readfile.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# vim: tabstop=4 shiftwidth=4 expandtab

import sys, os, re
from time import strptime

__title__ = "readfile"
__version__ = "0.1"

def read_file_lines(filename):
    if not os.path.isfile(filename):
        print('Input file does not exist. Try it again')
        exit(1)
    else:
        with open(filename) as f:
            file_content = f.read().splitlines()
    return file_content


def is_positive_integer(string):
    try:
        number = int(string)
        if number > 0:
            return True
        else:
            return False
    except ValueError:
        print("ID is not an integer. Line discarded.")
        return False


def process_strings(strings):
    parsed_strings = []
    while strings != "":
        strings = strings.lstrip()
        if re.match(r'^\\?".*$', strings):
            split = re.search(r'(^\\?".*?\\?") +(.*)?', strings)
            if split is not None:
                parsed_strings.append(split.group(1))
                if split.group(2) is not None:
                    strings = split.group(2)
                else:
                    break
            else:
                parsed_strings.append(strings)
                break
        else:
            split = strings.split(' ', 1)
            parsed_strings.append(split[0])
            if len(split) > 1: strings = split[1]
            else: break

    return parsed_strings


def user_input_and_result(dictionary, invalid_lines):
    print('Please provide a comma separated list of ids to show string2')
    ids = input()

    if re.match('^[0-9]+(,[0-9]+)*', ids):
        for num in ids.split(','):
            if num in dictionary:
                for string in dictionary[num]:
                    print(num + " " + string)
            else:
                print('Id: ' + num + ', does not exist in the input file')
    else:
        print('Input you provided is not a comma separated list of positive integers.')

    print("Invalid lines: " + str(invalid_lines))


def main():
    try:
        filename = sys.argv[1]
    except IndexError:
        print('Input file to read from, not provided. Please try it again.')
        exit(1)

    file_content = read_file_lines(filename)

    invalid_lines = 0
    db = {}
    for line in file_content:
        line_array = line.split(' ', 1)

        # Get the Id of the line and validate is positive integer
        line_id = line_array[0]

        if not is_positive_integer(line_id):
            invalid_lines += 1
            continue

        line_array = line_array[1].lstrip().split(' ', 1)

        # Line must have at least: ID, Datetime and Strings
        if len(line_array) < 2:
            invalid_lines += 1
            continue

        # Validate that the second string is in the format date-time
        try:
            strptime(line_array[0],'%Y-%m-%d-%H:%M:%S')
        except ValueError:
            invalid_lines += 1
            continue

        # Now that we checked the id and the date-time it's time to
        # evaluate the strings.
        strings = process_strings(line_array[1])

        # Validates that the row has at least 3 strings after the Id and the
        # date-time
        if len(strings) < 3:
            invalid_lines += 1
            continue

        if line_id in db:
            db[line_id].append(strings[1])
        else:
            db[line_id] = [strings[1]]

    user_input_and_result(db, invalid_lines)


if __name__ == '__main__':
    main()

Tested with python 3.7.3