g.,
a fontsize of 10 points and a handlelength=5 implies a handlelength of
50 points. Values from rcParams will be used if None.
Users can specify any arbitrary location for the legend using the
*bbox_to_anchor* keyword argument. bbox_to_anchor can be an instance
of BboxBase(or its derivatives) or a tuple of 2 or 4 floats.
See :meth:`set_bbox_to_anchor` for more detail.
The legend location can be specified by setting *loc* with a tuple of
2 floats, which is interpreted as the lower-left corner of the legend
in the normalized axes coordinate.
# local import only to avoid circularity
from matplotlib.axes import Axes
from matplotlib.figure import Figure
if prop is None:
if fontsize is not None:
self.prop = FontProperties(size=fontsize)
self.prop = FontProperties(size=rcParams["legend.fontsize"])
elif isinstance(prop, dict):
self.prop = FontProperties(**prop)
if "size" not in prop:
self.prop = prop
self._fontsize = self.prop.get_size_in_points()
propnames = ["numpoints", "markerscale", "shadow", "columnspacing",
"scatterpoints", "handleheight"]
self.texts = []
self.legendHandles = []
self._legend_title_box = None
self._handler_map = handler_map
localdict = locals()
for name in propnames:
if localdict[name] is None:
value = rcParams["legend." + name]
value = localdict[name]
setattr(self, name, value)
# Take care the deprecated keywords
deprecated_kwds = {"pad": "borderpad",
"labelsep": "labelspacing",
"handlelen": "handlelength",
"handletextsep": "handletextpad",
"axespad": "borderaxespad"}
# convert values of deprecated keywords (ginve in axes coords)
# to new vaules in a fraction of the font size
# conversion factor
bbox = parent.bbox
axessize_fontsize = min(bbox.width, bbox.height) / self._fontsize
for k, v in deprecated_kwds.iteritems():
# use deprecated value if not None and if their newer
# counter part is None.
if localdict[k] is not None and localdict[v] is None:
warnings.warn("Use '%s' instead of '%s'." % (v, k),
setattr(self, v, localdict[k] * axessize_fontsize)
# Otherwise, use new keywords
if localdict[v] is None:
setattr(self, v, rcParams["legend." + v])
setattr(self, v, localdict[v])
del localdict
handles = list(handles)
if len(handles) < 2:
ncol = 1
self._ncol = ncol
if self.numpoints <= 0:
raise ValueError("numpoints must be > 0; it was %d" % numpoints)
# introduce y-offset for handles of the scatter plot
if scatteryoffsets is None:
self._scatteryoffsets = np.array([3. / 8., 4. / 8., 2.5 / 8.])
self._scatteryoffsets = np.asarray(scatteryoffsets)
reps = int(self.scatterpoints / len(self._scatteryoffsets)) + 1
self._scatteryoffsets = np.tile(self._scatteryoffsets,
# _legend_box is an OffsetBox instance that contains all
# legend items and will be initialized from _init_legend_box()
# method.
self._legend_box = None
if isinstance(parent, Axes):
self.isaxes = True
elif isinstance(parent, Figure):
self.isaxes = False
raise TypeError("Legend needs either Axes or Figure as parent")
self.parent = parent
if loc is None:
loc = rcParams["legend.loc"]
if not self.isaxes and loc in [0, 'best']:
loc = 'upper right'
if is_string_like(loc):
if loc not in
if self.isaxes:
warnings.warn('Unrecognized location "%s". Falling back '
'on "best"; valid locations are\n\t%s\n'
% (loc, '\n\t'.join(
loc = 0
warnings.warn('Unrecognized location "%s". Falling back '
'on "upper right"; '
'valid locations are\n\t%s\n'
% (loc, '\n\t'.join(
loc = 1
loc =[loc]
if not self.isaxes and loc == 0:
warnings.warn('Automatic legend placement (loc="best") not '
'implemented for figure legend. '
'Falling back on "upper right".')
loc = 1
self._mode = mode
self.set_bbox_to_anchor(bbox_to_anchor, bbox_transform)
# We use FancyBboxPatch to draw a legend frame. The location
# and size of the box will be updated during the drawing time.
self.legendPatch = FancyBboxPatch(
xy=(0.0, 0.0), width=1., height=1.,
# The width and height of the legendPatch will be set (in the
# draw()) to the length that includes the padding. Thus we set
# pad=0 here.
if fancybox is None:
fancybox = rcParams["legend.fancybox"]
if fancybox:
self.legendPatch.set_boxstyle("round", pad=0,
self.legendPatch.set_boxstyle("square", pad=0)
self._drawFrame = frameon
if frameon is None:
self._drawFrame = rcParams["legend.frameon"]
# init with null renderer
self._init_legend_box(handles, labels)
self._loc = loc
self._last_fontsize_points = self._fontsize
self._draggable = None
def _set_artist_props(self, a):
set the boilerplate props for artists added to axes
if self.isaxes:
def _set_loc(self, loc):
# find_offset function will be provided to _legend_box and
# _legend_box will draw itself at the location of the return
# value of the find_offset.
self._loc_real = loc
if loc == 0:
_findoffset = self._findoffset_best
_findoffset = self._findoffset_loc
#def findoffset(width, height, xdescent, ydescent):
# return _findoffset(width, height, xdescent, ydescent, renderer)
self._loc_real = loc
def _get_loc(self):
return self._loc_real
_loc = property(_get_loc, _set_loc)
def _findoffset_best(self, width, height, xdescent, ydescent, renderer):
"Helper function to locate the legend at its best position"
ox, oy = self._find_best_position(width, height, renderer)
return ox + xdescent, oy + ydescent
def _findoffset_loc(self, width, height, xdescent, ydescent, renderer):
"Helper function to locate the legend using the location code"
if iterable(self._loc) and len(self._loc) == 2:
# when loc is a tuple of axes(or figure) coordinates.
fx, fy = self._loc
bbox = self.get_bbox_to_anchor()
x, y = bbox.x0 + bbox.width * fx, bbox.y0 + bbox.height * fy
bbox = Bbox.from_bounds(0, 0, width, height)
x, y = self._get_anchored_bbox(self._loc, bbox,
return x + xdescent, y + ydescent
def draw(self, renderer):
"Draw everything that belongs to the legend"
if not self.get_visible():
fontsize = renderer.points_to_pixels(self._fontsize)
# if mode == fill, set the width of the legend_box to the
# width of the paret (minus pads)
if self._mode in ["expand"]:
pad = 2 * (self.borderaxespad + self.borderpad) * fontsize
self._legend_box.set_width(self.get_bbox_to_anchor().width - pad)
if self._drawFrame:
# update the location and size of the legend
bbox = self._legend_box.get_window_extent(renderer)
self.legendPatch.set_bounds(bbox.x0, bbox.y0,
bbox.width, bbox.height)
if self.shadow:
shadow = Shadow(self.legendPatch, 2, -2)
def _approx_text_height(self, renderer=None):
Return the approximate height of the text. This is used to place
the legend handle.
if renderer is None:
return self._fontsize
return renderer.points_to_pixels(self._fontsize)
# _default_handler_map defines the default mapping between plot
# elements and the legend handlers.
_default_handler_map = {
StemContainer: legend_handler.HandlerStem(),
ErrorbarContainer: legend_handler.HandlerErrorbar(),
Line2D: legend_handler.HandlerLine2D(),
Patch: legend_handler.HandlerPatch(),
LineCollection: legend_handler.HandlerLineCollection(),
RegularPolyCollection: legend_handler.HandlerRegularPolyCollection(),
CircleCollection: legend_handler.HandlerCircleCollection(),
BarContainer: legend_handler.HandlerPatch(
tuple: legend_handler.HandlerTuple(),
PathCollection: legend_handler.HandlerPathCollection()
# (get|set|update)_default_handler_maps are public interfaces to
# modify the defalut handler map.
def get_default_handler_map(cls):
A class method that returns the default handler map.
return cls._default_handler_map
def set_default_handler_map(cls, handler_map):
A class method to set the default handler map.
cls._default_handler_map = handler_map
def update_default_handler_map(cls, handler_map):
A class method to update the default handler map.
def get_legend_handler_map(self):
return the handler map.
default_handler_map = self.get_default_handler_map()
if self._handler_map:
hm = default_handler_map.copy()
return hm
return default_handler_map
def get_legend_handler(legend_handler_map, orig_handle):
return a legend handler from *legend_handler_map* that
corresponds to *orig_handler*.
*legend_handler_map* should be a dictionary object (that is
returned by the get_legend_handler_map method).
It first checks if the *orig_handle* itself is a key in the
*legend_hanler_map* and return the associated value.
Otherwise, it checks for each of the classes in its
method-resolution-order. If no matching key is found, it
returns None.
legend_handler_keys = legend_handler_map.keys()
if orig_handle in legend_handler_keys:
handler = legend_handler_map[orig_handle]
for handle_type in type(orig_handle).mro():
if handle_type in legend_handler_map:
handler = legend_handler_map[handle_type]
handler = None
return handler
def _init_legend_box(self, handles, labels):
Initialize the legend_box. The legend_box is an instance of
the OffsetBox, which is packed with legend handles and
texts. Once packed, their location is calculated during the
drawing time.
fontsize = self._fontsize
# legend_box is a HPacker, horizontally packed with
# columns. Each column is a VPacker, vertically packed with
# legend items. Each legend item is HPacker packed with
# legend handleBox and labelBox. handleBox is an instance of
# offsetbox.DrawingArea which contains legend handle. labelBox
# is an instance of offsetbox.TextArea which contains legend
# text.
text_list = [] # the list of text instances
handle_list = [] # the list of text instances
label_prop = dict(verticalalignment='baseline',
labelboxes = []
handleboxes = []
# The approximate height and descent of text. These values are
# only used for plotting the legend handle.
descent = 0.35 * self._approx_text_height() * (self.handleheight - 0.7)
# 0.35 and 0.7 are just heuristic numbers. this may need to be improbed
height = self._approx_text_height() * self.handleheight - descent
# each handle needs to be drawn inside a box of (x, y, w, h) =
# (0, -descent, width, height). And their coordinates should
# be given in the display coordinates.
# The transformation of each handle will be automatically set
# to self.get_trasnform(). If the artist does not uses its
# default trasnform (eg, Collections), you need to
# manually set their transform to the self.get_transform().
legend_handler_map = self.get_legend_handler_map()
for orig_handle, lab in zip(handles, labels):
handler = self.get_legend_handler(legend_handler_map, orig_handle)
if handler is None:
"Legend does not support %s\nUse proxy artist "
"\n" %
textbox = TextArea(lab, textprops=label_prop,
multilinebaseline=True, minimumdescent=True)
handlebox = DrawingArea(width=self.handlelength * fontsize,
xdescent=0., ydescent=descent)
handle = handler(self, orig_handle,
#xdescent, ydescent, width, height,
if len(handleboxes) > 0:
# We calculate number of rows in each column. The first
# (num_largecol) columns will have (nrows+1) rows, and remaining
# (num_smallcol) columns will have (nrows) rows.
ncol = min(self._ncol, len(handleboxes))
nrows, num_largecol = divmod(len(handleboxes), ncol)
num_smallcol = ncol - num_largecol
# starting index of each column and number of rows in it.
largecol = safezip(range(0,
num_largecol * (nrows + 1),
(nrows + 1)),
[nrows + 1] * num_largecol)
smallcol = safezip(range(num_largecol * (nrows + 1),
[nrows] * num_smallcol)
largecol, smallcol = [], []
handle_label = safezip(handleboxes, labelboxes)
columnbox = []
for i0, di in largecol + smallcol:
# pack handleBox and labelBox into itemBox
itemBoxes = [HPacker(pad=0,
sep=self.handletextpad * fontsize,
children=[h, t], align="baseline")
for h, t in handle_label[i0:i0 + di]]
# minimumdescent=False for the text of the last row of the column
# pack columnBox
sep=self.labelspacing * fontsize,
if self._mode == "expand":
mode = "expand"
mode = "fixed"
sep = self.columnspacing * fontsize
self._legend_handle_box = HPacker(pad=0,
sep=sep, align="baseline",
self._legend_title_box = TextArea("")
self._legend_box = VPacker(pad=self.borderpad * fontsize,
sep=self.labelspacing * fontsize,
self.texts = text_list
self.legendHandles = handle_list
def _auto_legend_data(self):
Returns list of vertices and extents covered by the plot.
Returns a two long list.
First element is a list of (x, y) vertices (in
display-coordinates) covered by all the lines and line
collections, in the legend's handles.
Second element is a list of bounding boxes for all the patches in
the legend's handles.
# should always hold because function is only called internally
assert self.isaxes
ax = self.parent
bboxes = []
lines = []
for handle in ax.lines:
assert isinstance(handle, Line2D)
path = handle.get_path()
trans = handle.get_transform()
tpath = trans.transform_path(path)
for handle in ax.patches:
assert isinstance(handle, Patch)
if isinstance(handle, Rectangle):
transform = handle.get_data_transform()
transform = handle.get_transform()
vertices = np.concatenate([l.vertices for l in lines])
except ValueError:
vertices = np.array([])
return [vertices, bboxes, lines]
def draw_frame(self, b):
'b is a boolean. Set draw frame to b'
def get_children(self):
'return a list of child artists'
children = []
if self._legend_box:
if self._legend_title_box:
return children
def get_frame(self):
'return the Rectangle instance used to frame the legend'
return self.legendPatch
def get_lines(self):
'return a list of lines.Line2D instances in the legend'
return [h for h in self.legendHandles if isinstance(h, Line2D)]
def get_patches(self):
'return a list of patch instances in the legend'
return silent_list('Patch',
[h for h in self.legendHandles
if isinstance(h, Patch)])
def get_texts(self):
'return a list of text.Text instance in the legend'
return silent_list('Text', self.texts)
def set_title(self, title, prop=None):
set the legend title. Fontproperties can be optionally set
with *prop* parameter.
if prop is not None:
if isinstance(prop, dict):
prop = FontProperties(**prop)
if title:
def get_title(self):
'return Text instance for the legend title'
return self._legend_title_box._text
def get_window_extent(self, *args, **kwargs):
'return a extent of the the legend'
return self.legendPatch.get_window_extent(*args, **kwargs)
def get_frame_on(self):
Get whether the legend box patch is drawn
return self._drawFrame
def set_frame_on(self, b):
Set whether the legend box patch is drawn
ACCEPTS: [ *True* | *False* ]
self._drawFrame = b
def get_bbox_to_anchor(self):
return the bbox that the legend will be anchored
if self._bbox_to_anchor is None:
return self.parent.bbox
return self._bbox_to_anchor
def set_bbox_to_anchor(self, bbox, transform=None):
set the bbox that the legend will be anchored.
*bbox* can be a BboxBase instance, a tuple of [left, bottom,
width, height] in the given transform (normalized axes
coordinate if None), or a tuple of [left, bottom] where the
width and height will be assumed to be zero.
if bbox is None:
self._bbox_to_anchor = None
elif isinstance(bbox, BboxBase):
self._bbox_to_anchor = bbox
l = len(bbox)
except TypeError:
raise ValueError("Invalid argument for bbox : %s" % str(bbox))
if l == 2:
bbox = [bbox[0], bbox[1], 0, 0]
self._bbox_to_anchor = Bbox.from_bounds(*bbox)
if transform is None:
transform = BboxTransformTo(self.parent.bbox)
self._bbox_to_anchor = TransformedBbox(self._bbox_to_anchor,
def _get_anchored_bbox(self, loc, bbox, parentbbox, renderer):
Place the *bbox* inside the *parentbbox* according to a given
location code. Return the (x,y) coordinate of the bbox.
- loc: a location code in range(1, 11).
This corresponds to the possible values for self._loc, excluding
- bbox: bbox to be placed, display coodinate units.
- parentbbox: a parent box which will contain the bbox. In
display coordinates.
assert loc in range(1, 11) # called only internally
BEST, UR, UL, LL, LR, R, CL, CR, LC, UC, C = range(11)
anchor_coefs = {UR: "NE",
UL: "NW",
LL: "SW",
LR: "SE",
R: "E",
CL: "W",
CR: "E",
LC: "S",
UC: "N",
C: "C"}
c = anchor_coefs[loc]
fontsize = renderer.points_to_pixels(self._fontsize)
container = parentbbox.padded(-(self.borderaxespad) * fontsize)
anchored_box = bbox.anchored(c, container=container)
return anchored_box.x0, anchored_box.y0
def _find_best_position(self, width, height, renderer, consider=None):
Determine the best location to place the legend.
`consider` is a list of (x, y) pairs to consider as a potential
lower-left corner of the legend. All are display coords.
# should always hold because function is only called internally
assert self.isaxes
verts, bboxes, lines = self._auto_legend_data()
bbox = Bbox.from_bounds(0, 0, width, height)
if consider is None:
consider = [self._get_anchored_bbox(x, bbox,
for x in range(1, len(]
#tx, ty = self.legendPatch.get_x(), self.legendPatch.get_y()
candidates = []
for l, b in consider:
legendBox = Bbox.from_bounds(l, b, width, height)
badness = 0
# XXX TODO: If markers are present, it would be good to
# take their into account when checking vertex overlaps in
# the next line.
badness = legendBox.count_contains(verts)
badness += legendBox.count_overlaps(bboxes)
for line in lines:
# FIXME: the following line is ill-suited for lines
# that 'spiral' around the center, because the bbox
# may intersect with the legend even if the line
# itself doesn't. One solution would be to break up
# the line into its straight-segment components, but
# this may (or may not) result in a significant
# slowdown if lines with many vertices are present.
if line.intersects_bbox(legendBox):
badness += 1
ox, oy = l, b
if badness == 0:
return ox, oy
candidates.append((badness, (l, b)))
# rather than use min() or list.sort(), do this so that we are assured
# that in the case of two equal badnesses, the one first considered is
# returned.
# NOTE: list.sort() is stable.But leave as it is for now. -JJL
minCandidate = candidates[0]
for candidate in candidates:
if candidate[0] < minCandidate[0]:
minCandidate = candidate
ox, oy = minCandidate[1]
return ox, oy
def contains(self, event):
return self.legendPatch.contains(event)
def draggable(self, state=None, use_blit=False, update="loc"):
Set the draggable state -- if state is
* None : toggle the current state
* True : turn draggable on
* False : turn draggable off
If draggable is on, you can drag the legend on the canvas with
the mouse. The DraggableLegend helper instance is returned if
draggable is on.
The update parameter control which parameter of the legend changes
when dragged. If update is "loc", the *loc* paramter of the legend
is changed. If "bbox", the *bbox_to_anchor* parameter is changed.
is_draggable = self._draggable is not None
# if state is None we'll toggle
if state is None:
state = not is_draggable
if state:
if self._draggable is None:
self._draggable = DraggableLegend(self,
if self._draggable is not None:
self._draggable = None
return self._draggable
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