Python中Template是string中的一个类，可以将字符串的格式固定下来，重复利用。
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
用法很简单，先生成一个模板实例s,然后调用替换函数substitute()将模板中的两个地方替换掉。替换的内容是通过字典对调用的，所以下面(lang='Python',howmany=3)出现的顺序可以不用严格的和模板中的一样。当然不用括号也是可以的。
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}时候，括号里的内容和括号要紧贴着，不然会报错。
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
当然在使用substitute()的时候，对应的关键字和值都要给出，不然会报错。
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()可以避免报错.
from string import Template
s = Template("there are ${howmany} ${lang} Quotation symbols")
print s.safe_substitute(lang='Python')
>>>there are ${howmany} Python Quotation symbols