python 中列表和字符串能否相加 + append extend 对比

a = []
a += 'rff'
print(a)

a = []
a.extend( 'rff')
print(a)

a = []
a.append( 'rff')
print(a)
>>>>>>>>>>>result:
['r', 'f', 'f']
['r', 'f', 'f']
['rff']