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!