如何格式化matplotlib中的等高线

我正在使用matplotlib生成隐式方程的图(例如y^x=x^y)。多亏了我已经得到的帮助,我已经走得很远了。我用等高线画出了这个图。我剩下的问题是如何设置等高线的格式,例如宽度、颜色,特别是zorder,其中等高线出现在我的网格线后面。当然,当绘制标准函数时,这些函数可以很好地工作。

import matplotlib.pyplot as plt 
from matplotlib.ticker import MultipleLocator, FormatStrFormatter
import numpy as np 

fig = plt.figure(1) 
ax = fig.add_subplot(111) 

# set up axis 
ax.spines['left'].set_position('zero') 
ax.spines['right'].set_color('none') 
ax.spines['bottom'].set_position('zero') 
ax.spines['top'].set_color('none') 
ax.xaxis.set_ticks_position('bottom') 
ax.yaxis.set_ticks_position('left') 

# setup x and y ranges and precision
x = np.arange(-0.5,5.5,0.01) 
y = np.arange(-0.5,5.5,0.01)

# draw a curve 
line, = ax.plot(x, x**2,zorder=100,linewidth=3,color='red') 

# draw a contour
X,Y=np.meshgrid(x,y)
F=X**Y
G=Y**X
ax.contour(X,Y,(F-G),[0],zorder=100,linewidth=3,color='green')

#set bounds 
ax.set_xbound(-1,7)
ax.set_ybound(-1,7) 

#add gridlines 
ax.xaxis.set_minor_locator(MultipleLocator(0.2)) 
ax.yaxis.set_minor_locator(MultipleLocator(0.2)) 
ax.xaxis.grid(True,'minor',linestyle='-',color='0.8')
ax.yaxis.grid(True,'minor',linestyle='-',color='0.8') 

plt.show()