unify_date.py

import arrow
from datetime import datetime


def unify_date(text: str):
    text = text.strip().lower()
    if text.startswith('circa'):
        text = text[len('circa') :].strip()
    try:
        return arrow.get(text).date()
    except arrow.parser.ParserError as e:
        # print('x', text)
        pass

    def gen_fmt():
        for sep in [' ', '-', '/']:
            for fmt in [
                ['%Y'],
                ['%b', '%Y'],
                ['%d', '%m', '%y'],
                ['%d', '%m', '%Y'],
                ['%d', '%b', '%Y'],
                ['%b', '%d', '%Y'],
            ]:
                yield sep.join(fmt)

    for fmt in gen_fmt():
        # print('f', fmt)
        try:
            return datetime.strptime(text, fmt).strftime('%Y-%m-%d')
        except ValueError:
            continue
    return text


data = [
    {"dob": "1975"},
    {"dob": "1965."},
    {"dob": "Oct 1960"},
    {"dob": "Sep 1938."},
    {"dob": "03/11/1957"},
    {"dob": "02 Aug 1984"},
    {"dob": "05 Jan 1967."},
    {"dob": "1975 to 1978."},
    {"dob": "circa 07 Jul 1966"},
    {"dob": "01 Jan 1979 to 31 Dec 1979"},
    {"dob": "26 Sep 1946 to 07 Dec 1946."},
]
for x in data:
    text = x['dob'].strip('. ').lower().split('to')[0].strip()
    print(unify_date(text))