import matplotlib.pyplot as plt
import numpy as np
x=np.linspace(-3,3,50)
y=2*x+1
plt.figure(num=3,figsize=(8,5)) #set the figure feature
plt.plot(x,y,color='red',linewidth=1.0)
new_ticks=np.linspace(-5,5,11)
print(new_ticks)
plt.yticks(new_ticks)
#gca='get current axis'
ax=plt.gca()
ax.spines['right'].set_color('none') #make the right line disappear
ax.spines['top'].set_color('none') #same as last line: top
ax.xaxis.set_ticks_position('bottom') #default
ax.yaxis.set_ticks_position('left')
ax.spines['bottom'].set_position(('data',0)) #outward, axes
ax.spines['left'].set_position(('data',0))
x0=1
y0=2*x0+1
plt.scatter(x0,y0,s=50,color='g') #choose the special point
plt.plot([x0,x0],[y0,0],'k--',linewidth=2.5)
#method 1
#####
plt.annotate(r'$2x+1=%s$'%y0,xy=(x0,y0),xycoords='data',xytext=(+30,-30),textcoords='offset points',fontsize=16,arrowprops=dict(arrowstyle='->',connectionstyle='arc3,rad=.2'))
#method 2
#####
# r'$  $' :regular expression
plt.text(-3.7,3,r'$This\ is\ the\ some\ text.\ \mu\ \sigma_i\ \alpha_t$',fontdict={'size':16,'color':'r'})
plt.show()