Matplotlib库标注点函数annotate（）
Matplotlib库标注在⼯作有很⼤作⽤:
Annotate的构造函数为：Annotation(s, xy, xytext=None, xycoords=‘data’, textcoords=None, arrowprops=None, annotation_clip=None,
**kwargs) ⽤于绘制连接图上两点的箭头。
关键参数：
s 为注释⽂本内容
xy 为被注释的坐标点，⼆维元组形如(x,y)
xytext 为注释⽂本的坐标点，也是⼆维元组，默认与xy相同
xycoords为被注释点的坐标系属性(通常xycoords值为’data’，即以被注释的坐标点xy为参考)
Value              Description
=================  =============================================
'figure points'    Points from the lower left of the figure
'figure pixels'    Pixels from the lower left of the figure
'figure fraction'  Fraction of figure from lower left
'axes points'      Points from lower left corner of axes
'axes pixels'      Pixels from lower left corner of axes
'axes fraction'    Fraction of axes from lower left
'data'              Use the coordinate system of the object being
annotated (default)
'polar'            *(theta, r)* if not native 'data' coordinates
=================  =============================================
textcoords 设置注释⽂本的坐标系属性(textcoords 选择为相对于被注释点xy的偏移量，‘offset points’或者’offset pixels’)
arrowprops为箭头的样式，dict（字典）型数据，如果该属性⾮空，则会在注释⽂本和被注释点之间画⼀个箭头。如果不设
置’arrowstyle’关键字，则允许包含关键字width、headwidth、headlength、shrink，以下是arrowstyle的可选值
Name          Attrs
============  =============================================
``'-'``        None
``'->'``      head_length=0.4,head_width=0.2
``'-['``      widthB=1.0,lengthB=0.2,angleB=None
``'|-|'``      widthA=1.0,widthB=1.0
``'-|>'``      head_length=0.4,head_width=0.2
``'<-'``      head_length=0.4,head_width=0.2
``'<->'``      head_length=0.4,head_width=0.2
``'<|-'``      head_length=0.4,head_width=0.2
``'<|-|>'``    head_length=0.4,head_width=0.2
matplotlib中subplot``'fancy'``    head_length=0.4,head_width=0.4,tail_width=0.4
``'simple'``  head_length=0.5,head_width=0.5,tail_width=0.2
``'wedge'``    tail_width=0.3,shrink_factor=0.5
============  =============================================
两个点之间的连接路径。这由键值控制。
Angle(angleA=90, angleB=0, rad=0.0)[source]
Angle3(angleA=90, angleB=0)
Arc(angleA=0, angleB=0, armA=None, armB=None, rad=0.0)
Arc3(rad=0.0)[source]
Bar(armA=0.0, armB=0.0, fraction=0.3, angle=None)[source]
在pyplot模块（或Axes类的text⽅法get_bbox_patch/set_boxstyle("rarrow", pad=0.6)）中的text()函数接受关键字参数，并且在提供时，在⽂本周围绘制⼀个框。常⽤参数如下：
import matplotlib.pyplot as plt
import numpy as np
import matplotlib.path as mpath
import matplotlib.lines as mlines
import matplotlib.patches as mpatches
llections import PatchCollection
def label(xy, text):
y = xy[1] - 0.15  # shift y-value for label so that it's below the artist
<(xy[0], y, text, ha="center", family='sans-serif', size=14)
fig, ax = plt.subplots()
# create 3x3 grid to plot the artists
grid = np.mgrid[0.2:0.8:3j, 0.2:0.8:3j].reshape(2, -1).T
patches = []
# add a circle
circle = mpatches.Circle(grid[0], 0.1, ec="none")
patches.append(circle)
label(grid[0], "Circle")
# add a rectangle
rect = mpatches.Rectangle(grid[1] - [0.025, 0.05], 0.05, 0.1, ec="none")
patches.append(rect)
label(grid[1], "Rectangle")
# add a wedge
wedge = mpatches.Wedge(grid[2], 0.1, 30, 270, ec="none")
patches.append(wedge)
label(grid[2], "Wedge")
# add a Polygon
polygon = mpatches.RegularPolygon(grid[3], 5, 0.1)
patches.append(polygon)
label(grid[3], "Polygon")
# add an ellipse
ellipse = mpatches.Ellipse(grid[4], 0.2, 0.1)
patches.append(ellipse)
label(grid[4], "Ellipse")
# add an arrow
arrow = mpatches.Arrow(grid[5, 0] - 0.05, grid[5, 1] - 0.05, 0.1, 0.1,
width=0.1)
patches.append(arrow)
label(grid[5], "Arrow")
# add a path patch
Path = mpath.Path
path_data = [
(Path.MOVETO, [0.018, -0.11]),
(Path.CURVE4, [-0.031, -0.051]),
(Path.CURVE4, [-0.115, 0.073]),
(Path.CURVE4, [-0.03, 0.073]),
(Path.LINETO, [-0.011, 0.039]),
(Path.CURVE4, [0.043, 0.121]),
(Path.CURVE4, [0.075, -0.005]),
(Path.CURVE4, [0.035, -0.027]),
(Path.CLOSEPOLY, [0.018, -0.11])]
codes, verts = zip(*path_data)
path = mpath.Path(verts + grid[6], codes)
patch = mpatches.PathPatch(path)
patches.append(patch)
label(grid[6], "PathPatch")
# add a fancy box
fancybox = mpatches.FancyBboxPatch(
grid[7] - [0.025, 0.05], 0.05, 0.1,
boxstyle=mpatches.BoxStyle("Round", pad=0.02))
patches.append(fancybox)
label(grid[7], "FancyBboxPatch")
# add a line
x, y = np.array([[-0.06, 0.0, 0.1], [0.05, -0.05, 0.05]])
line = mlines.Line2D(x + grid[8, 0], y + grid[8, 1], lw=5., alpha=0.3)
label(grid[8], "Line2D")
colors = np.linspace(0, 1, len(patches))
collection = PatchCollection(patches, hsv, alpha=0.3)
collection.set_array(np.array(colors))
ax.add_collection(collection)
ax.add_line(line)
plt.axis('equal')
plt.axis('off')
plt.tight_layout()
plt.show()
View Code
boxstyle⽅框外形，参数是框样式的名称与其作为关键字参数的属性facecolor(简写fc)背景颜⾊
edgecolor(简写ec)边框线条颜⾊
edgewidth边框线条⼤⼩
box类名称属性
Circle        circle        pad=0.3
DArrow        darrow        pad=0.3
LArrow        larrow        pad=0.3
RArrow        rarrow        pad=0.3
Round        round        pad=0.3,rounding_size=None
Round4        round4        pad=0.3,rounding_size=None
Roundtooth    roundtooth    pad=0.3,tooth_size=None
Sawtooth    sawtooth    pad=0.3,tooth_size=None
Square        square        pad=0.3
案例
import numpy as np
import matplotlib.pylab  as plt
x = np.arange(0, 10, 0.005)
y = np.exp(-x / 2.) * np.sin(2 * np.pi * x)
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x, y)
ax.set_xlim(0, 10)
ax.set_ylim(-1, 1)
xdata, ydata = 5, 0
xdisplay, ydisplay = ansform_point((xdata, ydata))
bbox = dict(box, fc="0.8")
arrowprops = dict(arrow,connection) offset = 100
ax.annotate('data = (%.1f, %.1f)' % (xdata, ydata),
xy=(xdata, ydata), xytext=(1 * offset, offset), textcoords='offset pixels',
bbox=bbox, arrowprops=arrowprops)
disp = ax.annotate('display = (%.1f, %.1f)' % (xdisplay, ydisplay),
(xdisplay, ydisplay), xytext=(0.5 * offset, -offset),
xycoords='figure pixels',
textcoords='offset points',
bbox=bbox, arrowprops=arrowprops)
plt.show()

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