组的Python正则表达式以匹配数量之前的文本

Question

I am trying to write a python regular expression which captures multiple values from a few columns in dataframe. Below regular expression attempts to do the same. There are 4 parts of the string.

group 1: Date - month and day
group 2: Date - month and day
group 3: description text before amount i.e. group 4
group 4: amount  - this group is optional

Some peculiar conditions for group 3 - text that (1)the text itself might contain characters like "-" , "$". So we cannot use - & $ as the boundary of text. (2) The text (group 3) sometimes may not be followed by amount. (3) Empty space between group 3 and 4 is optional

Below is python function code which takes in a dataframe having 4 columns c1,c2,c3,c4 adds the columns dt, txt and amt after processing to dataframe.

def parse_values(args):
    re_1='(([JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC]{3}\s{0,}[\d]{1,2})\s{0,}){2}(.*[\s]|.*[^\$]|.*[^-]){1}([-+]?\$[\d|,]+(?:\.\d+)?)?'
    srch=re.search(re_1, args[0])
    if srch is None:
        return args
    m = re.match(re_1, args[0])
    args['dt']=m.group(1)
    args['txt']=m.group(3)
    args['amt']=m.group(4)
    if m.group(4) is None:
        if pd.isnull(args['c3']):
            args['amt']=args.c2
        else:
            args['amt']=args.c3
    return args

And in order to test the results I have below 6 rows which needs to return a properly formatted amt column in return.

tt=[{'c1':'OCT 7 OCT 8 HURRY CURRY THORNHILL ','c2':'$16.84'},
        {'c1':'OCT 7 OCT 8 HURRY CURRY THORNHILL','c2':'$16.84'},
        {'c1':'MAR 15 MAR 16 LOBLAWS FOODS INC - EAST YORK -$80,00,7770.70'},
        {'c1':'MAR 15 MAR 16 LOBLAWS FOODS INC - EAST YORK-$2070.70'},
        {'c1':'MAR 15 MAR 16 LOBLAWS FOODS INC - EAST YORK$2070.70'},
        {'c1':'MAR 15 MAR 16 LOBLAWS FOODS INC - EAST YORK $80,00,7770.70'}
    ]
t=pd.DataFrame(tt,columns=['c1','c2','c3','c4'])
t=t.apply(parse_values,1)
t

However due to the error in my regular expression in re_1 I am not getting the amt column and txt column parsed properly as they return NaN or miss some words (as dipicted in some rows of the output image below).

Answer 1

How about this:

(((?:JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)\s*[\d]{1,2})\s*){2}(.*?)\s*(?=[\-$])([-+]?\$[\d|,]+(?:\.\d+)?)

As seen at regex101.com

Explanation:

First off, I've shortened the regex by changing a few minor details like using \\s* instead of \\s{0,} , which mean the exact same thing.

The whole [Jan|...|DEC] code was using a character class ie [] , whcih only takes a single character from the entire set. Using non capturing groups is the correct way of selecting from different groups of multiple letters, which in your case are 'months'.

The meat of the regex: LOOKAHEADS

(?=[\\-$]) tells the regex that the text before it in (.*) should match as much as it can until it finds a position followed by a dash or a dollar sign. Lookaheads don't actually match whatever they're looking for, they just tell the regex that the lookahead's arguments should be following that position.