An EBNF grammar based in the Lark Parser designed to parse multivariate date formats. (PT_BR)

dateparser_lark.py

#!/usr/bin/env python3
# coding: utf-8
#
#    Copyright © Neoway Business Solutions
#
#    @project: Diário Oficial
#     @author: Manoel Vilela
#

"""
An EBNF grammar based in the Lark Parser designed to
parse multivariate date formats. Grammar written for Portuguese in Mind.
"""

from lark import exceptions as LarkExceptions
from lark import Lark, InlineTransformer  # pip install lark-parser
from datetime import datetime


default_date_format = "%d/%m/%Y"
grammar = '''\
?date: day "de" month "de" year
     | day "/" month "/" year
     | day "-" month "-" year
     | day "." month "." year
     | day month year

day: INT
year: INT

month: month_name | month_number

month_name:
     | ("janeiro"   | "jan") -> jan
     | ("fevereiro" | "fev") -> fev
     | ("março"     | "mar") -> mar
     | ("abril"     | "abr") -> abr
     | ("maio"      | "mai") -> mai
     | ("junho"     | "jun") -> jun
     | ("julho"     | "jul") -> jul
     | ("agosto"    | "ago") -> ago
     | ("setembro"  | "set") -> set
     | ("outubro"   | "out") -> out
     | ("novembro"  | "nov") -> nov
     | ("dezembro"  | "dez") -> dez


month_number:
            | ["0"] "1" -> jan
            | ["0"] "2" -> fev
            | ["0"] "3" -> mar
            | ["0"] "4" -> abr
            | ["0"] "5" -> mai
            | ["0"] "6" -> jun
            | ["0"] "7" -> jul
            | ["0"] "8" -> ago
            | ["0"] "9" -> set
            | "10" -> out
            | "11" -> nov
            | "12" -> dez


%import common.WORD
%import common.INT
%import common.DIGIT
%import common.WS
%ignore WS
'''

month_dict = {
    "jan": 1,
    "fev": 2,
    "mar": 3,
    "abr": 4,
    "mai": 5,
    "jun": 6,
    "jul": 7,
    "ago": 8,
    "set": 9,
    "out": 10,
    "nov": 11,
    "dez": 12
}

parser = Lark(grammar, start='date')


class NaturalDateTree(InlineTransformer):
    day = int
    year = int

    def month(self, tree):
        month_label = tree._pretty_label()  # jan, fev
        return month_dict[month_label]

    def date(self, day, month, year):
        if year < 30:
            year += 2000
        elif year > 30 and year < 100:
            year += 1900

        try:
            return datetime(year, month, day)
        except ValueError:
            return None


def parse_date(expr):
    return NaturalDateTree().transform(parser.parse(expr))


def parse(date_string, date_format=default_date_format):
    try:
        parsed_date = parse_date(date_string.lower())
        if parsed_date is not None:
            return parsed_date.strftime(date_format)
    except LarkExceptions.UnexpectedCharacters:
        pass
    return None


def run_tests():
    tests = [
        ('02-08-2018', '02/08/2018'),
        ('1.03.2018', '01/03/2018'),
        ('1 de fevereiro de 2018', "01/02/2018"),
        ('02 fevereiro 2018', "02/02/2018"),
        ('28FEV2017', '28/02/2017'),
        ('31fev2019', None),
        ('shitty string', None),
        ('10 Mai 17', '10/05/2017'),
        ('08 Jun 98', '08/06/1998')
    ]

    for entry, expected in tests:
        parsed = parse(entry)
        assert parsed == expected, f"Expected: {expected!r}, but: {parsed!r}"


if __name__ == '__main__':
    run_tests()