Python的string模組中的Template類字串模板用法

string.Template()
string.Template()內添加替換的字元, 使用"$"符號, 或 在字串內, 使用"${}"; 調用時使用string.substitute(dict)函數.
可以通過繼承"string.Template", 覆蓋變數delimiter(定界符)和idpattern(替換格式), 定製不同形式的模板.

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)必須包含底線, 所以第2個沒有進行替換.

正則替換

string.Template的pattern是一個Regex, 可以通過覆蓋pattern屬性, 定義新的Regex.
如: 使用新的定界符"{{", 把{{var}}作為變數文法.

代碼:

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')) 

輸出:

  \$(?:    (?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 

字串模板的安全替換(safe_substitute)
字串模板(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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