from pylab import *
from numpy import *
def daylighthours(latitude,J):
    ds=0.4093*sin(2*pi/365*J-1.405)      # to be replaced by class 
    sha=arccos(-tan(latitude)*tan(ds))   # to be replaced by class 
    dh=24/pi*sha
    return dh
latitude=23
J=arange(1,365,1)
plot(J,daylighthours(latitude,J))
ytext = ylabel('daylight hours')
xtext = xlabel('Julian day')
show()