College

CUNY School of Professional Studies

Course-Name

Software Application Programming I

Course-Code

IS 210

This week, we learn about a pillar of the pantheon of Python programming paradigms: exceptions. Throughout this assignment you will be challenged to both use and consider the use of exceptions as a control mechanisms withing your programs.

The following tasks will either have you interacting with existing files in the assignment repository or creating new ones on the fly. Don't forget to add your interpreter directive, utf-8 encoding, and a short docstring with any new files that you create!

In this exercise you'll be adding exception handling to a function that already exists.

1. Open task_01.py
2. Add exception handling to the simple_lookup() function so that attempts to access any index or key of var1 that do not exist will print a warning message and return var1
3. Allow all other exceptions to fail normally.

>>> simple_lookup([1,2], 4)
Warning: Your index/key doesn't exist.
[1,2]
>>> simple_lookup({}, 'banana')
Warning: Your index/key doesn't exist.
{}

In this exercise, you'll raise a manual exception when a condition is not met in a particular function. In particular, we'll be converting birth year to age.

1. Open task_02.py
2. Add a check that tests whether or not the person has a valid (0 or greater)
3. If the age is invalid, raise an InvalidAgeError

>>> get_age(2099)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
__main__.InvalidAgeError

The finally clause is particularly useful in handling cleanup tasks such as closing file descriptors or data streams.

1. Open task_03.py. This class represents a very simple logging class. Python offers much-better built-in loggers but this is a good teaching example.
2. Modify flush() so that any predictable errors are caught and are, themselves, logged.
   1. If the target logfile cannot be opened, log this fact then re-raise the error.
   2. Upon encountering any other IOError, log the error and stop loop loop processing (but continue with the rest of the program)
   3. Do not allow stored messages to be removed from the msgs object if they cannot be written to the disk.
   4. Allow msgs processing to continue as long as it doesn't encounter an IOError
   5. Upon encountering any other error, use the log() method to log the error encountered
3. Ensure that the close() method is called no matter what exceptions are encountered.

Code must be functional and pass tests before it will be eligible for credit.

Lint tests check your code for syntactic or stylistic errors To execute lint tests against a specific file, simply open a terminal in the same directory as your code repository and type:

$ pylint filename.py

Where filename.py is the name of the file you wish to lint test.

Unit tests check that your code performs the tested objectives. Unit tests may be executed individually by opening a terminal in the same directory as your code repository and typing:

$ nosetests tests/name_of_test.py

Where name_of_test.py is the name of the testfile found in the tests directory of your source code.

All tests may be run simultaneously by executing the runtests.sh script from the root of your assignment repository. To execute all tests, open a terminal in the same directory as your code repository and type:

$ ./runtests.sh

Code should be submitted to GitHub by means of opening a pull request.

As-of Lesson 02, each student will have a branch named after his or her GitHub username. Pull requests should be made against the branch that matches your GitHub username. Pull requests made against other branches will be closed. This work flow mimics the steps you took to open a pull request against the pull branch in Week Two.

For a refresher on how to open a pull request, please see homework instructions in Lesson 01. It is recommended that you run PyLint locally after each file is edited in order to reduce the number of errors found in testing.

In order to receive full credit you must complete the assignment as-instructed and without any violations (reported in the build status). There will be automated tests for this assignment to provide early feedback on program code.

When you have completed this assignment, please post the link to your pull request in the body of the assignment on Blackboard in order to receive credit.