"""

The legend module defines the Legend class, which is responsible for

drawing legends associated with Axes and/or figures.

.. important::

It is unlikely that you would ever create a Legend instance manually.

Most users would normally create a legend via the `~.Axes.legend`

function. For more details on legends there is also a :ref:`legend guide

<legend_guide>`.

The `Legend` class is a container of legend handles and legend texts.

The legend handler map specifies how to create legend handles from artists

(lines, patches, etc.) in the Axes or figures. Default legend handlers are

defined in the :mod:`~matplotlib.legend_handler` module. While not all artist

types are covered by the default legend handlers, custom legend handlers can be

defined to support arbitrary objects.

See the :ref`<legend_guide>` for more

information.

"""

import itertools

import logging

import numbers

import time

import numpy as np

import matplotlib as mpl

from matplotlib import _api, _docstring, cbook, colors, offsetbox

from matplotlib.artist import Artist, allow_rasterization

from matplotlib.cbook import silent_list

from matplotlib.font_manager import FontProperties

from matplotlib.lines import Line2D

from matplotlib.patches import (Patch, Rectangle, Shadow, FancyBboxPatch,

StepPatch)

from matplotlib.collections import (

Collection, CircleCollection, LineCollection, PatchCollection, PathCollection,

PolyCollection, RegularPolyCollection)

from matplotlib.text import Text

from matplotlib.transforms import Bbox, BboxBase, TransformedBbox

from matplotlib.transforms import BboxTransformTo, BboxTransformFrom

from matplotlib.offsetbox import (

AnchoredOffsetbox, DraggableOffsetBox,

HPacker, VPacker,

DrawingArea, TextArea,

)

from matplotlib.container import ErrorbarContainer, BarContainer, StemContainer

from . import legend_handler

class DraggableLegend(DraggableOffsetBox):

def __init__(self, legend, use_blit=False, update="loc"):

"""

Wrapper around a `.Legend` to support mouse dragging.

Parameters

----------

legend : `.Legend`

The `.Legend` instance to wrap.

use_blit : bool, optional

Use blitting for faster image composition. For details see

:ref:`func-animation`.

update : {'loc', 'bbox'}, optional

If "loc", update the *loc* parameter of the legend upon finalizing.

If "bbox", update the *bbox_to_anchor* parameter.

"""

self.legend = legend

_api.check_in_list(["loc", "bbox"], update=update)

self._update = update

super().__init__(legend, legend._legend_box, use_blit=use_blit)

def finalize_offset(self):

if self._update == "loc":

self._update_loc(self.get_loc_in_canvas())

elif self._update == "bbox":

self._update_bbox_to_anchor(self.get_loc_in_canvas())

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 default bbox_to_anchor.

if bbox.width == 0 or bbox.height == 0:

self.legend.set_bbox_to_anchor(None)

bbox = self.legend.get_bbox_to_anchor()

_bbox_transform = BboxTransformFrom(bbox)

self.legend._loc = tuple(_bbox_transform.transform(loc_in_canvas))

def _update_bbox_to_anchor(self, loc_in_canvas):

loc_in_bbox = self.legend.axes.transAxes.transform(loc_in_canvas)

self.legend.set_bbox_to_anchor(loc_in_bbox)

_legend_kw_doc_base = """

bbox_to_anchor : `.BboxBase`, 2-tuple, or 4-tuple of floats

Box that is used to position the legend in conjunction with *loc*.

This is an advanced option for free placement of the legend. For

most use cases, *loc* alone is sufficient.

Defaults to ``axes.bbox`` (if called as a method to `.Axes.legend`) or

``figure.bbox`` (if ``figure.legend``).

Bbox coordinates are interpreted in the coordinate system given by

*bbox_transform*, with the default transform

Axes or Figure coordinates, depending on which ``legend`` is called.

If a 4-tuple or `.BboxBase` is given, then it specifies the bbox

``(x, y, width, height)`` that the legend is placed in.

To put the legend in the best location in the bottom right

quadrant of the Axes (or figure)::

loc='best', bbox_to_anchor=(0.5, 0., 0.5, 0.5)

A 2-tuple ``(x, y)`` places the corner of the legend specified by *loc* at

x, y. For example, to put the legend's upper right-hand corner in the

center of the Axes (or figure) the following keywords can be used::

loc='upper right', bbox_to_anchor=(0.5, 0.5)

For more details on legend positioning, see the

:ref:`legend_guide`.

ncols : int, default: 1

The number of columns that the legend has.

For backward compatibility, the spelling *ncol* is also supported

but it is discouraged. If both are given, *ncols* takes precedence.

prop : None or `~matplotlib.font_manager.FontProperties` or dict

The font properties of the legend. If None (default), the current

:data:`matplotlib.rcParams` will be used.

fontsize : int or {'xx-small', 'x-small', 'small', 'medium', 'large', \

'x-large', 'xx-large'}

The font size of the legend. If the value is numeric the size will be the

absolute font size in points. String values are relative to the current

default font size. This argument is only used if *prop* is not specified.

labelcolor : str or list, default: :rc:`legend.labelcolor`

The color of the text in the legend. Either a valid color string

(for example, 'red'), or a list of color strings. The labelcolor can

also be made to match the color of the line or marker using 'linecolor',

'markerfacecolor' (or 'mfc'), or 'markeredgecolor' (or 'mec').

Labelcolor can be set globally using :rc:`legend.labelcolor`. If None,

use :rc:`text.color`.

numpoints : int, default: :rc:`legend.numpoints`

The number of marker points in the legend when creating a legend

entry for a `.Line2D` (line).

scatterpoints : int, default: :rc:`legend.scatterpoints`

The number of marker points in the legend when creating

a legend entry for a `.PathCollection` (scatter plot).

scatteryoffsets : iterable of floats, default: ``[0.375, 0.5, 0.3125]``

The vertical offset (relative to the font size) for the markers

created for a scatter plot legend entry. 0.0 is at the base the

legend text, and 1.0 is at the top. To draw all markers at the

same height, set to ``[0.5]``.

markerscale : float, default: :rc:`legend.markerscale`

The relative size of legend markers compared to the originally drawn ones.

markerfirst : bool, default: True

If *True*, legend marker is placed to the left of the legend label.

If *False*, legend marker is placed to the right of the legend label.

reverse : bool, default: False

If *True*, the legend labels are displayed in reverse order from the input.

If *False*, the legend labels are displayed in the same order as the input.

.. versionadded:: 3.7

frameon : bool, default: :rc:`legend.frameon`

Whether the legend should be drawn on a patch (frame).

fancybox : bool, default: :rc:`legend.fancybox`

Whether round edges should be enabled around the `.FancyBboxPatch` which

makes up the legend's background.

shadow : None, bool or dict, default: :rc:`legend.shadow`

Whether to draw a shadow behind the legend.

The shadow can be configured using `.Patch` keywords.

Customization via :rc:`legend.shadow` is currently not supported.

framealpha : float, default: :rc:`legend.framealpha`

The alpha transparency of the legend's background.

If *shadow* is activated and *framealpha* is ``None``, the default value is

ignored.

facecolor : "inherit" or color, default: :rc:`legend.facecolor`

The legend's background color.

If ``"inherit"``, use :rc:`axes.facecolor`.

edgecolor : "inherit" or color, default: :rc:`legend.edgecolor`

The legend's background patch edge color.

If ``"inherit"``, use :rc:`axes.edgecolor`.

linewidth : float or None, default: :rc:`legend.linewidth`

The legend's background patch edge linewidth.

If ``None``, use :rc:`patch.linewidth`.

.. versionadded:: 3.11

mode : {"expand", None}

If *mode* is set to ``"expand"`` the legend will be horizontally

expanded to fill the Axes area (or *bbox_to_anchor* if defines

the legend's size).

bbox_transform : None or `~matplotlib.transforms.Transform`

The transform for the bounding box (*bbox_to_anchor*). For a value

of ``None`` (default) the Axes'

:data:`!matplotlib.axes.Axes.transAxes` transform will be used.

title : str or None

The legend's title. Default is no title (``None``).

title_fontproperties : None or `~matplotlib.font_manager.FontProperties` or dict

The font properties of the legend's title. If None (default), the

*title_fontsize* argument will be used if present; if *title_fontsize* is

also None, the current :rc:`legend.title_fontsize` will be used.

title_fontsize : int or {'xx-small', 'x-small', 'small', 'medium', 'large', \

'x-large', 'xx-large'}, default: :rc:`legend.title_fontsize`

The font size of the legend's title.

Note: This cannot be combined with *title_fontproperties*. If you want

to set the fontsize alongside other font properties, use the *size*

parameter in *title_fontproperties*.

alignment : {'center', 'left', 'right'}, default: 'center'

The alignment of the legend title and the box of entries. The entries

are aligned as a single block, so that markers always lined up.

borderpad : float, default: :rc:`legend.borderpad`

The fractional whitespace inside the legend border, in font-size units.

labelspacing : float, default: :rc:`legend.labelspacing`

The vertical space between the legend entries, in font-size units.

handlelength : float, default: :rc:`legend.handlelength`

The length of the legend handles, in font-size units.

handleheight : float, default: :rc:`legend.handleheight`

The height of the legend handles, in font-size units.

handletextpad : float, default: :rc:`legend.handletextpad`

The pad between the legend handle and text, in font-size units.

borderaxespad : float, default: :rc:`legend.borderaxespad`

The pad between the Axes and legend border, in font-size units.

columnspacing : float, default: :rc:`legend.columnspacing`

The spacing between columns, in font-size units.

handler_map : dict or None

The custom dictionary mapping instances or types to a legend

handler. This *handler_map* updates the default handler map

found at `matplotlib.legend.Legend.get_legend_handler_map`.

draggable : bool, default: False

Whether the legend can be dragged with the mouse.

"""

_loc_doc_base = """

loc : str or pair of floats, default: {default}

The location of the legend.

The string locations place the legend at the corresponding position

within the bounding box, which by default is the full {parent} area.

The bounding box can be changed via *bbox_to_anchor*.

The positions are visualized below::

+--------------+--------------+---------------+

| 'upper left' |'upper center'| 'upper right' |

+--------------+--------------+---------------+

|'center left' | 'center' |'center right' |

+--------------+--------------+---------------+

| 'lower left' |'lower center'| 'lower right' |

+--------------+--------------+---------------+

{best}

The location can also be a 2-tuple giving the coordinates of the lower-left

corner of the legend in {parent} coordinates (in which case *bbox_to_anchor*

will be ignored).

For back-compatibility, ``'center right'`` (but no other location) can also

be spelled ``'right'``, and each "string" location can also be given as a

numeric value:

================== =============

Location String Location Code

================== =============

'best' (Axes only) 0

'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

================== =============

{outside}"""

_loc_doc_best = """

The string ``'best'`` places the legend at the location, among the nine

locations defined so far, with the minimum overlap with other drawn

artists. This currently takes into account most, but not all, artists

added to the Axes via plotting functions. In particular it does not consider

inset axes, titles, or axis labels.

The computation of the best position can be expensive for plots with large

amounts of data. If speed becomes a concern, you may may benefit from

providing a specific location.

"""

_legend_kw_axes_st = (

_loc_doc_base.format(parent='axes', default=':rc:`legend.loc`',

best=_loc_doc_best, outside='') +

_legend_kw_doc_base)

_docstring.interpd.register(_legend_kw_axes=_legend_kw_axes_st)

_outside_doc = """

If a figure is using the constrained layout manager, the string codes

of the *loc* keyword argument can get better layout behaviour using the

prefix 'outside'. There is ambiguity at the corners, so 'outside

upper right' will make space for the legend above the rest of the

axes in the layout, and 'outside right upper' will make space on the

right side of the layout. In addition to the values of *loc*

listed above, we have 'outside right upper', 'outside right lower',

'outside left upper', and 'outside left lower'. See

:ref:`legend_guide` for more details.

"""

_legend_kw_figure_st = (

_loc_doc_base.format(parent='figure', default="'upper right'",

best='', outside=_outside_doc) +

_legend_kw_doc_base)

_docstring.interpd.register(_legend_kw_figure=_legend_kw_figure_st)

_legend_kw_both_st = (

_loc_doc_base.format(parent='axes/figure',

default=":rc:`legend.loc` for Axes, 'upper right' for Figure",

best=_loc_doc_best, outside=_outside_doc) +

_legend_kw_doc_base)

_docstring.interpd.register(_legend_kw_doc=_legend_kw_both_st)

_legend_kw_set_loc_st = (

_loc_doc_base.format(parent='axes/figure',

default=":rc:`legend.loc` for Axes, 'upper right' for Figure",

best=_loc_doc_best, outside=_outside_doc))

_docstring.interpd.register(_legend_kw_set_loc_doc=_legend_kw_set_loc_st)

class Legend(Artist):

"""

Place a legend on the figure/axes.

"""

# 'best' is only implemented for Axes legends

codes = {'best': 0, **AnchoredOffsetbox.codes}

zorder = 5

def __str__(self):

return "Legend"

@_docstring.interpd

def __init__(

self, parent, handles, labels,

*,

loc=None,

numpoints=None, # number of points in the legend line

markerscale=None, # relative size of legend markers vs. original

markerfirst=True, # left/right ordering of legend marker and label

reverse=False, # reverse ordering of legend marker and label

scatterpoints=None, # number of scatter points

scatteryoffsets=None,

prop=None, # properties for the legend texts

fontsize=None, # keyword to set font size directly

labelcolor=None, # keyword to set the text color

# spacing & pad defined as a fraction of the font-size

borderpad=None, # whitespace inside the legend border

labelspacing=None, # vertical space between the legend entries

handlelength=None, # length of the legend handles

handleheight=None, # height of the legend handles

handletextpad=None, # pad between the legend handle and text

borderaxespad=None, # pad between the Axes and legend border

columnspacing=None, # spacing between columns

ncols=1, # number of columns

mode=None, # horizontal distribution of columns: None or "expand"

fancybox=None, # True: fancy box, False: rounded box, None: rcParam

shadow=None,

title=None, # legend title

title_fontsize=None, # legend title font size

framealpha=None, # set frame alpha

edgecolor=None, # frame patch edgecolor

facecolor=None, # frame patch facecolor

linewidth=None, # frame patch linewidth

bbox_to_anchor=None, # bbox to which the legend will be anchored

bbox_transform=None, # transform for the bbox

frameon=None, # draw frame

handler_map=None,

title_fontproperties=None, # properties for the legend title

alignment="center", # control the alignment within the legend box

ncol=1, # synonym for ncols (backward compatibility)

draggable=False # whether the legend can be dragged with the mouse

):

"""

Parameters

----------

parent : `~matplotlib.axes.Axes` or `.Figure`

The artist that contains the legend.

handles : list of (`.Artist` or tuple of `.Artist`)

A list of Artists (lines, patches) to be added to the legend.

labels : list of str

A list of labels to show next to the artists. The length of handles

and labels should be the same. If they are not, they are truncated

to the length of the shorter list.

Other Parameters

----------------

%(_legend_kw_doc)s

Attributes

----------

legend_handles

List of `.Artist` objects added as legend entries.

.. versionadded:: 3.7

"""

# local import only to avoid circularity

from matplotlib.axes import Axes

from matplotlib.figure import FigureBase

super().__init__()

if prop is None:

self.prop = FontProperties(size=mpl._val_or_rc(fontsize, "legend.fontsize"))

else:

self.prop = FontProperties._from_any(prop)

if isinstance(prop, dict) and "size" not in prop:

self.prop.set_size(mpl.rcParams["legend.fontsize"])

self._fontsize = self.prop.get_size_in_points()

self.texts = []

self.legend_handles = []

self._legend_title_box = None

#: A dictionary with the extra handler mappings for this Legend

#: instance.

self._custom_handler_map = handler_map

self.numpoints = mpl._val_or_rc(numpoints, 'legend.numpoints')

self.markerscale = mpl._val_or_rc(markerscale, 'legend.markerscale')

self.scatterpoints = mpl._val_or_rc(scatterpoints, 'legend.scatterpoints')

self.borderpad = mpl._val_or_rc(borderpad, 'legend.borderpad')

self.labelspacing = mpl._val_or_rc(labelspacing, 'legend.labelspacing')

self.handlelength = mpl._val_or_rc(handlelength, 'legend.handlelength')

self.handleheight = mpl._val_or_rc(handleheight, 'legend.handleheight')

self.handletextpad = mpl._val_or_rc(handletextpad, 'legend.handletextpad')

self.borderaxespad = mpl._val_or_rc(borderaxespad, 'legend.borderaxespad')

self.columnspacing = mpl._val_or_rc(columnspacing, 'legend.columnspacing')

self.shadow = mpl._val_or_rc(shadow, 'legend.shadow')

if reverse:

labels = [*reversed(labels)]

handles = [*reversed(handles)]

handles = list(handles)

if len(handles) < 2:

ncols = 1

self._ncols = ncols if ncols != 1 else 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.])

else:

self._scatteryoffsets = np.asarray(scatteryoffsets)

reps = self.scatterpoints // len(self._scatteryoffsets) + 1

self._scatteryoffsets = np.tile(self._scatteryoffsets,

reps)[:self.scatterpoints]

# _legend_box is a VPacker 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

self.axes = parent

self.set_figure(parent.get_figure(root=False))

elif isinstance(parent, FigureBase):

self.isaxes = False

self.set_figure(parent)

else:

raise TypeError(

"Legend needs either Axes or FigureBase as parent"

)

self.parent = parent

self._mode = mode

self.set_bbox_to_anchor(bbox_to_anchor, bbox_transform)

# Figure out if self.shadow is valid

# If shadow was None, rcParams loads False

# So it shouldn't be None here

self._shadow_props = {'ox': 2, 'oy': -2} # default location offsets

if isinstance(self.shadow, dict):

self._shadow_props.update(self.shadow)

self.shadow = True

elif self.shadow in (0, 1, True, False):

self.shadow = bool(self.shadow)

else:

raise ValueError(

'Legend shadow must be a dict or bool, not '

f'{self.shadow!r} of type {type(self.shadow)}.'

)

# We use FancyBboxPatch to draw a legend frame. The location

# and size of the box will be updated during the drawing time.

facecolor = mpl._val_or_rc(facecolor, "legend.facecolor")

if facecolor == 'inherit':

facecolor = mpl.rcParams["axes.facecolor"]

edgecolor = mpl._val_or_rc(edgecolor, "legend.edgecolor")

if edgecolor == 'inherit':

edgecolor = mpl.rcParams["axes.edgecolor"]

fancybox = mpl._val_or_rc(fancybox, "legend.fancybox")

linewidth = mpl._val_or_rc(linewidth, "legend.linewidth")

self.legendPatch = FancyBboxPatch(

xy=(0, 0), width=1, height=1,

facecolor=facecolor, edgecolor=edgecolor,

linewidth=linewidth,

# If shadow is used, default to alpha=1 (#8943).

alpha=(framealpha if framealpha is not None

else 1 if shadow

else mpl.rcParams["legend.framealpha"]),

# The width and height of the legendPatch will be set (in draw())

# to the length that includes the padding. Thus we set pad=0 here.

boxstyle=("round,pad=0,rounding_size=0.2" if fancybox

else "square,pad=0"),

mutation_scale=self._fontsize,

snap=True,

visible=mpl._val_or_rc(frameon, "legend.frameon")

)

self._set_artist_props(self.legendPatch)

_api.check_in_list(["center", "left", "right"], alignment=alignment)

self._alignment = alignment

# init with null renderer

self._init_legend_box(handles, labels, markerfirst)

# Set legend location

self.set_loc(loc)

# figure out title font properties:

if title_fontsize is not None and title_fontproperties is not None:

raise ValueError(

"title_fontsize and title_fontproperties can't be specified "

"at the same time. Only use one of them. ")

title_prop_fp = FontProperties._from_any(title_fontproperties)

if isinstance(title_fontproperties, dict):

if "size" not in title_fontproperties:

title_fontsize = mpl.rcParams["legend.title_fontsize"]

title_prop_fp.set_size(title_fontsize)

elif title_fontsize is not None:

title_prop_fp.set_size(title_fontsize)

elif not isinstance(title_fontproperties, FontProperties):

title_fontsize = mpl.rcParams["legend.title_fontsize"]

title_prop_fp.set_size(title_fontsize)

self.set_title(title, prop=title_prop_fp)

self._draggable = None

self.set_draggable(state=draggable)

# set the text color

color_getters = { # getter function depends on line or patch

'linecolor': ['get_markerfacecolor',

'get_facecolor',

'get_markeredgecolor',

'get_edgecolor',

'get_color'],

'markerfacecolor': ['get_markerfacecolor', 'get_facecolor'],

'mfc': ['get_markerfacecolor', 'get_facecolor'],

'markeredgecolor': ['get_markeredgecolor', 'get_edgecolor'],

'mec': ['get_markeredgecolor', 'get_edgecolor'],

}

labelcolor = mpl._val_or_rc(mpl._val_or_rc(labelcolor, 'legend.labelcolor'),

'text.color')

if isinstance(labelcolor, str) and labelcolor in color_getters:

getter_names = color_getters[labelcolor]

for handle, text in zip(self.legend_handles, self.texts):

try:

if handle.get_array() is not None:

continue

except AttributeError:

pass

for getter_name in getter_names:

try:

color = getattr(handle, getter_name)()

except AttributeError:

continue

if isinstance(color, np.ndarray):

if color.size == 0:

continue

elif (color.shape[0] == 1 or np.isclose(color, color[0]).all()):

text.set_color(color[0])

else:

pass

elif cbook._str_lower_equal(color, 'none'):

continue

elif mpl.colors.to_rgba(color)[3] == 0:

continue

else:

text.set_color(color)

break

elif cbook._str_equal(labelcolor, 'none'):

for text in self.texts:

text.set_color(labelcolor)

elif np.iterable(labelcolor):

for text, color in zip(self.texts,

itertools.cycle(

colors.to_rgba_array(labelcolor))):

text.set_color(color)

else:

raise ValueError(f"Invalid labelcolor: {labelcolor!r}")

def _set_artist_props(self, a):

"""

Set the boilerplate props for artists added to Axes.

"""

a.set_figure(self.get_figure(root=False))

if self.isaxes:

a.axes = self.axes

a.set_transform(self.get_transform())

@_docstring.interpd

def set_loc(self, loc=None):

"""

Set the location of the legend.

.. versionadded:: 3.8

Parameters

----------

%(_legend_kw_set_loc_doc)s

"""

loc0 = loc

self._loc_used_default = loc is None

if loc is None:

loc = mpl.rcParams["legend.loc"]

if not self.isaxes and loc in [0, 'best']:

loc = 'upper right'

type_err_message = ("loc must be string, coordinate tuple, or"

f" an integer 0-10, not {loc!r}")

# handle outside legends:

self._outside_loc = None

if isinstance(loc, str):

if loc.split()[0] == 'outside':

# strip outside:

loc = loc.split('outside ')[1]

# strip "center" at the beginning

self._outside_loc = loc.replace('center ', '')

# strip first

self._outside_loc = self._outside_loc.split()[0]

locs = loc.split()

if len(locs) > 1 and locs[0] in ('right', 'left'):

# locs doesn't accept "left upper", etc, so swap

if locs[0] != 'center':

locs = locs[::-1]

loc = locs[0] + ' ' + locs[1]

# check that loc is in acceptable strings

loc = _api.getitem_checked(self.codes, loc=loc)

elif np.iterable(loc):

# coerce iterable into tuple

loc = tuple(loc)

# validate the tuple represents Real coordinates

if len(loc) != 2 or not all(isinstance(e, numbers.Real) for e in loc):

raise ValueError(type_err_message)

elif isinstance(loc, int):

# validate the integer represents a string numeric value

if loc < 0 or loc > 10:

raise ValueError(type_err_message)

else:

# all other cases are invalid values of loc

raise ValueError(type_err_message)

if self.isaxes and self._outside_loc:

raise ValueError(

f"'outside' option for loc='{loc0}' keyword argument only "

"works for figure legends")

if not self.isaxes and loc == 0:

raise ValueError(

"Automatic legend placement (loc='best') not implemented for "

"figure legend")

tmp = self._loc_used_default

self._set_loc(loc)

self._loc_used_default = tmp # ignore changes done by _set_loc

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_used_default = False

self._loc_real = loc

self.stale = True

self._legend_box.set_offset(self._findoffset)

def set_ncols(self, ncols):

"""Set the number of columns."""

self._ncols = ncols

def _get_loc(self):

return self._loc_real

_loc = property(_get_loc, _set_loc)

def _findoffset(self, width, height, xdescent, ydescent, renderer):

"""Helper function to locate the legend."""

if self._loc == 0: # "best".

x, y = self._find_best_position(width, height, renderer)

elif self._loc in Legend.codes.values(): # Fixed location.

bbox = Bbox.from_bounds(0, 0, width, height)

x, y = self._get_anchored_bbox(self._loc, bbox,

self.get_bbox_to_anchor(),

renderer)

else: # 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

return x + xdescent, y + ydescent

@allow_rasterization

def draw(self, renderer):

# docstring inherited

if not self.get_visible():

return

renderer.open_group('legend', gid=self.get_gid())

fontsize = renderer.points_to_pixels(self._fontsize)

# if mode == fill, set the width of the legend_box to the

# width of the parent (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)

# update the location and size of the legend. This needs to

# be done in any case to clip the figure right.

bbox = self._legend_box.get_window_extent(renderer)

self.legendPatch.set_bounds(bbox.bounds)

self.legendPatch.set_mutation_scale(fontsize)

# self.shadow is validated in __init__

# So by here it is a bool and self._shadow_props contains any configs

if self.shadow:

Shadow(self.legendPatch, **self._shadow_props).draw(renderer)

self.legendPatch.draw(renderer)

self._legend_box.draw(renderer)

renderer.close_group('legend')

self.stale = False

# _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(),

StepPatch: legend_handler.HandlerStepPatch(),

LineCollection: legend_handler.HandlerLineCollection(),

RegularPolyCollection: legend_handler.HandlerRegularPolyCollection(),

CircleCollection: legend_handler.HandlerCircleCollection(),

BarContainer: legend_handler.HandlerPatch(

update_func=legend_handler.update_from_first_child),

tuple: legend_handler.HandlerTuple(),

PatchCollection: legend_handler.HandlerPolyCollection(),

PathCollection: legend_handler.HandlerPathCollection(),

PolyCollection: legend_handler.HandlerPolyCollection()

}

# (get|set|update)_default_handler_maps are public interfaces to

# modify the default handler map.

@classmethod

def get_default_handler_map(cls):

"""Return the global default handler map, shared by all legends."""

return cls._default_handler_map

@classmethod

def set_default_handler_map(cls, handler_map):

"""Set the global default handler map, shared by all legends."""

cls._default_handler_map = handler_map

@classmethod

def update_default_handler_map(cls, handler_map):

"""Update the global default handler map, shared by all legends."""

cls._default_handler_map.update(handler_map)

def get_legend_handler_map(self):

"""Return this legend instance's handler map."""

default_handler_map = self.get_default_handler_map()

return ({**default_handler_map, **self._custom_handler_map}

if self._custom_handler_map else default_handler_map)

@staticmethod

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_handler_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``.

"""

try:

return legend_handler_map[orig_handle]

except (TypeError, KeyError): # TypeError if unhashable.

pass

for handle_type in type(orig_handle).mro():

try:

return legend_handler_map[handle_type]

except KeyError:

pass

return None

def _init_legend_box(self, handles, labels, markerfirst=True):

"""

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 a HPacker packed with:

# - handlebox: a DrawingArea which contains the legend handle.

# - labelbox: a TextArea which contains the legend text.

text_list = [] # the list of text instances

handle_list = [] # the list of handle instances

handles_and_labels = []

# The approximate height and descent of text. These values are

# only used for plotting the legend handle.

descent = 0.35 * fontsize * (self.handleheight - 0.7) # heuristic.

height = fontsize * 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_transform(). If the artist does not use its

# default transform (e.g., Collections), you need to

# manually set their transform to the self.get_transform().

legend_handler_map = self.get_legend_handler_map()

for orig_handle, label in zip(handles, labels):

handler = self.get_legend_handler(legend_handler_map, orig_handle)

if handler is None:

_api.warn_external(

"Legend does not support handles for "

f"{type(orig_handle).__name__} "

"instances.\nA proxy artist may be used "

"instead.\nSee: https://matplotlib.org/"

"stable/users/explain/axes/legend_guide.html"

"#controlling-the-legend-entries")

# No handle for this artist, so we just defer to None.

handle_list.append(None)

else:

textbox = TextArea(label, multilinebaseline=True,

textprops=dict(

verticalalignment='baseline',

horizontalalignment='left',

fontproperties=self.prop))

handlebox = DrawingArea(width=self.handlelength * fontsize,

height=height,

xdescent=0., ydescent=descent)

text_list.append(textbox._text)

# Create the artist for the legend which represents the

# original artist/handle.

handle_list.append(handler.legend_artist(self, orig_handle,

fontsize, handlebox))

handles_and_labels.append((handlebox, textbox))

columnbox = []

# array_split splits n handles_and_labels into ncols columns, with the

# first n%ncols columns having an extra entry. filter(len, ...)

# handles the case where n < ncols: the last ncols-n columns are empty

# and get filtered out.

for handles_and_labels_column in filter(

len, np.array_split(handles_and_labels, self._ncols)):

# pack handlebox and labelbox into itembox

itemboxes = [HPacker(pad=0,

sep=self.handletextpad * fontsize,

children=[h, t] if markerfirst else [t, h],

align="baseline")

for h, t in handles_and_labels_column]

# pack columnbox

alignment = "baseline" if markerfirst else "right"

columnbox.append(VPacker(pad=0,

sep=self.labelspacing * fontsize,

align=alignment,

children=itemboxes))

mode = "expand" if self._mode == "expand" else "fixed"

sep = self.columnspacing * fontsize

self._legend_handle_box = HPacker(pad=0,

sep=sep, align="baseline",

mode=mode,

children=columnbox)

self._legend_title_box = TextArea("")

self._legend_box = VPacker(pad=self.borderpad * fontsize,

sep=self.labelspacing * fontsize,

align=self._alignment,

children=[self._legend_title_box,

self._legend_handle_box])

self._legend_box.set_figure(self.get_figure(root=False))

self._legend_box.axes = self.axes

self.texts = text_list

self.legend_handles = handle_list

def _auto_legend_data(self, renderer):

"""

Return display coordinates for hit testing for "best" positioning.

Returns

-------

bboxes

List of bounding boxes of all patches.

lines

List of `.Path` corresponding to each line.

offsets

List of (x, y) offsets of all collection.

"""

assert self.isaxes # always holds, as this is only called internally

bboxes = []

lines = []

offsets = []

for artist in self.parent._children:

if isinstance(artist, Line2D):

lines.append(

artist.get_transform().transform_path(artist.get_path()))

elif isinstance(artist, Rectangle):

bboxes.append(

artist.get_bbox().transformed(artist.get_data_transform()))

elif isinstance(artist, Patch):

lines.append(

artist.get_transform().transform_path(artist.get_path()))

elif isinstance(artist, PolyCollection):

lines.extend(artist.get_transform().transform_path(path)

for path in artist.get_paths())

elif isinstance(artist, Collection):

transform, transOffset, hoffsets, _ = artist._prepare_points()