Python-String:Template
Template python string提供的一个字符串模板，要用于文本处理
from string import template
两种substitute方法
1.substitute
# key必须被替代字符串配对，否则抛出ValueError
lan = Template('$python is $best')
lan.substitute(python = "C++",best ="also best")
'C++ is also best'
2.safe_substitute
# 不抛出任何异常，能配对的配对，不能的保留
lan.safe_substitute(python = "C++")
'C++ is $best'
lan.safe_substitute()
'$python is $best'
lan.safe_substitute(best="also best")
'$python is also best'
substitute（mapping ，**kwds）
lan = Template('$python is $best')
d = dict(python='time')
lan.safe_substitute(d)
'time is $best'
同时接受mapping and **kwd ，kwds优先
test_s = Template('$python is $best')
d=dict(python = 'favourite')
test_s.safe_substitute(d,python="aka")
'aka is $best'
