2.7.1　拼接和格式化

字符串最常見的操作之一就是拼接。對于簡單的拼接，我們可以用“+”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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復雜一些的情況，我們還是可以通過“+”操作符來進行。

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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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更復雜一些的情況，我們仍然可以通過“+”操作符來完成，但是，這需要做大量碎片化的細節處理，很容易出錯，也不容易看出拼接字符串的最終全貌，這會帶來編碼、閱讀和維護方面的困難，我們需要更合適的方式來完成這類任務。

針對這種情況，我們可以用字符串的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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可以給括號占位符加上序號，進一步減少出錯的可能。

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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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甚至可以給占位符加上名字，這樣，可讀性和可維護性會進一步提高。

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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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通過占位符，format方法可以很靈活地處理字符串的格式化，同時還可以使代碼具有很高的可讀性和可維護性。