Python正则表达式找不到匹配项

Question

I have the following file which I am trying to extract the date from 20131013.csv

Using the regex (?P<yyyy>\\\\d{4})(?P<mm>\\\\d{2})(?P<dd>\\\\d{2})

def getEffectiveDate(regex, fileName) :
    parts = 'yyyy-mm-dd'
    formatString = '%s-%s-%s 00:00:00'
    regexGroups = parts.split("-")
    m = re.search(regex, fileName)
    if m :
        vals = []
        for regexGroup in regexGroups :
            vals.append(m.group(regexGroup))
        value = formatString%tuple(vals)
    return value

when I pass in getEffectiveDate('(?P<yyyy>\\\\d{4})(?P<mm>\\\\d{2})(?P<dd>\\\\d{2})', '20131013.csv') I don't find any matches.

However the regex (?P<yyyy>\\\\d{4})-(?P<mm>\\\\d{2})-(?P<dd>\\\\d{2}) will find a match on 2013-10-13.csv

I am wondering if this is being caused by there being nothing inbetween the regex groups and if there is anything I can do to fix this?

EDIT:

I found a solution by doing regex.replace('\\\\\\\\', '\\\\')

The double backslashes were causing an issue with matching. I had only tried the regex (?P<yyyy>\\\\d{4})-(?P<mm>\\\\d{2})-(?P<dd>\\\\d{2}) as a raw string so it was working in that case.

Answer 1

Your code works for me. And it's better to define the regex as raw string.

>>> re.search(r'(?P<yyyy>\d{4})(?P<mm>\d{2})(?P<dd>\d{2})', '20131013.csv')
<_sre.SRE_Match object; span=(0, 8), match='20131013'>
>>> re.search(r'(?P<yyyy>\d{4})(?P<mm>\d{2})(?P<dd>\d{2})', '20131013.csv').group(1)
'2013'
>>> re.search(r'(?P<yyyy>\d{4})(?P<mm>\d{2})(?P<dd>\d{2})', '20131013.csv').group(2)
'10'
>>> re.search(r'(?P<yyyy>\d{4})(?P<mm>\d{2})(?P<dd>\d{2})', '20131013.csv').group(3)
'13'