plotting the diagram

plot.py

def plot_diagram(self, 
                 yvalue, 
                 xlabel, 
                 ylabel, 
                 title, 
                 filename):
    plt.figure(figsize=(8,5))
    ax = plt.gca()

    self.overall.plot(kind='line', 
                      y=yvalue, 
                      ax=ax, 
                      label="Overall", 
                      color='black')
    self.germany.plot(kind='line', 
                      y=yvalue,  
                      ax=ax, 
                      label="Germany", 
                      color='red')

    plt.xlabel(xlabel)
    plt.ylabel(ylabel)
    plt.title(title)
    plt.savefig(filename + '.png', dpi=300)
        
    return filename + '.png'