如何在Python中分隔逗号分隔的字符串，除了引号内的逗号之外

Question

我想在Python中拆分逗号分隔的字符串。我这里棘手的部分是数据本身的一些字段中有一个逗号，它们用引号引起来（"或'）。生成的拆分字符串也应该在删除的字段周围加引号。另外，一些字段可以是空的。

例子：

hey,hello,,"hello,world",'hey,world' 

需要被分成5个部分，如下面

['hey', 'hello', '', 'hello,world', 'hey,world'] 

任何想法/想法/建议/着如何去解决在Python上述问题将有助于非常感激。

谢谢你， Vish

Answer 1

（编辑：原来的答案有麻烦的空字段t他边由于道路re.findall的作品，所以我重构了一点，并添加测试。）

import re 

def parse_fields(text): 
    r""" 
    >>> list(parse_fields('hey,hello,,"hello,world",\'hey,world\'')) 
    ['hey', 'hello', '', 'hello,world', 'hey,world'] 
    >>> list(parse_fields('hey,hello,,"hello,world",\'hey,world\',')) 
    ['hey', 'hello', '', 'hello,world', 'hey,world', ''] 
    >>> list(parse_fields(',hey,hello,,"hello,world",\'hey,world\',')) 
    ['', 'hey', 'hello', '', 'hello,world', 'hey,world', ''] 
    >>> list(parse_fields('')) 
    [''] 
    >>> list(parse_fields(',')) 
    ['', ''] 
    >>> list(parse_fields('testing,quotes not at "the" beginning \'of\' the,string')) 
    ['testing', 'quotes not at "the" beginning \'of\' the', 'string'] 
    >>> list(parse_fields('testing,"unterminated quotes')) 
    ['testing', '"unterminated quotes'] 
    """ 
    pos = 0 
    exp = re.compile(r"""(['"]?)(.*?)\1(,|$)""") 
    while True: 
     m = exp.search(text, pos) 
     result = m.group(2) 
     separator = m.group(3) 

     yield result 

     if not separator: 
      break 

     pos = m.end(0) 

if __name__ == "__main__": 
    import doctest 
    doctest.testmod() 

(['"]?)匹配一个可选的单或双引号。

(.*?)匹配字符串本身。这是一个非贪婪的比赛，可以根据需要进行匹配而不用吃整串。这被分配到result，这就是我们实际得到的结果。

\1是反向引用，以匹配我们之前匹配的相同单引号或双引号（如果有的话）。

(,|$)匹配逗号分隔每个条目或行尾。这被分配到separator。

如果分隔符是假的（例如空），那意味着没有分隔符，所以我们在字符串的末尾 - 我们完成了。否则，我们根据正则表达式的完成位置（m.end(0)）更新新的开始位置，然后继续循环。

Answer 2

听起来像是你想要的CSV模块。

Answer 3

csv模块不会同时处理“and”引号的情况，如果没有提供这种方言的模块，就必须进入解析业务。为了避免依赖第三方模块中，我们可以使用re模块进行词法分析，使用re.MatchObject.lastindex噱头将令牌类型与匹配的模式相关联

以下代码作为脚本运行时会通过所有显示的测试，与Python 2.7和2.2

import re 

# lexical token symbols 
DQUOTED, SQUOTED, UNQUOTED, COMMA, NEWLINE = xrange(5) 

_pattern_tuples = (
    (r'"[^"]*"', DQUOTED), 
    (r"'[^']*'", SQUOTED), 
    (r",", COMMA), 
    (r"$", NEWLINE), # matches end of string OR \n just before end of string 
    (r"[^,\n]+", UNQUOTED), # order in the above list is important 
    ) 
_matcher = re.compile(
    '(' + ')|('.join([i[0] for i in _pattern_tuples]) + ')', 
    ).match 
_toktype = [None] + [i[1] for i in _pattern_tuples] 
# need dummy at start because re.MatchObject.lastindex counts from 1 

def csv_split(text): 
    """Split a csv string into a list of fields. 
    Fields may be quoted with " or ' or be unquoted. 
    An unquoted string can contain both a " and a ', provided neither is at 
    the start of the string. 
    A trailing \n will be ignored if present. 
    """ 
    fields = [] 
    pos = 0 
    want_field = True 
    while 1: 
     m = _matcher(text, pos) 
     if not m: 
      raise ValueError("Problem at offset %d in %r" % (pos, text)) 
     ttype = _toktype[m.lastindex] 
     if want_field: 
      if ttype in (DQUOTED, SQUOTED): 
       fields.append(m.group(0)[1:-1]) 
       want_field = False 
      elif ttype == UNQUOTED: 
       fields.append(m.group(0)) 
       want_field = False 
      elif ttype == COMMA: 
       fields.append("") 
      else: 
       assert ttype == NEWLINE 
       fields.append("") 
       break 
     else: 
      if ttype == COMMA: 
       want_field = True 
      elif ttype == NEWLINE: 
       break 
      else: 
       print "*** Error dump ***", ttype, repr(m.group(0)), fields 
       raise ValueError("Missing comma at offset %d in %r" % (pos, text)) 
     pos = m.end(0) 
    return fields 

if __name__ == "__main__": 
    tests = (
     ("""hey,hello,,"hello,world",'hey,world'\n""", ['hey', 'hello', '', 'hello,world', 'hey,world']), 
     ("""\n""", ['']), 
     ("""""", ['']), 
     ("""a,b\n""", ['a', 'b']), 
     ("""a,b""", ['a', 'b']), 
     (""",,,\n""", ['', '', '', '']), 
     ("""a,contains both " and ',c""", ['a', 'contains both " and \'', 'c']), 
     ("""a,'"starts with "...',c""", ['a', '"starts with "...', 'c']), 
     ) 
    for text, expected in tests: 
     result = csv_split(text) 
     print 
     print repr(text) 
     print repr(result) 
     print repr(expected) 
     print result == expected 

Answer 4

我捏造了这样的东西。我猜想，这非常多余，但它为我做了这份工作。你必须有点适应它规范：

def csv_splitter(line): 
    splitthese = [0] 
    splitted = [] 
    splitpos = True 
    for nr, i in enumerate(line): 
     if i == "\"" and splitpos == True: 
      splitpos = False 
     elif i == "\"" and splitpos == False: 
      splitpos = True 
     if i == "," and splitpos == True: 
      splitthese.append(nr) 
    splitthese.append(len(line)+1) 
    for i in range(len(splitthese)-1): 
     splitted.append(re.sub("^,|\"","",line[splitthese[i]:splitthese[i+1]])) 
    return splitted