10.2 Custom Class Account

  • Bank Account class that holds an account holder’s name and balance
    • An actual bank account class would likely include lots of other information

10.2.1 Test-Driving Class Account

  • Each new class you create becomes a new data type
  • Python is an extensible language
  • Before we look at class Account’s definition, let’s demonstrate its capabilities

Importing Classes Account and Decimal

  • Launch IPython from the ch10 examples folder, then import class Account
In [1]:
from account import Account
  • Account maintains and manipulates the account balance as a Decimal
In [2]:
from decimal import Decimal

Create an Account Object with a Constructor Expression

  • Create an object with a constructor expression that builds and initializes an object
  • Constructor expressions create new objects and initialize their data using argument(s) specified in parentheses
  • Parentheses following the class name are required, even if there are no arguments
In [3]:
account1 = Account('John Green', Decimal('50.00'))

Getting an Account’s Name and Balance

  • Access the Account object’s name and balance attributes
In [4]:
account1.name
Out[4]:
'John Green'
In [5]:
account1.balance
Out[5]:
Decimal('50.00')

Depositing Money into an Account

  • deposit method receives a positive dollar amount and adds it to the balance
In [6]:
account1.deposit(Decimal('25.53'))
In [7]:
account1.balance
Out[7]:
Decimal('75.53')

Account Methods Perform Validation

  • Account’s methods validate their arguments
In [8]:
account1.deposit(Decimal('-123.45'))

------------------------------------------------------------------------
ValueError                             Traceback (most recent call last)
<ipython-input-8-27dc468365a7> in <module>
----> 1 account1.deposit(Decimal('-123.45'))

~/Dropbox/books/2019/Python/PyCDS_JupyterSlides/ch10/account.py in deposit(self, amount)
     21         # if amount is less than 0.00, raise an exception
     22         if amount < Decimal('0.00'):
---> 23             raise ValueError('amount must be positive.')
     24 
     25         self.balance += amount

ValueError: amount must be positive.

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