import matplotlib.pyplot as plt
import numpy as np
import scipy.stats as st
import arviz as az
plt.style.use('arviz-darkgrid')
x = np.arange(0, 15)
for m in [0.5, 3, 8]:
    pmf = st.poisson.pmf(x, m)
    plt.plot(x, pmf, '-o', label='$\mu$ = {}'.format(m))
plt.xlabel('x', fontsize=12)
plt.ylabel('f(x)', fontsize=12)
plt.ylim(0)
plt.legend(loc=1)
plt.show()