python 正则表达式练习备忘录

感觉这正则表达式，还是要多实践，水平才能提高。

现在只是练习，知道其运用场合，掌握中心思想就差不多了。

附两个松散正则表达式样例：

>>> pattern = '''
    ^                   # beginning of string
    M{0,3}              # thousands - 0 to 3 Ms
    (CM|CD|D?C{0,3})    # hundreds - 900 (CM), 400 (CD), 0-300 (0 to 3 Cs),
                        #            or 500-800 (D, followed by 0 to 3 Cs)
    (XC|XL|L?X{0,3})    # tens - 90 (XC), 40 (XL), 0-30 (0 to 3 Xs),
                        #        or 50-80 (L, followed by 0 to 3 Xs)
    (IX|IV|V?I{0,3})    # ones - 9 (IX), 4 (IV), 0-3 (0 to 3 Is),
                        #        or 5-8 (V, followed by 0 to 3 Is)
    $                   # end of string
    '''
>>> re.search(pattern, 'M', re.VERBOSE)                 ①<_sre.SRE_Match object at 0x008EEB48>
>>> re.search(pattern, 'MCMLXXXIX', re.VERBOSE)         ②<_sre.SRE_Match object at 0x008EEB48>
>>> re.search(pattern, 'MMMDCCCLXXXVIII', re.VERBOSE)   ③<_sre.SRE_Match object at 0x008EEB48>
>>> re.search(pattern, 'M')                             ④

~~~~~~~~~~~~~~~~~~~~~~~~

>>> phonePattern = re.compile(r'''
                # don't match beginning of string, number can start anywhere
    (\d{3})     # area code is 3 digits (e.g. '800')
    \D*         # optional separator is any number of non-digits
    (\d{3})     # trunk is 3 digits (e.g. '555')
    \D*         # optional separator
    (\d{4})     # rest of number is 4 digits (e.g. '1212')
    \D*         # optional separator
    (\d*)       # extension is optional and can be any number of digits
    $           # end of string
    ''', re.VERBOSE)
>>> phonePattern.search('work 1-(800) 555.1212 #1234').groups()  ①('800', '555', '1212', '1234')
>>> phonePattern.search('800-555-1212')                          ②('800', '555', '1212', '')