a = 'python' ， a为True。print('hello,', a or 'world') 或计算中字串符结果是False，所以显示结果为a=‘python’。b = ''，b是空值，print('hello,', b or 'world')，或计算中不显示空值，是以结果显示为world。
>>> template='Life is short,you need {}'
>>> a='Python'
>>> result=template.format(a)
>>> print(result)
Life is short,you need Python
或者
>>> template='Life is short,{}'
>>> a='you need Python'
>>> result=template.format(a)
>>> print(result)
Life is short,you need Python
