Question

我正在尝试在python中拆分逗号分隔的字符串。对我来说，棘手的部分是数据中的一些字段本身有一个逗号，它们用引号括起来（"或'）。生成的拆分字符串也应该删除字段周围的引号。此外，某些字段可能为空。

示例：

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

需要分为5个部分，如下所示

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

任何有关如何在Python中解决上述问题的想法/想法/建议/帮助都将非常感激。

谢谢你， Vish

Answer 1

听起来你想要CSV模块。

Answer 2

（编辑：由于re.findall的工作方式，原始答案在边缘上的空字段出现问题，所以我重构了一下并添加了测试。）

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()

(['"]?)匹配可选的单引号或双引号。

(.*?)匹配字符串本身。这是一个非贪婪的比赛，在不吃整个弦的情况下尽可能多地匹配。这被分配给result，这就是我们实际产生的结果。

\1是一个反向引用，用于匹配我们之前匹配的相同的单引号或双引号（如果有的话）。

(,|$)匹配分隔每个条目或行尾的逗号。这已分配给separator。

如果分隔符为假（例如为空），则表示没有分隔符，因此我们位于字符串的末尾 - 我们已完成。否则，我们根据正则表达式完成的位置（m.end(0)）更新新的起始位置，并继续循环。

Answer 3

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

以脚本形式运行时，以下代码将使用Python 2.7和2.2传递所有显示的测试。

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。我想这非常多余，但它确实适合我。你必须根据你的规格进行调整：

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

如何在Python中拆分逗号分隔的字符串，除了引号内的逗号

4 个答案: