2.7.1　拼接和格式化

字符串最常见的操作之一就是拼接。对于简单的拼接，我们可以用“+”操作符很容易地做到。

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>>> name = 'world'
>>> greeting = 'Hello ' + name
>>> print(greeting)
Hello world

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复杂一些的情况，我们还是可以通过“+”操作符来进行。

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>>> pick_2002 = 'Yao Ming'
>>> pick_2003 = 'LeBron James'
>>> nba_draft_picks = 'First draft pick of NBA 2002 is ' + pick_2002 + ', and 
    the first draft pick of NBA 2003 is ' + pick_2003
>>> print(nba_draft_picks)
First draft pick of NBA 2002 is Yao Ming, and the first draft pick of NBA 2003 
    is LeBron James

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更复杂一些的情况，我们仍然可以通过“+”操作符来完成，但是，这需要做大量碎片化的细节处理，很容易出错，也不容易看出拼接字符串的最终全貌，这会带来编码、阅读和维护方面的困难，我们需要更合适的方式来完成这类任务。

针对这种情况，我们可以用字符串的format方法。

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>>> pick_2002 = 'Yao Ming'
>>> pick_2003 = 'LeBron James'
>>> 'First draft pick of 2002 is {}, and the first draft pick of 2003 is {}'.
    format(pick_2002, pick_2003)
'First draft pick of 2002 is Yao Ming, and the first draft pick of 2003 is 
    LeBron James'

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可以给括号占位符加上序号，进一步减少出错的可能。

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>>> pick_2002 = 'Yao Ming'
>>> pick_2003 = 'LeBron James'
>>> 'First draft pick of 2002 is {0}, and the first draft pick of 2003 is {1}'.
    format(pick_2002, pick_2003)
'First draft pick of 2002 is Yao Ming, and the first draft pick of 2003 is 
    LeBron James'

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甚至可以给占位符加上名字，这样，可读性和可维护性会进一步提高。

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>>> pick_2002 = 'Yao Ming'
>>> pick_2003 = 'LeBron James'
>>> 'First draft pick of 2002 is {pick_2002_name}, and the first draft pick of 
    2003 is {pick_2003_name}'.format(pick_2002_name=pick_2002, pick_2003_
    name=pick_2003)
'First draft pick of 2002 is Yao Ming, and the first draft pick of 2003 is 
    LeBron James'

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通过占位符，format方法可以很灵活地处理字符串的格式化，同时还可以使代码具有很高的可读性和可维护性。