菜鸡求教，为什么从切片删除数目不对

书上习题写完了没事儿写着玩，问题在第 13 行开始，我想把 C = red 的都删除掉
为什么我的运行结果只剩下了一个？

alines = []
for alines_No in range (5):
new_aline = {"C":"red","Point":"10","Speed":"5"}
alines.append(new_aline)

for aline in alines:
print (aline)
print (len(alines))

for aline in alines[:2]:
if aline['C'] == 'red':
del alines[:2]
print (alines)


run

{'C': 'red', 'Point': '10', 'Speed': '5'}
{'C': 'red', 'Point': '10', 'Speed': '5'}
{'C': 'red', 'Point': '10', 'Speed': '5'}
{'C': 'red', 'Point': '10', 'Speed': '5'}
{'C': 'red', 'Point': '10', 'Speed': '5'}
5
[{'C': 'red', 'Point': '10', 'Speed': '5'}]
[Finished in 0.1s]