Recurring monthly meetups are generally scheduled on the given weekday of a given week each month. In this exercise you will be given the recurring schedule, along with a month and year, and then asked to find the exact date of the meetup.

For example a meetup might be scheduled on the first Monday of every month. You might then be asked to find the date that this meetup will happen in January 2018. In other words, you need to determine the date of the first Monday of January 2018.

Similarly, you might be asked to find:

  • the third Tuesday of August 2019 (August 20, 2019)
  • the teenth Wednesday of May 2020 (May 13, 2020)
  • the fourth Sunday of July 2021 (July 25, 2021)
  • the last Thursday of November 2022 (November 24, 2022)

The descriptors you are expected to process are: first, second, third, fourth, last, teenth.

Note that descriptor teenth is a made-up word.

It refers to the seven numbers that end in '-teen' in English: 13, 14, 15, 16, 17, 18, and 19. But general descriptions of dates use ordinal numbers, e.g. the first Monday, the third Tuesday.

For the numbers ending in '-teen', that becomes:

  • 13th (thirteenth)
  • 14th (fourteenth)
  • 15th (fifteenth)
  • 16th (sixteenth)
  • 17th (seventeenth)
  • 18th (eighteenth)
  • 19th (nineteenth)

So there are seven numbers ending in '-teen'. And there are also seven weekdays (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday). Therefore, it is guaranteed that each day of the week (Monday, Tuesday, ...) will have exactly one numbered day ending with "teen" each month.

If asked to find the teenth Saturday of August, 1953 (or, alternately the "Saturteenth" of August, 1953), we need to look at the calendar for August 1953:

    August 1953
Su Mo Tu We Th Fr Sa
 2  3  4  5  6  7  8
 9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31

The Saturday that has a number ending in '-teen' is August 15, 1953.

Customizing and Raising Exceptions

Sometimes it is necessary to both customize and raise exceptions in your code. When you do this, you should always include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging.

Custom exceptions can be created through new exception classes (see classes for more detail.) that are typically subclasses of Exception.

For situations where you know the error source will be a derivative of a certain exception type, you can choose to inherit from one of the built in error types under the Exception class. When raising the error, you should still include a meaningful message.

This particular exercise requires that you create a custom exception to be raised/"thrown" when your meetup() function is given a weekday name and number combination that is invalid. The tests will only pass if you customize appropriate exceptions, raise those exceptions, and include appropriate error messages.

To customize a built-in exception, create a class that inherits from that exception. When raising the custom exception with a message, write the message as an argument to the exception type:

# subclassing the built-in ValueError to create MeetupDayException
class MeetupDayException(ValueError):
    """Exception raised when the Meetup weekday and count do not result in a valid date.

    message: explanation of the error.

    def __init__(self, message):
        self.message = message

# raising a MeetupDayException
raise MeetupDayException("That day does not exist.")
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