Test records

record_taker.py

import datetime
import os

class Checker(object):
    """ Holder class for all checking/parsing
    """

    @staticmethod
    def try_int(number):
        try:
            return int(number)
        except ValueError:
            return None

    @staticmethod
    def is_valid_date(date):
        # try:
        #   d,m,y = date.split('/')
        # except ValueError:
        #   return None
        # if any(map(lambda _: try_int(_) is not None), [d,m,y]):
        #   return None

        # decided to use inbuilt function as it does all the work of checking the date 
        try:
            return datetime.datetime.strptime(date, "%m/%d/%Y").strftime("%m/%d/%Y")
        except ValueError:
            return None

class Worker(object):
    def __init__(self):
        self.student_ids  = set()   # stores all the student ids to prevent duplication. set for O(1) lookup
        
        # creates file first if it does not exist
        if not os.path.exists('records.txt'):
            open('records.txt', 'w').close() 

        # saving all the ids of all students which were added in the previous sessions
        self.records_file = open('records.txt', 'r')
        for x in self.records_file.read().split('\n'):
            x = x.strip()
            if x == '': continue
            self.student_ids.add(int(x.split(', ')[0]))
        self.records_file.close()

        self.records_file = open('records.txt', 'a')

    # class private method so that it can't be used publicly
    def _add_to_file(self, *args):
        prepared_line = ", ".join(map(str, args))
        self.records_file.write(prepared_line)
        self.records_file.write("\n")
        print "Added info to file: %s" % prepared_line

    # ensures that input is not an empty string
    def get_complete_string(self, what_to_ask):
        while True:
            print "Enter the %s: " % (what_to_ask,),
            temp = raw_input().strip()
            if temp == '':
                print "The field '%s' can't be left empty!" % what_to_ask.upper()
            else: return temp

    def add_student(self):

        while True:
            s_id = self.get_complete_string('student ID')
            s_id = Checker.try_int(s_id)
            if s_id is not None and s_id > 0:
                if s_id not in self.student_ids:
                    self.student_ids.add(s_id)
                    break
                else: print "A student with this ID already exists"
            else: print "The student ID should be a natural number"

        # going to allow s_fname, s_lname, s_course to have numbers in
        # their values as I'm not sure whether I should allow or not
        s_fname  = self.get_complete_string("first name")
        s_lname  = self.get_complete_string("last name")
        s_course = self.get_complete_string("course")

        while True:
            s_date = self.get_complete_string("date of completion")
            if Checker.is_valid_date(s_date) is not None: break
            print "Date of completion format is invalid. Please enter date in MM/DD/YYYY format."

        self._add_to_file(s_id, s_fname, s_lname, s_course, s_date)

    def _exit(self):
        print "\nExiting gracefully."
        print "Have a great ANRC day!"
        self.records_file.close()
        exit()

    def work(self):
        print """
        ANRC Student Record Taker.
                Hello!"""

        command_handlers = {'ADD': self.add_student, 'QUIT': self._exit}
        while True:
            print "\nPlease select whether you want to <ADD> a record or <QUIT>: ",
            _ = raw_input().strip().upper()

            handler = command_handlers.get(_, None)
            if handler is None:
                print "Invalid option: %s." % _
                continue

            if callable(handler):
                handler()
            else: raise ValueError("The programmer messed up somehow!")

def main():
    # try:
        worker = Worker()
        worker.work()
    # except Exception as e:
    #   print "An unhandled exception was raised: %s", e

if __name__ == '__main__':
    main()

seed_records.txt

1003, Nathan, Swaim, Python Programming, 11/19/2010
1023, Joe, Black, Java Programming, 03/05/2009
1007, Chris, Farley, Basic Malware Analysis, 06/27/2008
1003, Nathan, Swaim, O/S Fundamentals, 04/28/2007
2015, Sambhav, Satija, Python Programming, 03/29/1995

student_records.py

import os

def try_int(number):
    try:
        return int(number)
    except ValueError:
        return None

class Record(object):
    def __init__(self, _id, fname, lname, course, date):
        self.s_id   = int(_id.strip())
        self.fname  = fname.strip()
        self.lname  = lname.strip()
        self.course = course.strip()
        self.date   = date.strip()

    # so that I simply have to write print student
    def __str__(self):
        return  """
Student ID: %(id)s
    name  : %(name)s
    course: %(course)s
    date of completion: %(date)s 
""" % {'id': self.s_id, 'name': " ".join([self.fname, self.lname]),
        'course': self.course, 'date': self.date}

class Worker(object):
    def __init__(self):
        self.students  = [] # stores all the students

        if not os.path.exists('records.txt'):
            print "'records.txt' does not exist"
            exit()

        self.records_file = open('records.txt', 'r')
        for x in self.records_file.read().split('\n'):
            x = x.strip()
            if x == '': continue

            self.students.append(Record(*x.split(', '))) # will work because of tuple/list unpacking
        
        self.records_file.close()

    def list_all_students(self):
        print "Listing all %d students." % len(self.students)
        for _ in self.students: print _

    def get_student_by_id(self):
        while True:
            print "Enter ID of student: ",
            _id = try_int(raw_input().strip())
            if _id is not None and _id > 0: break
            print "Please enter a natural number as an ID"

        results = [_ for _ in self.students if _.s_id == _id]
        if not any(results) or len(results) == 0:
            print "No student exists with ID: %d." % _id
            return

        print results[0]

    def get_students_by_courses(self):
        while True:
            print "Enter course name: ",
            course = raw_input().strip().lower()
            if course != '': break
            print "Please enter a course name to search for."

        results = [_ for _ in self.students if _.course.lower() == course]
        if len(results) == 0:
            print "No student records found with course matching '%s'." % course
            return

        for _ in results: print _

    def work(self):
        print """
        ANRC Student Records Reader.
                Hello!"""

        command_handlers = {'1': self.list_all_students,
                            '2': self.get_student_by_id,
                            '3': self.get_students_by_courses,
                            '4': self._exit}
        while True:
            print """

1. List all student records in the records records_file
2. Display record for a specific student ID. Only the first matching is shown
3. Display all records for a specific completed course
4. Exit the system

Option:""", 
            _ = raw_input().strip().upper()

            handler = command_handlers.get(_, None)
            if handler is None:
                print "Invalid option: %s." % _
                continue

            if callable(handler):
                handler()
            else: raise ValueError("The programmer messed up somehow!")

    def _exit(self):
        print "Have a great ANRC day!"
        exit()

def main():
    worker = Worker()
    worker.work()

if __name__ == '__main__': main()

Ensure to keep a trailing new line in the seed_records.txt while copying.