how to color different times in matplotlib based on a classification condition, like when there was a recssion in python

main.py
import matplotlib.pyplot as plt
import pandas as pd

# Load some example GDP data
df = pd.read_csv('gdp_data.csv', index_col='date')

# Define a function to check if the GDP growth rate is negative
def is_recession(gdp_growth_rate):
    return gdp_growth_rate < 0

# Calculate the GDP growth rate
df['gdp_growth_rate'] = df['gdp'].pct_change() * 100

# Create a boolean Series indicating whether each point is in a recession or not
in_recession = df['gdp_growth_rate'].apply(is_recession)

# Create the plot
fig, ax = plt.subplots()
ax.plot(df.index, df['gdp'])

# Shade the regions where we were in a recession
ax.fill_between(df.index, 0, df['gdp'], where=in_recession, color='red', alpha=0.3)

# Add labels and title
ax.set_xlabel('Year')
ax.set_ylabel('GDP (trillions of dollars)')
ax.set_title('US GDP over time with recessions shaded')

plt.show()
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