A 2024 update: As of Scipy 1.15.2, Scipy has implemented a mixture distribution:

https://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.Mixture.html#scipy.stats.Mixture

import numpy as np
from scipy import stats
import matplotlib.pyplot as plt

mixture = stats.Mixture([stats.Normal(mu=1, sigma=5), stats.Normal(mu=2, sigma=1), stats.Normal(mu=-3, sigma=0.5)], weights=[0.2, 0.5, 0.3])

plt.rcParams['figure.figsize'] = (3,3)
pdf_xs = np.arange(-10, 10, 0.1)
plt.plot(pdf_xs, mixture.pdf(pdf_xs))
plt.title('PDF')