Legend label is not adding for multiple plots in python

Question

I wanted to read 5 csv files. I have the following function which plots the graphs separately and I wanted to add a legend to to each plot. However, I am getting this warning the legend is not being added to the plots even if i have a label added to my function.

UserWarning: No labelled objects found. Use label='...' kwarg on individual plots. warnings.warn("No labelled objects found. "

import pandas as pd
import matplotlib.pyplot as plt


df1 = pd.read_csv('test1.csv')
df2 = pd.read_csv('test2.csv')
df3 = pd.read_csv('test3.csv')
df4 = pd.read_csv('test4.csv')
df5 = pd.read_csv('test5.csv')


def runplot(df, title, label):   
    rows, cols = df.shape

    fig, ax = plt.subplots()
    ax.plot(df['price'].values, df['cost'].values)
    ax.legend()


    plt.title(title)
    plt.annotate('test!', 
                 xy=(rows, df.ix[rows-1,'cost']),  
                 xycoords='data',
                 xytext=(-30,30),
                 textcoords='offset points',
                 arrowprops=dict(arrowstyle="->"))


runplot(df1, 'test1.csv', label='test1')
runplot(df2, 'test2.csv', label='test2')
runplot(df3, 'test3.csv', label='test3')
runplot(df4, 'test4.csv', label='test4')
runplot(df5, 'test5.csv', label='test5')

How can we make the legend show in the plots?

Answer 1

Set lebel argument when plot and use handle to make a legend. Try to write like this:

def runplot(df, title, label):   
    rows, cols = df.shape

    fig, ax = plt.subplots()
    line1, = ax.plot(df['price'].values, df['cost'].values, label=label)
    ax.legend(handles=[line1])

    plt.title(title)
    plt.annotate('test!', 
                 xy=(rows, df.ix[rows-1,'cost']),  
                 xycoords='data',
                 xytext=(-30,30),
                 textcoords='offset points',
                 arrowprops=dict(arrowstyle="->"))