Extracting multiple date formats through regex in python

Question

I am trying to extract date from text in python. These are the possible texts and date patterns in it.

"Auction details: 14 December 2016, Pukekohe Park"
"Auction details: 17 Feb 2017, Gold Sacs Road"
"Auction details: Wednesday 27 Apr 1:00 p.m. (On site)(2016)"
"Auction details: Wednesday 27 Apr 1:00 p.m. (In Rooms - 923 Whangaa Rd, Man)(2016)"
"Auction details: Wed 27 Apr 2:00 p.m., 48 Viaduct Harbour Ave, Auckland, (2016)"
"Auction details: November 16 Wednesday 2:00pm at 48 Viaduct Harbour Ave, Auckland(2016)"
"Auction details: Thursday, 28th February '19"
"Auction details: Friday, 1st February '19"

This is what I have written so far,

mon = ' (?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(Nov|Dec)(?:ember)?) '
day1 = r'\d{1,2}'
day_test = r'\d{1,2}(?:th)|\d{1,2}(?:st)' 
year1 = r'\d{4}'
year2 = r'\(\d{4}\)'
dummy = r'.*'

This captures cases 1,2.

match = re.search(day1 + mon + year1, "Auction details: 14 December 2016, Pukekohe Park")
print match.group()

This somewhat captures case 3,4,5. But it prints everything from the text, so in the below case, I want 25 Nov 2016, but the below regex pattern gives me 25 Nov 3:00 p.m. (On Site)(2016).

So Question 1 : How to get only the date here?

match = re.search(day1 + mon + dummy + year2, "Friday 25 Nov 3:00 p.m. (On Site)(2016)")
print match.group()

Question 2 : Similarly, how do capture case 6,7 and 8 ?? What is the regex should be for that?

If not, is there any other better way to capture date from these formats?

Yes. It always starts with auction details. But not sure how sorting helps here. It will be great if you can explain. — ds_user
– ds_user, Commented Mar 6, 2019 at 7:28
Thanks. But it is not picking year in brackets. For cases 3,4,5,6. — ds_user
– ds_user, Commented Mar 6, 2019 at 7:30
I am happy to have multiple regex to handle this, it doesn't need to be one big regex. I can do if else loop to get it. As long as we cover all the scenarios. — ds_user
– ds_user, Commented Mar 6, 2019 at 7:31

Wiktor Stribiżew · Accepted Answer · 2019-03-06 07:58:42Z

You may try

((?:(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(?:Nov|Dec)(?:ember)?)\s+\d{1,2}(?:st|nd|rd|th)?|\d{1,2}(?:st|nd|rd|th)?\s+(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(?:Nov|Dec)(?:ember)?)))(?:.*(\b\d{2}(?:\d{2})?\b))?

See the regex demo.

Note I made all groups in the regex blocks non-capturing ((Nov|Dec) -> (?:Nov|Dec)), added (?:st|nd|rd|th)? optional group after day digit pattern, changed the year matching pattern to \b\d{2}(?:\d{2})?\b so that it only match 4- or 2-digit chunks as whole words, and created an alternation group to account for dates where day comes before month and vice versa.

The day and month are captured into Group 1 and the year is captured into Group 2, so the result is the concatenation of both.

NOTE: In case you need to match years in a safer way you may want to precise the year pattern. E.g., if you want to avoid matching the 4- or 2-digit whole words after :, add a negative lookbehind:

year1 = r'\b(?<!:)\d{2}(?:\d{2})?\b'
            ^^^^^^

Also, you may add word boundaries around the whole pattern to ensure a whole word match.

Here is the Python demo:

import re
mon = r'(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(?:Nov|Dec)(?:ember)?)'
day1 = r'\d{1,2}(?:st|nd|rd|th)?'
year1 = r'\b\d{2}(?:\d{2})?\b'
dummy = r'.*'

rx = r"((?:{smon}\s+{sday1}|{sday1}\s+{smon}))(?:{sdummy}({syear1}))?".format(smon=mon, sday1=day1, sdummy=dummy, syear1=year1)
# Or, try this if a partial number before a date is parsed as day:
# rx = r"\b((?:{smon}\s+{sday1}|{sday1}\s+{smon}))(?:{sdummy}({syear1}))?".format(smon=mon, sday1=day1, sdummy=dummy, syear1=year1)
strs = ["Auction details: 14 December 2016, Pukekohe Park","Auction details: 17 Feb 2017, Gold Sacs Road","Auction details: Wednesday 27 Apr 1:00 p.m. (On site)(2016)","Auction details: Wednesday 27 Apr 1:00 p.m. (In Rooms - 923 Whangaa Rd, Man)(2016)","Auction details: Wed 27 Apr 2:00 p.m., 48 Viaduct Harbour Ave, Auckland, (2016)","Auction details: November 16 Wednesday 2:00pm at 48 Viaduct Harbour Ave, Auckland(2016)","Auction details: Thursday, 28th February '19","Auction details: Friday, 1st February '19","Friday 25 Nov 3:00 p.m. (On Site)(2016)"]  
for s in strs:
    print(s)
    m = re.search(rx, s)
    if m:
        print("{} {}".format(m.group(1), m.group(2)))
    else:
        print("NO MATCH")

Output:

Auction details: 14 December 2016, Pukekohe Park
14 December 2016
Auction details: 17 Feb 2017, Gold Sacs Road
17 Feb 2017
Auction details: Wednesday 27 Apr 1:00 p.m. (On site)(2016)
27 Apr 2016
Auction details: Wednesday 27 Apr 1:00 p.m. (In Rooms - 923 Whangaa Rd, Man)(2016)
27 Apr 2016
Auction details: Wed 27 Apr 2:00 p.m., 48 Viaduct Harbour Ave, Auckland, (2016)
27 Apr 2016
Auction details: November 16 Wednesday 2:00pm at 48 Viaduct Harbour Ave, Auckland(2016)
November 16 2016
Auction details: Thursday, 28th February '19
28th February 19
Auction details: Friday, 1st February '19
1st February 19
Friday 25 Nov 3:00 p.m. (On Site)(2016)
25 Nov 2016

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