I'm trying basic plot with two y-axis and one x-axis. To obtain the legend information for different curve I'm getting AttributeError.
Here is my code:

```
import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 2.0*np.pi, 101)
y = np.sin(x)
z = np.sinh(x)

# separate the figure object and axes object from the plotting object
fig, ax1 = plt.subplots()

# Duplicate the axes with a differebt y axis and the same x axis
ax2 = ax1.twinx()  # ax2 and ax1 will have common x axis and different y axis

# plot the curves on axes 1, and 2 and get the curve hadles
curve1 = ax1.plot(x, y, label="sin", color='r')
curve2 = ax2.plot(x, z, label="sinh", color='b')

# Make a curves list to access the parameters in the curves
curves = [curve1, curve2]

# Add legend via axes1 or axex 2 object.
# ax1.legend() will not display the legend of ax2
# ax2.legend() will not display the legend of ax1

ax1.legend(curves, [curve.get_label() for curve in curves])
#ax2.legend(curves, [curve.get_label() for curve in curves]) also valid

# Global figure properties
plt.title("Plot of sine and hyperbolic sine")
plt.show()

```

I'm getting Error on below line:

```
ax1.legend(curves, [curve.get_label() for curve in curves])

```

Please let me know if anyone know why its happening.