Well, I know it's a little bit "long" for one line but it's still one line.

For given three points p1 = (x1,y1), p2 = (x2,y2), p3 = (x3,y3), we calculate the cross product of vector V1 = (p1 -> p2) and V2 = (p2 -> p3). If all cross products have same signs (all >= 0 or all <= 0), return True.

```
class Solution(object):
def isConvex(self, p):
"""
:type p: List[List[int]]
:rtype: bool
"""
return all(((p[i-1][0]-p[i][0])*(p[i][1]-p[i+1][1]) - \
(p[i][0]-p[i+1][0])*(p[i-1][1]-p[i][1])) >= 0 \
for i in range(-1, len(p)-1)) or \
all(((p[i-1][0]-p[i][0])*(p[i][1]-p[i+1][1]) - \
(p[i][0]-p[i+1][0])*(p[i-1][1]-p[i][1])) <= 0 \
for i in range(-1, len(p)-1))
```