import numpy as np
from scipy.stats import binom
import matplotlib.pyplot as plt
import math
import sys

n = float(sys.argv[1])  
p = float(sys.argv[2])

if len(sys.argv) > 3 :
    maxim = float(sys.argv[3])
else :
    maxim = n

fig, ax = plt.subplots(1, 1, figsize=(14,6.20))

minim = 0
rango = maxim-minim
ax.set_xlim(left=minim-rango/100, right=maxim+rango/100)
ax.xaxis.set_ticks(range(minim, int(maxim)+1, 5))

mean, var = binom.stats(n, p, moments='mv')
sigma = math.sqrt(var)
text="$n$ = %3d    $p$ = %3.2f          $\mu$ = %3.2f    $2\sigma$ = %3.2f" % (n,p,mean,2*sigma)
plt.xlabel(text)

x = np.arange(0,n+1)
ax.vlines(x, 0, binom.pmf(x, n, p), colors='b', lw=5, alpha=0.5)

y = np.array([mean-2*sigma,mean+2*sigma])
z = np.array([binom.pmf(int(n*p),n,p)/2,binom.pmf(int(n*p),n,p)/2])
ax.vlines(y, 0, z, colors='black', lw=2, linestyle = '--')

plt.show()