python 等比数列

def is_geometric(li):  
    if len(li) <= 1:  
        return True  
    # Calculate ratio  
    ratio = li[1]/float(li[0])  
    # Check the ratio of the remaining  
    for i in range(1, len(li)):  
        if li[i]/float(li[i-1]) != ratio:   
            return False  
    return True   
  
print(is_geometric([2, 6, 18, 54]))  
  
print(is_geometric([10, 5, 2.5, 1.25]))  
  
print(is_geometric([5, 8, 9, 11]))