pandas.DataFrame.plot(): Labels do not appear in legend

The following code plots two lines. The column names appear in the legend.

x=np.linspace(-10,10,201)
y,z=np.sin(x),np.cos(x)
x,y,z=pd.Series(x),pd.Series(y),pd.Series(z)
df=pd.concat([x,y,z],axis=1)
df.columns=['x','sin(x)','cos(x)']
df=df.set_index('x')
df.plot()
plt.show()
plt.clf();plt.close()

However, the following equivalent code shows None as legend, even though the labels are explicitly set.

ax=df.plot(y='sin(x)',label='sin(x)')
df.plot(y='cos(x)',label='cos(x)',ax=ax)
plt.show()

Of course there are alternative ways to make this work, but it appears to me that passing the labels should suffice. In particular, I don’t think their values should be replaced with None, or printed as x-label.

[MaxGhenis]

Similar to https://github.com/pandas-dev/pandas/issues/9542#issuecomment-438580042, label is ignored when plotting a one-column DataFrame:

import pandas as pd
df = pd.DataFrame({'a': [2, 3]}, index=[0, 1])
df.plot(label='b')

df.plot(label=['b']) also doesn’t work. I’m on 0.25.3.

[zohimchandani]

Having the same issue as previously noted. Using

df[["Training Cost"]].plot(ax=axes[0,0], title = 'Training set', label = 'ADAM')

but the output plot has ‘Training cost’ as the label instead of the specified ‘ADAM’. Wondering what the fix is?