string.Template()
string.Template()內添加替換的字符, 使用"$"符號, 或 在字符串內, 使用"${}"; 調用時使用string.substitute(dict)函數.
可以通過繼承"string.Template", 覆蓋變量delimiter(定界符)和idpattern(替換格式), 定制不同形式的模板.
代碼:
# -*- 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)) 輸出:
Modified ID pattern: Delimiter : % Replaced : replaced Ingored : %notunderscored
注意: 定界符(delimiter)為"%", 替換模式(idpattern)必須包含下劃線, 所以第2個沒有進行替換.
正則替換
string.Template的pattern是一個正則表達式, 可以通過覆蓋pattern屬性, 定義新的正則表達式.
如: 使用新的定界符"{{", 把{{var}}作為變量語法.
代碼:
import string t = string.Template('$var') print(t.pattern.pattern) class MyTemplate(string.Template): delimiter = '{{' pattern = r''''' /{/{(?: (?P<escaped>/{/{) | # Escape sequence of two delimiters (?P<named>[_a-z][_a-z0-9]*)/}/} | # delimiter and a Python identifier {(?P<braced>[_a-z][_a-z0-9]*)}/}/} | # delimiter and a braced identifier (?P<invalid>) # Other ill-formed delimiter exprs ) ''' t2 = MyTemplate(''''' {{{{ {{var}} ''') print('MATCHES: ', t2.pattern.findall(t2.template)) print('SUBSTITUTED: ', t2.safe_substitute(var='replacement')) 輸出:
/$(?: (?P<escaped>/$) | # Escape sequence of two delimiters (?P<named>[_a-z][_a-z0-9]*) | # delimiter and a Python identifier {(?P<braced>[_a-z][_a-z0-9]*)} | # delimiter and a braced identifier (?P<invalid>) # Other ill-formed delimiter exprs ) MATCHES: [('{{', '', '', ''), ('', 'var', '', '')] SUBSTITUTED: {{ replacement 字符串模板的安全替換(safe_substitute)
字符串模板(sting.Template), 替換時, 使用substitute(), 未能提供模板所需的全部參數值時, 會發生異常.
如果使用safe_substitute(), 即安全替換, 則會替換存在的字典值, 保留未存在的替換符號.
代碼:
import string values = {'var' : 'foo'} t = string.Template('''''$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) 輸出:
substitute() : Error: Invalid placeholder in string: line 1, col 18 safe_substitude() : foo is here but $ missing is not provided!
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