Ahh!! okay, I understand your question now.
Since the method is
DataFrame.plot, the DataFrame supplied becomes the input for the plot function, after which only the column names via strings can be accessed.
Here is a work around for what you want to achieve -
women_degrees[‘Biology_men’] = 100 - women_degrees[‘Biology’]
fig, ax = plt.subplots()
women_degrees.plot(x= ‘Year’, y= ‘Biology’, ax= ax, c= ‘b’, label= ‘Women’)
women_degrees.plot(x= ‘Year’, y= ‘Biology_men’, ax= ax, c= ‘g’, label= ‘Men’)
This will plot two lines on the same figure. Only drawback is that you would have to create a new column in the DataFrame. I know this doesn’t exactly achieve what you wanted to do, but you can try this out once.