def _isLeft(a, b, c):
 return ((((b[0] - a[0]) * (c[1] - a[1])) - ((b[1] - a[1]) * (c[0] - a[0]))) > 0)

def _isLeft ( a , b , c ) : return ( ( ( ( b [ 0 ] - a [ 0 ] ) * ( c [ 1 ] - a [ 1 ] ) ) - ( ( b [ 1 ] - a [ 1 ] ) * ( c [ 0 ] - a [ 0 ] ) ) ) > 0 )
check if c is left of the infinite line from a to b .