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('$var') print(t.pattern.pattern) class mytemplate(string.template): delimiter = '{{' pattern = r''''' \{\{(?: (?p\{\{) | # escape sequence of two delimiters (?p[_a-z][_a-z0-9]*)\}\} | # delimiter and a python identifier {(?p[_a-z][_a-z0-9]*)}\}\} | # delimiter and a braced identifier (?p) # other ill-formed delimiter exprs ) ''' t2 = mytemplate(''''' {{{{ {{var}} ''') print('matches: ', t2.pattern.findall(t2.template)) print('substituted: ', t2.safe_substitute(var='replacement'))
输出:
\$(?: (?p\$) | # escape sequence of two delimiters (?p[_a-z][_a-z0-9]*) | # delimiter and a python identifier {(?p[_a-z][_a-z0-9]*)} | # delimiter and a braced identifier (?p) # other ill-formed delimiter exprs ) matches: [('{{', '', '', ''), ('', 'var', '', '')] substituted: {{ replacement
字符串模板的安全替换(safe_substitute)
字符串模板(sting.template), 替换时, 使用substitute(), 未能提供模板所需的全部参数值时, 会发生异常.
如果使用safe_substitute(), 即安全替换, 则会替换存在的字典值, 保留未存在的替换符号.
代码:
import string values = {'var' : 'foo'} t = string.template('''''$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!