CSc 120: Dates

Background

Restrictions

1. For the long problems, your code should follow the style guidelines for the class. The long problem specification details the commenting requirements for methods.
2. You may not use concepts and/or short-hand syntax not yet covered in class. The restrictions include the following:
   list (or dictionary) comprehensions, e.g., [n * 2 for i in range(10)]
   • with open (explicitly open and close the file instead)
   • the ternary operator (use an if instead)
   • nested functions (using def within a function to define another function)
   • recursion
   • exceptions and asssertions
   • type annotations
   • lambda expressions
   • generators and user defined iterators
   • importing libraries (unless a library is explicitly mentioned in the specification)

Problem Description

Suppose you wanted to offer a website or app to manage a database of dates and events. Such a database might be used to look up dates in the past ("on this date in history...", as in the sites mentioned above); or they might be used as a calendar service to provide reminders for future events. In either case, you need a program that can record and look up strings (i.e., events) associated with dates.

One catch here is that people use many different formats to write dates, e.g., "December 25, 2021", "2021-12-25", and "12/25/2021", all of which represent the same date. The format that was used to insert an event into the database may or may not be the same as the format that will be used to look up that date. Your program therefore needs a way to process dates in different formats and recognize when dates in different formats are equivalent. To that end, this programming assignment involves writing a class to maintain information about dates and events and to recognize dates in different formats. The program will read a file containing a series of operations, where each operation refers to a database of dates and events, and will process each operation in turn.

Input Formats

I   Date :   Event
R   Date

The Date and Event fields in the operation line are as follows:

Date

This specifies a date. It can be in any of the following three formats.

• yyyy-mm-dd, where yyyy is a 4-digit sequence giving the year; mm is a 1- or 2-digit sequence giving the month; and dd is a 1- or 2-digit sequence giving the date.

  Example: 2017-02-31

• mm/dd/yyyy, where yyyy is a 4-digit sequence giving the year; mm is a 1- or 2-digit sequence giving the month; and dd is a 1- or 2-digit sequence giving the date.

  Example: 02/31/2017.

• MonthName   dd   yyyy, where MonthName is a three-letter sequence giving the name of a month (one of: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec); dd is a 1- or 2-digit sequence giving the date; and yyyy is a 4-digit sequence giving the year.

  Example: Feb 31 2017

NOTE: To simplify programming, we will assume that all months have 31 days.

Event

This is a string starting at the first non-whitespace character after the colon ":" following the date and going as far as the end of the line.

Examples of operations are:

I   2017-01-16 :  Martin Luther King Day
I   Mar 31 1997: Arizona Wildcats win National Basketball Title
R   03/31/1997

The first of these inserts the event "Martin Luther King Day" for the date Jan 16, 2017 into the calendar. The second adds the event "Arizona Wildcats win National Basketball Title" for the date March 31, 1997. The third item retrieves and prints out all events for the date March 31, 1997.

NOTE: The event may also contain the colon character ":", as shown in the Examples section (see Example 4 in that section). Be sure to consider that when you are parsing the input line.

Expected Behavior

Write a Python program, in a file dates.py, that maintains a collection of Date objects, each of which has associated with it a sequence of strings that refer to events for that date, processing these objects in accordance with operations read from an input file. Your program should behave as follows:

1. Use input() (without any argument) to read the name of an input file.
2. Read the file specified and process the operation given on each line as follows:
   • OpType = I. Add the Event string to the collection of events for the date specified (duplicates are OK). If there is no existing Date object for that date, create one and initialize its collection of events to the Event string specified.
   • OpType = R. Print out the event strings for that date one per line (see Output Format below). If there is no existing Date object for that date, do not print anything.
   • If the OpType is not a valid operation, print an error message (see Errors below).

Dates are considered equal if their canonical representations (see below) are the same.

Some examples of input files and generated output are shown here.

Canonical Representation of Dates

"{:d}-{:d}-{:d}".format( int(yyyy ), int(mm), int(dd))

The reason for converting yyyy, mm, and dd to numbers using int() and then back to strings is to remove any leading zeros.

Example:

Input format	Canonical representation
Mar 7 1997 Mar 07 1997 03/07/1997 3/7/1997 1997-3-07 1997-03-7	1997-3-7

Output Format

print("{}: {}".format(date_canonical, event))

Programming Requirements

class Date

An instance of this class describes a date.

Attributes: These should include:

• a string representing the canonical representation of the date
• the associated events (a collection of strings, e.g., a list or set).

Methods: These should include:

• __init__(self, date_str, event), where date_str is a string of the date (in its canonical representation) event is a string for an event
• Getter methods for the attributes
• add_event(self, event), where event is a string for an event; this method adds event to the collection of events for a Date object
• __str__(self), which returns a string representation of a Date object

class DateSet

An instance of this class describes a collection of dates.

Attributes: These should include:

• a dictionary of Date objects. (Consider what might you use as keys.)

Methods: These should include:

• __init__(self), which creates an empty dictionary to hold Date objects
• add_date(self, date_str, event), where date_str is a string and eventis a string. If the date is not in the collection, a new Date object is created and added to the collection. If the date is already in the collection, the event is added to the Date object.
• __str__(self), which returns a string representation of a DateSet object

Additionally, you will need code for the following:

• To read in an input file name (use input() without arguments), read a series of operations from this file (see Input Formats above), and process them as specified under Expected Behavior above. You can put this code in a function that is not within any class (just like main()).
• To convert a date string to canonical format. (You can use your solution to the short problem.) You can put this code in a function that is not within any class (just like main()).

Your program should be appropriately modularized. In particular, other than the code mentioned above for processing input and converting dates to their canonical form, your code should be placed in methods in the appropriate class.

Error Output

   “Error - Illegal operation.“  

Commenting

Examples