如何确定matplotlib图例？

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
y1 = [1, 4, 9, 16]
y2 = [1, 2, 3, 4]

plt.plot(x, y1, label='y1')
plt.plot(x, y2, label='y2')

plt.legend()
plt.show()

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches

x = [1, 2, 3, 4]
y1 = [1, 4, 9, 16]
y2 = [1, 2, 3, 4]

plt.plot(x, y1)
plt.plot(x, y2)

# 自定义图例
patch1 = mpatches.Patch(color='blue', label='y1')
patch2 = mpatches.Patch(color='orange', label='y2')
plt.legend(handles=[patch1, patch2])

plt.show()

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
y1 = [1, 4, 9, 16]
y2 = [1, 2, 3, 4]

plt.plot(x, y1, label='y1')
plt.plot(x, y2, label='y2')

plt.legend(loc='upper right')
plt.show()

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
y1 = [1, 4, 9, 16]
y2 = [1, 2, 3, 4]

plt.plot(x, y1, label='y1')
plt.plot(x, y2, label='y2')

plt.legend(title='Legend')
plt.show()