Python中Template使用的一個小技巧

Python中Template是string中的一個類，可以將字符串的格式固定下來，重復利用。

from string import Template
s = Template("there are ${howmany} ${lang} Quotation symbols")
print s.substitute(lang='Python',howmany=3)
>>>there are 3  Python Quotation symbols

用法很簡單，先生成一個模板實例s,然后調用替換函數substitute()將模板中的兩個地方替換掉。替換的內容是通過字典對調用的，所以下面(lang='Python',howmany=3)出現的順序可以不用嚴格的和模板中的一樣。當然不用括號也是可以的。

from string import Template
s = Template("there are $howmany $lang Quotation symbols")
print s.substitute(lang='Python',howmany=3)
>>>there are 3  Python Quotation symbols

注意：在使用${howmany} ${lang}時候，括號里的內容和括號要緊貼着，不然會報錯。

from string import Template
s = Template("there are ${ howmany } ${lang} Quotation symbols")
print s.substitute(lang='Python',howmany=3)
>>>Traceback (most recent call last):
  File "E:/�������/201703/DeepLearning/neural-networks-and-deep-learning-master/src/validation.py", line 39, in <module>
    print s.substitute(lang='Python',howmany=3)
  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 176, in substitute
    return self.pattern.sub(convert, self.template)
  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 173, in convert
    self._invalid(mo)
  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 146, in _invalid
    (lineno, colno))
ValueError: Invalid placeholder in string: line 1, col 11

當然在使用substitute()的時候，對應的關鍵字和值都要給出，不然會報錯。

from string import Template
s = Template("there are ${ howmany } ${lang} Quotation symbols")
print s.substitute(lang='Python')
>>>Traceback (most recent call last):
  File "E:/�������/201703/DeepLearning/neural-networks-and-deep-learning-master/src/validation.py", line 39, in <module>
    print s.substitute(lang='Python')
  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 176, in substitute
    return self.pattern.sub(convert, self.template)
  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 166, in convert
    val = mapping[named]
KeyError: 'howmany'

使用safe_substitute()可以避免報錯.

from string import Template
s = Template("there are ${howmany} ${lang} Quotation symbols")
print s.safe_substitute(lang='Python')
>>>there are ${howmany} Python Quotation symbols