python3 标准库——string

String模块起源于Python最早的版本。以前在这模块实现的很多函数已经被转移到str对象方法中。string模块任然保留了几种有用的常量和类，本文主要来讨论它们。

Functions

函数capwords()将字符串中所有单词首字母大写。

In [1]: import string In [2]: s = 'The quick brown fox jumped over the lazy dog.' In [3]: print(s) The quick brown fox jumped over the lazy dog. In [4]: print(string.capwords(s)) The Quick Brown Fox Jumped Over The Lazy Dog.

结果相当于split(), 大写首字母然后join().

Templates

字符串格式化的几种用法：

In [5]: values = {'var': 'foo'} In [6]: t = string.Template(""" ...: Variable : $var ...: Escape : $$ ...: Variable in text: ${var}iable ...: """) In [7]: print('TEMPLATE:', t.substitute(values)) TEMPLATE: Variable : foo Escape : $ Variable in text: fooiable In [8]: s = """ ...: Variable : %(var)s ...: Escape : %% ...: Variable in text: %(var)siable ...: """ In [9]: print('INTERPOLATION:', s % values) INTERPOLATION: Variable : foo Escape : % Variable in text: fooiable In [10]: s = """ ...: Variable : {var} ...: Escape : {{}} ...: Variable in text: {var}iable ...: """ In [11]: print('FORMAT:', s.format(**values)) FORMAT: Variable : foo Escape : {} Variable in text: fooiable

对于string.Template,如果有字符串没有提供在参数里，应用safe_substitute():

In [12]: t = string.Template("$var is here but $missing is not provided") In [13]: try: ...: print('substitute() :', t.substitute(values)) ...: except KeyError as err: ...: print('ERROR:', str(err)) ...: ERROR: 'missing' In [14]: print('safe_substitute():', t.safe_substitute(values)) safe_substitute(): foo is here but $missing is not provided

由于没有与missing对应的值在字典中，substitute()函数引发KeyError, 而safe_substitute()捕捉到错误，把它依旧留在文本中。