View source for OPS435 Python Assignment 1 2019 Fall

[[Category:OPS435-Python]][[Category:rchan]]
= Overview =
When making back up of data files or log files, it is a very common practice to name the backup directories and/or files based on the date the backup was done. In order to restore or locate the directory/file, we often need to find out the backup date from today's date.

The computational task for this assignment is to design an algorithm and write a python script according to your algorithm with appropriate functions. The script should take a date in the "YYYYMMDD" format and the number of days before or after the given date as the command line arguments, calculate and output to the standard output data channel the targeted date which is the number of day before or after the given date in the same format.

== Coding Standard ==
Your python script must follow the following coding guide:
* [https://www.python.org/dev/peps/pep-0008/ PEP-8 -- Style Guide for writing Python Code]
== Command Line Argument to be supported ==
* Name your python script as a1_[student_id].py, where [student_id] is your Seneca email user name.
* Your python script must support two mandatory command line arguments : (1) any valid date in YYYYMMDD format, (2) number of days before or after the given date, and one option flag: "--step"
* If there are less or more than two command line arguments given on the command line, your script should display the correct usage message and exit.

= Computation Requirements =
== Algorithm Design ==
* Write a step-by-step instructions in English on how to compute a date in "YYYYMMDD" format which is n days before or after a given date also in "YYYYMMDD" format.
* While you are working on the step-by-step instructions, note that there are different number of days in each month and some years have 365 days and some years have 366 days.
* You should also do some research to find out when we started using the Calendar in the current form. (This will pose a limit on the validity of your algorithm.)

== Required Modules and Functions ==
<b><font color='blue'>Your python script is allowed to import only the <u>os and sys</u> modules from the standard library and all the built-in functions.</font></b>

Based on the algorithm you have designed for this assignment, you should at least have the following three functions defined in your python script (see later section on the purpose of each function) in order to get a passing grade for this assignment:
* dbda()
* tomorrow()
* yesterday()
You should also create additional functions to improved the re-usability of your python code by adding the following functions to earn the maximum possible mark for this assignment:
* days_in_mon()
* leap_year()
* valid_date()
* usage()

== Documentation ==
* Please use python's docstring to document your python script (script level documentation) and each of the functions (function level documentation) you created for this assignment. The docstring should describle 'what' the function does, not 'how' it does.
* The following shows the docstring that was added to the tomorrow() function which provides the following information when called with help(tomorrow) in the python interactive shell:
<pre>
Help on function tomorrow in module rchan:

tomorrow(today) -> str
    tomorrow() takes a valid date string in 'YYYYMMDD' format and return a 
    date string for the next day in 'YYYYMMDD' format.
    e.g. tomorrow('20171231') -> '20180101'
         tomorrow('20180131') -> '20180201'
         tomorrow('20180228') -> '20180301'
(END)
</pre>

== Authorship Declaration ==
All your Python code for this assignment must be placed in a <font color='red'><b><u>single source python file</u></b></font>. Please include the following declaration <b><u>as part of the docstring</u></b> in your Python source code file (replace "Student Name" with your own name):
<source>OPS435 Assignment 1 - Winter 2019
Program: [student_id].py (replace student_id with your Seneca User name)
Author: "Student Name"
The python code in this file ([Student_id].py) is original work written by
"Student Name". No code in this file is copied from any other source 
except those provided by the course instructor, including any person, 
textbook, or on-line resource. I have not shared this python script 
with anyone or anything except for submission for grading.  
I understand that the Academic Honesty Policy will be enforced and 
violators will be reported and appropriate action will be taken.
</source>

== Tests and Test results ==
You must name your python 3 script as <code>a1_[Student_id].py</code>. The following examples assumes that the student_id is rchan.The script should accept two command line arguments, the first one is the date in "YYYYMMDD" format, and the second one is the number of day from the given date, a positive value indicates the number of days after the given date, and a negative value indicates the number of days before the given date. There is an optional flag called --step which can be provided at the command line that makes the program print out all dates until the target date. If the "YYYYMMDD" format is broken, your script should give an appropriate error message. Invalid months (>12) or invalid days of month(different for each month), should be detected and give appropriate error messages. For examples:
* <b><code>python3 a1_rchan.py 20180101 1</code></b>, and the output should be<br />
     20180102
* <b><code>python3 a1_rchan.py 20180101 -1</code></b>, and the output should be<br />
     20171231
* <b><code>python3 a1_rchan.py 20180101 2</code></b>, and the output should be<br />
     20180103
* <b><code>python3 a1_rchan.py --step 20180101 3</code></b>, and the output should be<br />
     20180102
     20180103
     20180104
* <b><code>python3 a1_rchan.py 20180701 500</code></b>, and the output should be<br />
     20191113
* <b><code>python3 a1_rchan.py 20189901 2</code></b>, and the output should be<br />
     Error: wrong month entered
* <b><code>python3 a1_rchan.py 20180199 2</code></b>, and the output should be<br />
     Error: wrong day entered
* <b><code>python3 a1_rchan.py 2018 2</code></b>, and the output should be<br />
     Error: wrong date entered

If there is too few or too many command line arguments given, display the proper usage:
* <code>Usage: a1_rchan.py [--step] YYYYMMDD +/-n</code>

== Script structure and sample template ==
Your code should all be in a single python file with at least the functions mentioned above: dbda(), tomorrow(), and yesterday(). To earn the maximum mark, you should also create additional functions into your algorithm, e.g.: leap_year(), days_in_mon, valid_date(), usage(), etc

The following is a brief description of each function:

* The dbda() function should be the main function of your script. The dbda() function will take a date in "YYYYMMDD" format, a positive or negative integer, and return a date either before or after the given date according to the value of the given integer in the same format. Your dbda() function should delegate the actual calculation of the target date to either the tomorrow() function or the yesterday() function. 
* The yesterday() function will take a date in "YYYYMMDD" format and return the date of the previous day in the same format.
* The tomorrow() function will take a date in "YYYYMMDD" format and return the date of the next day in the same format. Next paragraph is a sample python code for the tomorrow() function. To earn the maximum possible mark for the assignment, you should modify the sample tomorrow() function to make use of the days_in_mon() function.
* The leap_year() function will take a year in "YYYY" format, and return True if the given year is a leap year, otherwise return False.
* The valid_date() function will take a date in "YYYYMMDD" format, and return True if the given date is a valid date, otherwise return False. The valid_date() function should make use of the days_in_mon() function.
* The days_in_mon() function will take a year in "YYYY" format, and return a dictionary object which contains the total number of days in each month of the given year. The days_in_mon() function should make use of the leap_year() function.
* The usage() function will take no argument and return a string describing the usage of the script.
<pre>
     #!/usr/sbin/env python3
     import ...

     def tomorrow(today):
        ....
        return next_day

     def yesterday(today):
        ....
        return previous_day

     ....

     def dbda(yyyymmdd,days):
        ...
        setup loop
           call tomorrow or yesterday as appropriate
        return target_day

     if __name__ == "__main__":

     .. processing command line arguments ..
     .. call dbda() 
     ...
     output the expected date

</pre>     
 

=== Sample code for the tomorrow() function ===
<pre>
# Return the date in YYYYMMDD after the given day
# 
def tomorrow(today):
    if len(today) != 8:
       return '00000000'
    else:
       year = int(today[0:4])
       month = int(today[4:6])
       day = int(today[6:])

       lyear = year % 4
       if lyear == 0:
          feb_max = 29 # this is a leap year
       else:
          feb_max = 28 # this is not a leap year

       lyear = year % 100
       if lyear == 0:
          feb_max = 28 # this is not a leap year

       lyear = year % 400
       if lyear == 0:
          feb_max = 29 # this is a leap year

       tmp_day = day + 1 # tomorrow's day

       mon_max = { 1:31, 2:feb_max, 3:31, 4:30, 5:31, 6:30, 7:31, 8:31, 9:30, 10:31, 11:30, 12:31}
       if tmp_day > mon_max[month]:
          to_day = tmp_day % mon_max[month] # if tmp_day > this month's max, reset to 1
          tmp_month = month + 1
       else:
          to_day = tmp_day
          tmp_month = month + 0

       if tmp_month > 12:
           to_month = 1
           year = year + 1
       else:
           to_month = tmp_month + 0

       next_date = str(year)+str(to_month).zfill(2)+str(to_day).zfill(2)
     
       return next_date
</pre>

= Rubric =

{| class="wikitable" border="1"
! Task !!  Maximum mark !! Actual mark
|-
| Program Authorship Declaration ||5 ||
|-
| Program usage || 5 ||
|-
| Program Options --step || 5 ||
|-
| tomorrow() function || 5 ||
|-
| yesterday() function || 15 ||
|-
| dbda() function || 10 ||
|-
| script level docsting || 5 ||
|-
| leap_year() function || 10 ||
|-
| valid_date() function || 10 ||
|-
| days_in_mon() function || 10 ||
|-
| usage() function || 5 ||
|-
| Algorithm ||15||
|-
|'''Total''' || 100 || 

|}

= Assignment Due Date and submission procedure =

This Assignment is due on Friday, Feb 22, 2019 before mid-night. Please submit your algorithm (step-by-step instruction for solving the computation problem for this assignment in the English language), your python script, required test and test results to blackboard under the assignments section. Please refer to the detail submission instruction given on Blackboard.