Python的string模块中的Template类字符串模板用法


            string.Template()

string.Template()内添加替换的字符, 使用"$"符号, 或 在字符串内, 使用"${}"; 调用时使用string.substitute(dict)函数.

可以通过继承"string.Template", 覆盖变量delimiter(定界符)和idpattern(替换格式), 定制不同形式的模板.

代码:





# -*- coding: utf-8 -*- 



import string 

 

template_text = ''''' 

  Delimiter : %% 

  Replaced : %with_underscore 

  Ingored : %notunderscored 

''' 

 

d = {'with_underscore' : 'replaced', 

   'notunderscored' : 'not replaced'} 

 

class MyTemplate(string.Template): 

  delimiter = '%' 

  idpattern = '[a-z]+_[a-z]+' 

   

t = MyTemplate(template_text) 

print('Modified ID pattern: ') 

print(t.safe_substitute(d)) 







输出:





Modified ID pattern:  

 

  Delimiter : % 

  Replaced : replaced 

  Ingored : %notunderscored 







注意: 定界符(delimiter)为"%", 替换模式(idpattern)必须包含下划线, 所以第2个没有进行替换.

正则替换

string.Template的pattern是一个正则表达式, 可以通过覆盖pattern属性, 定义新的正则表达式.

如: 使用新的定界符"{{", 把{{var}}作为变量语法.

代码:





import string 

 

t = string.Template('$var') 

print(t.pattern.pattern) 

 

class MyTemplate(string.Template): 

  delimiter = '{{' 

  pattern = r''''' 

  \{\{(?: 

   (?P<escaped>\{\{) |  # Escape sequence of two delimiters 

   (?P<named>[_a-z][_a-z0-9]*)\}\}   |  # delimiter and a Python identifier 

   {(?P<braced>[_a-z][_a-z0-9]*)}\}\}  |  # delimiter and a braced identifier 

   (?P<invalid>)       # Other ill-formed delimiter exprs 

  ) 

  ''' 

   

t2 = MyTemplate(''''' 

{{{{ 

{{var}} 

''') 

 

print('MATCHES: ', t2.pattern.findall(t2.template)) 

print('SUBSTITUTED: ', t2.safe_substitute(var='replacement')) 







输出:







  \$(?: 

   (?P<escaped>\$) |  # Escape sequence of two delimiters 

   (?P<named>[_a-z][_a-z0-9]*)   |  # delimiter and a Python identifier 

   {(?P<braced>[_a-z][_a-z0-9]*)}  |  # delimiter and a braced identifier 

   (?P<invalid>)       # Other ill-formed delimiter exprs 

  ) 

   

MATCHES: [('{{', '', '', ''), ('', 'var', '', '')] 

SUBSTITUTED:  

{{ 

replacement 





字符串模板的安全替换(safe_substitute) 

字符串模板(sting.Template), 替换时, 使用substitute(), 未能提供模板所需的全部参数值时, 会发生异常.

如果使用safe_substitute(), 即安全替换, 则会替换存在的字典值, 保留未存在的替换符号.

代码:







import string 

 

values = {'var' : 'foo'} 

 

t = string.Template('''''$var is here but $ missing is not provided! ''') 

 

 

try: 

  print 'substitute() : ', t.substitute(values) 

except ValueError as err: 

  print 'Error:', str(err) 

   

print 'safe_substitude() : ', t.safe_substitute(values) 





输出:





substitute() : Error: Invalid placeholder in string: line 1, col 18 

safe_substitude() : foo is here but $ missing is not provided!