Python之string模块的使用

string模块作用

string模块在最早的Python版本中就已经有了。以前这个模块中提供的很多函数已移值为str对象的方法，不过这个模块仍保留了很多有用的常量和类的处理str对象。

1、把字符串所有单词首字母变成大写

import string

s = 'The quick brown fox jumped over the lazy dog.'

print(s)
print(string.capwords(s))

运行效果

The quick brown fox jumped over the lazy dog.
The Quick Brown Fox Jumped Over The Lazy Dog.

2、字符串模板格式化

import string

values = {'var': 'foo'}

t = string.Template("""
Variable        : $var 
Escape          : $$  
Variable in text: ${var}iable 
""")
# ${var} #获取字典的值
# $var  #获取字典的键
print('TEMPLATE:', t.substitute(values))

s = """
Variable        : %(var)s
Escape          : %%
Variable in text: %(var)siable
"""

print('INTERPOLATION:', s % values)

s = """
Variable        : {var}
Escape          : {{}}
Variable in text: {var}iable
"""

print('FORMAT:', s.format(**values))

运行效果

TEMPLATE: 
Variable        : foo 
Escape          : $  
Variable in text: fooiable 

INTERPOLATION: 
Variable        : foo
Escape          : %
Variable in text: fooiable

FORMAT: 
Variable        : foo
Escape          : {}
Variable in text: fooiable

3、模板变量值没有设置时，异常的处理

import string

values = {'var': 'foo'}

t = string.Template("$var is here but $missing is not provided")

try:
    print('substitute()     :', t.substitute(values))
except KeyError as err:
    print('ERROR:', str(err))

print('safe_substitute():', t.safe_substitute(values))

运行效果

ERROR: 'missing'
safe_substitute(): foo is here but $missing is not provided

4、高级模板，指定限定符和匹配正则表达式，进行字符串模板替换

import string


class MyTemplate(string.Template):
    delimiter = '%'
    idpattern = '[a-z]+_[a-z]+'


template_text = '''
  Delimiter : %%
  Replaced  : %with_underscore
  Ignored   : %notunderscored
'''

d = {
    'with_underscore': 'replaced',
    'notunderscored': 'not replaced',
}

t = MyTemplate(template_text)
print('Modified ID pattern:')
print(t.safe_substitute(d))

 运行效果

Modified ID pattern:

  Delimiter : %
  Replaced  : replaced
  Ignored   : %notunderscored

5、打印出4个命名组，分别捕获转义定界符、命名变量、加括号的变量名和不合法的定界符模式。

import string

t = string.Template('$var')
print(t.pattern.pattern)

运行效果

    \$(?:
      (?P<escaped>\$) |   # Escape sequence of two delimiters
      (?P<named>(?a:[_a-z][_a-z0-9]*))      |   # delimiter and a Python identifier
      {(?P<braced>(?a:[_a-z][_a-z0-9]*))}  |   # delimiter and a braced identifier
      (?P<invalid>)              # Other ill-formed delimiter exprs
    )

6、自定义正式表达式，匹配字符和替换字符的示例

import string


class MyTemplate(string.Template):
    delimiter = '{{'
    pattern = r'''
    \{\{(?:
    (?P<escaped>\{\{)|
    (?P<named>[_a-z][_a-z0-9]*)\}\}|
    (?P<braced>[_a-z][_a-z0-9]*)\}\}|
    (?P<invalid>)
    )
    '''


t = MyTemplate('''
{{{{
{{var}}
''')

print('MATCHES:', t.pattern.findall(t.template))
print('SUBSTITUTED:', t.safe_substitute(var='replacement'))

运行效果

MATCHES: [('{{', '', '', ''), ('', 'var', '', '')]
SUBSTITUTED: 
{{
replacement

7、string模块包含大量的常量值，如果开发过程中有需要的时候，可以获取出来

import inspect
import string


def is_str(value):
    return isinstance(value, str)


for name, value in inspect.getmembers(string, is_str):
    if name.startswith('_'):
        continue
    print('%s=%r\n' % (name, value))

 

运行效果

ascii_letters='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

ascii_lowercase='abcdefghijklmnopqrstuvwxyz'

ascii_uppercase='ABCDEFGHIJKLMNOPQRSTUVWXYZ'

digits='0123456789'

hexdigits='0123456789abcdefABCDEF'

octdigits='01234567'

printable='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c'

punctuation='!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'

whitespace=' \t\n\r\x0b\x0c'