How can I fix the histogram

You make barsit but don't use it. Everything works fine if the binsoption is set histtobars

bars= [0,1,2,3,4,5,6,7,8,9]
hist(nums,bins=bars)

To set yticksto only integer values, you can use the slave module:MultipleLocatormatplotlib.ticker

from numpy import *
from matplotlib.pyplot import*
import matplotlib.ticker as ticker
from random import*

nums = []
N = 10
for i in range(N):
    a = randint(0,10)
    nums.append(a)

bars= [0,1,2,3,4,5,6,7,8,9]
hist(nums,bins=bars)

gca().yaxis.set_major_locator(ticker.MultipleLocator(1))

show()