Flash card challenge

Project
Write a flash card quizzer from scratch.

Goals

 * practice breaking down a problem and solving it in Python from scratch
 * practice command line option parsing
 * practice reading from files
 * practice working with dictionaries and for loops

Problem statement
Write a Python script that takes a file containing flash card questions and answers as an argument and quizzes the user based on the contents of that file until the user quits the program. Questions should be selected randomly (as opposed to going in order through the file), and the user should type in their guess. The script should say whether or not a guess is correct and provide the correct answer if an incorrect answer is given.

The file will contain flash card challenges in the form:

question,answer question,answer question,answer question,answer ...

For example, a state capitals flash card file might have the form:

Alabama,Montgomery Alaska,Juneau Arizona,Phoenix ...

Running the quizzer script with this file might look like this:

$ python quizzer.py state_capitals.txt Texas? Austin Correct! Nice job. New Mexico? Santa Fe Correct! Nice job. Oregon? Portland Incorrect. The correct answer is Salem. Virginia? Richmond Correct! Nice job. Virginia? Exit Goodbye

Step 1: Get the questions from a fixed flash card file
Download http://web.mit.edu/jesstess/www/IntermediatePythonWorkshop/state_capitals.txt.

Write the code to open and read  (we'll deal with getting a variable filename from the user later). Create a dictionary, where each comma-separated question and answer become a key and value in the dictionary. Note that each line in the file ends in a newline, which you'll need to remove from the word.

Step 1 resources:   File input and output: http://docs.python.org/tutorial/inputoutput.html#reading-and-writing-files.   Stripping characters (like whitespace and newlines) from a string: http://docs.python.org/library/stdtypes.html#str.strip.  

Step 2: Randomly select questions from the question dictionary
Write a  loop that loops forever and at each iteration through the loop randomly selects a key/value pair from the questions dictionary and prints the question.

To randomly select a key from the dictionary, you can use the  module, and in particular the   function.

When you run your script, to break out of the while loop you can press Control and then (while still holding down Control) c.

Step 2 resources:   loops: http://en.wikibooks.org/wiki/Python_Programming/Flow_control#While_loops   Dictionary manipulation: http://docs.python.org/tutorial/datastructures.html#dictionaries. In particular, look at getting a list of the dictionary's keys using the  method. </li> Selecting a random value from a list using the  module: http://docs.python.org/library/random.html#random.choice </li> </ul>

Step 3: Get and check the user's answer
Inside your  loop, write the code that gets an answer from the user and compares it to the answer retrieved from the questions dictionary. If the answer is correct, say so. If the answer is incorrect, say so and print the correct answer.

You can get input from a user using the  function.

It is up to you how strict you want to be with a user's answer. Do you want capitalization to matter?

Step 3 resources:   Using  to get data from the user: http://docs.python.org/library/functions.html#raw_input </li> </ul>

Step 4: Allow the user to quit the program
The  loop currently runs forever. Pick a special phrase (like "Exit") that the user can type instead of an answer that signals that they want to quit the program. When that special phrase is given, print a goodbye message and  out of the   loop to end the program.

Step 4 resources:   Using the  keyword to break out of a loop: http://docs.python.org/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops </li>  Making decisions with,  , and  : http://docs.python.org/tutorial/controlflow.html#if-statements </li> </ul>

Step 5: Get the quiz questions file from the user
Write the code to get the quiz questions file from a command line argument. Handle the case where a user forgets to supply a file; in this case, print an error message saying they need to supply a file, and then exit the program using the  function.

Step 5 resources:   Command line argument parsing: http://docs.python.org/library/argparse.html#module-argparse. </li>  Getting and checking the number of command line arguments: http://docs.python.org/library/sys.html. </li> </ul>

Checking your work
Try out your script on the following quiz files:


 * http://web.mit.edu/jesstess/IntermediatePythonWorkshop/metric.txt
 * http://web.mit.edu/jesstess/IntermediatePythonWorkshop/french_food.txt

Does your script handle the case where the user forgets to provide a filename?

Bonus challenge
Modify your script to quiz based on either the question or answer. e.g. for state capitals, the quizzer would present either a state, expecting its capital as the answer, or a capital, expecting its state as the answer.

Congratulations!
You've implemented a substantial, useful script in Python from scratch to help people study. Keep practicing!