Go: package main

import "fmt"

func main() {
	var x1, x2, x3, y1, y2, y3, xp, yp float64
	for {
		v, _ := fmt.Scanf("%f %f %f %f %f %f %f %f", &x1, &y1, &x2, &y2, &x3, &y3, &xp, &yp)
		// println(x1, x2, x3, y1, y2, y3, xp, yp)
		if v != 8 {
			break
		}
		ok1 := true
		ok2 := true
		if (x2-x1)*(yp-y1)-(xp-x1)*(y2-y1)<0 {
			ok1 = false
		} else {
			ok2 = false
		}
		if (x3-x2)*(yp-y2)-(xp-x2)*(y3-y2)<0 {
			ok1 = false
		} else {
			ok2 = false
		}
		if (x1-x3)*(yp-y3)-(xp-x3)*(y1-y3)<0 {
			ok1 = false
		} else {
			ok2 = false
		}
		if ok1 || ok2 {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

Python: # -*- coding: utf-8 -*-
"""
http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0012&lang=jp

"""
import sys
from sys import stdin
input = stdin.readline



class Point(object):
    epsilon = 1e-10

    def __init__(self, x=0.0, y=0.0):
        if isinstance(x, tuple):
            self.x = x[0]
            self.y = x[1]
        else:
            self.x = x
            self.y = y

    # ????????????
    def __add__(self, other):
        return Point(self.x + other.x, self.y + other.y)

    def __sub__(self, other):
        return Point(self.x - other.x, self.y - other.y)

    def __mul__(self, other):
        return Point(other * self.x, other * self.y)

    def __truediv__(self, other):
        return Point(self.x / other, self.y / other)

    def __lt__(self, other):
        if self.x == other.x:
            return self.y < other.y
        else:
            return self.x < other.x

    def __eq__(self, other):
        from math import fabs
        if fabs(self.x - other.x) < Point.epsilon and fabs(self.y - other.y) < Point.epsilon:
            return True
        else:
            return False

    def norm(self):
        return self.x * self.x + self.y * self.y

    def __abs__(self):
        return sqrt(self.norm())

    def ccw(self, p0, p1):
        # ??????2???(p0, p1)?????????????????????????????????????????¢????????????
        a = Vector(p1 - p0)
        b = Vector(self - p0)
        if Vector.cross(a, b) > Point.epsilon:
            return 1 # 'COUNTER_CLOCKWISE'
        elif Vector.cross(a, b) < -Point.epsilon:
            return -1 # 'CLOCKWISE'
        elif Vector.dot(a, b) < -Point.epsilon:
            return 2 # 'ONLINE_BACK'
        elif a.norm() < b.norm():
            return -2 # 'ONLINE_FRONT'
        else:
            return 0 # 'ON_SEGMENT'

    def project(self, s):
        # ??????(Point)????????????s??????????????????????????????????????§?¨?(?°???±)????±???????
        base = Vector(s.p2 - s.p1)
        a = Vector(self - s.p1)
        r = Vector.dot(a, base)
        r /= base.norm()
        return s.p1 + base * r

    def reflect(self, s):
        # ??????s???????§°?????¨?????????????????¨???????§°??????????????§?¨?(????°?)????±???????
        proj = self.project(s)
        return self + (proj - self)*2

    def distance(self, s):
        # ????????¨??????s????????¢????¨??????????
        if Vector.dot(s.p2-s.p1, self-s.p1) < 0.0:
            return abs(self - s.p1)
        if Vector.dot(s.p1-s.p2, self-s.p2) < 0.0:
            return abs(self - s.p2)
        return abs(Vector.cross(s.p2-s.p1, self-s.p1) / abs(s.p2-s.p1))


class Vector(Point):
    def __init__(self, x=0.0, y=0.0):
        if isinstance(x, tuple):
            self.x = x[0]
            self.y = x[1]
        elif isinstance(x, Point):
            self.x = x.x
            self.y = x.y
        else:
            self.x = x
            self.y = y

    # ????????????
    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y)

    def __sub__(self, other):
        return Vector(self.x - other.x, self.y - other.y)

    def __mul__(self, other):
        return Vector(other * self.x, other * self.y)

    def __truediv__(self, other):
        return Vector(self.x / other, self.y / other)


    @classmethod
    def dot(cls, a, b):
        return a.x * b.x + a.y * b.y

    @classmethod
    def cross(cls, a, b):
        return a.x * b.y - a.y * b.x

    @classmethod
    def is_orthogonal(cls, a, b):
        return Vector.dot(a, b) == 0.0

    @classmethod
    def is_parallel(cls, a, b):
        return Vector.cross(a, b) == 0.0


class Segment(object):
    def __init__(self, p1=Point(), p2=Point()):
        if isinstance(p1, Point):
            self.p1 = p1
            self.p2 = p2
        elif isinstance(p1, tuple):
            self.p1 = Point(p1[0], p1[1])
            self.p2 = Point(p2[0], p2[1])

    def intersect(self, s):
        # ????????¨??????????????????????????????????????????????????????
        ans1 = s.p1.ccw(self.p1, self.p2) * s.p2.ccw(self.p1, self.p2)
        ans2 = self.p1.ccw(s.p1, s.p2) * self.p2.ccw(s.p1, s.p2)
        return ans1 <= 0 and ans2 <= 0

    def cross_point(self, s):
        # ????????¨??????????????????????????????????????§?¨?????±???????
        base = s.p2 - s.p1
        d1 = abs(Vector.cross(base, self.p1-s.p1))
        d2 = abs(Vector.cross(base, self.p2-s.p1))
        t = d1 / (d1 + d2)
        return self.p1 + (self.p2 - self.p1) * t

    def distance(self, s):
        # ????????¨?????????????????????????????¢????±???????
        if self.intersect(s):
            return 0.0
        d1 = s.p1.distance(self)
        d2 = s.p2.distance(self)
        d3 = self.p1.distance(s)
        d4 = self.p2.distance(s)
        return min(d1, d2, d3, d4)


    @classmethod
    def is_orthogonal(cls, s1, s2):
        a = Vector(s1.p2 - s1.p1)
        b = Vector(s2.p2 - s2.p1)
        return Vector.is_orthogonal(a, b)

    @classmethod
    def is_parallel(cls, s1, s2):
        a = Vector(s1.p2 - s1.p1)
        b = Vector(s2.p2 - s2.p1)
        return Vector.is_parallel(a, b)


class Line(Segment):
    pass


class Cirle(object):
    def __init__(self, x, y=Point(), r=1.0):
        if isinstance(x, Point):
            self.c = x
            self.r = y
        elif isinstance(x, tuple):
            self.c = Point(x[0], x[1])
            self.r = r

    def cross_points(self, s):
        if isinstance(s, Segment):
            pr = self.c.project(s)
            e = (s.p2 - s.p1) / abs(s.p2 - s.p1)
            base = sqrt(self.r * self.r - (pr - self.c).norm())
            return pr + e * base, pr - e * base
        elif isinstance(s, Cirle):
            c2 = s
            d = abs(self.c - c2.c)
            a = acos((self.r * self.r + d * d - c2.r * c2.r) / (2 * self.r * d))
            t = atan2(c2.c.y - self.c.y, c2.c.x - self.c.x)
            temp1 = Point(cos(t+a)*self.r, sin(t+a)*self.r)
            temp2 = Point(cos(t-a)*self.r, sin(t-a)*self.r)
            return self.c + temp1, self.c + temp2


def contains(polygon, p):
    n = len(polygon)
    x = False
    for i in range(n):
        a = polygon[i] - p
        b = polygon[(i+1)%n] - p
        if abs(Vector.cross(a, b)) < Point.epsilon and Vector.dot(a, b) < Point.epsilon:
            return 1
        if a.y > b.y:
            temp = a
            a = b
            b = temp
        if a.y < Point.epsilon and Point.epsilon < b.y and Vector.cross(a, b) > Point.epsilon:
            x = not x
    return 2 if x else 0


def main(args):
    for line in sys.stdin:
        polygon = []
        x1, y1, x2, y2, x3, y3, xp, yp = map(float, line.split())
        polygon.append(Point(x1, y1))
        polygon.append(Point(x2, y2))
        polygon.append(Point(x3, y3))
        result = contains(polygon, Point(xp, yp))
        if result == 2:
            print('YES')
        else:
            print('NO')


if __name__ == '__main__':
    main(sys.argv[1:])

Python: def isPos(p,x,y):
    return ((x-p).conjugate()*(y-p)).imag>0

try:
    while True:
        X=list(map(float,input().split()))
        a,b,c,p=map(lambda x:complex(*x),[X[:2],X[2:4],X[4:6],X[6:]])
        print(['NO','YES'][isPos(p,a,b)==isPos(p,b,c)==isPos(p,c,a)])
except EOFError: pass