Check if point is inside triangle

check.py

import matplotlib.pyplot as lpt
import numpy as np

def pt(data, point=None):
    p = plt.Polygon(data, closed=True, fill=None)
    ax = plt.gca()
    ax.add_patch(p)
    x=data[:,0]
    y=data[:,1]
    if point:
        x=x
        y=y
    ax.set_xlim(x.min()-1,x.max()+1)
    ax.set_ylim(y.min()-1,y.max()+1)
    
    if point:
        plt.plot(point[0], point[1], 'xr', markersize=20)


def cross(a,b):
    '#cross product of two 2d vectors'
    return a[0]*b[1] - a[1]*b[0]

def inside(p, t):
    'Is point p inside triangle y'
    def test(a,b,c):
        '''test if cross product BA x PA  and BA x BC has same sign, 
        this mean that P is on same side as C - towards the triangle inside '''
        u=cross(t[b]-t[a], p-t[a])
        v=cross(t[b]-t[a], t[c]-t[a])
        return u*v >= 0   # if 0 then P is BA line
    
    # for point to be inside triagle it must lay inside relative to all three sides
    return test(0,1,2) and test(1,2,0) and test(2,0, 1)

test.py

t=np.array([[0,0], [10,0], [5,10]])
p=[5,5]
pt(t, p)
print 'P is inside', inside(p,t)
p2=[10,4]
plt.plot(p2[0], p2[1], 'og')
print 'P2 is inside', inside(p2,t)