The Account Assignment 7

The Account Assignment

decorators and properties

You are to create a file named Account.py containing the definition of two classes: Transaction and Account.  You must include some simple doctests for each.

The Transaction class that takes an amount, a date, a currency (default “USD”—U.S. dollars), a USD conversion rate (default 1), and a description (default None). All of the data attributes must be private. Provide the following read-only properties: amount, date, currency, usd_conversion_rate, description, and usd (calculated from amount*usd_conversion_rate). This class can be implemented in about sixty lines including some simple doctests.  

The Account class that holds an account number (account_number), an account name (account_name), and a list of Transactions. The account_number should be a read-only property; the account_name should be a read-write property with an assertion to ensure that the name is at least four characters long. The class should support the built-in len() function (returning the number of transactions), and should provide two calculated read-only properties: balance, which should return the account’s balance in USD and all_usd, which should return True if all the transactions are in USD and False otherwise. Three other methods should be provided: apply() to apply (add) a transaction, save(), and load(). The save() and load() methods should use a binary pickle with the filename being the account number with extension .acc; they should save and load a list containing the account number, the name, and transactions list. 

This class can be implemented in about ninety lines with some simple doctests that include saving and loading—use code such as 
     name = os.path.join(tempfile.gettempdir(), account_name) 
to provide a suitable temporary filename, and make sure you delete the temporary file after the
tests have finished.

Note: 

pickle command:

       fh = None
   try:
       data = <whatever you want to pickle
       fh = open(<your file name, "wb")
       pickle.dump(data, fh, pickle.HIGHEST_PROTOCOL)
   except (EnvironmentError, pickle.PicklingError) as err:
       raise SaveError(str(err))
   finally:
       if fh is not None:
           fh.close()

Obviously, you need to replace <whatever you want to pickle and <your file name with real strings. 
unpickle command:

       fh = None
   try:
            fh = open(<your file name, "rb")
      data = pickle.load(fh)
      # assert that number stored in the pickle matches self’s number
      extract name and Transactions
    except (EnvironmentError, pickle.UnpicklingError) as err:
            raise LoadError(str(err))
    finally:
      if fh is not None:
         fh.close()