Need help on a project To :"Create a class called BankAccount with the following parameters "

[lucasfrank254 at gmail.com]

On Saturday, December 12, 2015 at 1:05:29 AM UTC-8, Harbey Leke wrote:
> Create a class called BankAccount
> 
> .Create a constructor that takes in an integer and assigns this to a `balance` property.
> 
> .Create a method called `deposit` that takes in cash deposit amount and updates the balance accordingly.
> 
> .Create a method called `withdraw` that takes in cash withdrawal amount and updates the balance accordingly. if amount is greater than balance return `"invalid transaction"`
> 
> .Create a subclass MinimumBalanceAccount of the BankAccount class
> 
> Please i need help on this i am a beginer into python programming.
> 
> 
> Also below is a test case given for this project 
> 
> 
> import unittest
> class AccountBalanceTestCases(unittest.TestCase):
>   def setUp(self):
>     self.my_account = BankAccount(90)
>     
>   def test_balance(self):
>     self.assertEqual(self.my_account.balance, 90, msg='Account Balance Invalid')
>     
>   def test_deposit(self):
>     self.my_account.deposit(90)
>     self.assertEqual(self.my_account.balance, 180, msg='Deposit method inaccurate')
>     
>   def test_withdraw(self):
>     self.my_account.withdraw(40)
>     self.assertEqual(self.my_account.balance, 50, msg='Withdraw method inaccurate')
>     
>   def test_invalid_operation(self):
>     self.assertEqual(self.my_account.withdraw(1000), "invalid transaction", msg='Invalid transaction')
>   
>   def test_sub_class(self):
>     self.assertTrue(issubclass(MinimumBalanceAccount, BankAccount), msg='No true subclass of BankAccount')

my solution is:

class BankAccount(object):
    def __init__(self, initial_balance):
        self.balance = initial_balance
    def deposit(self, amount):
        self.balance +=amount
    def withdraw(self, amount):
          if self.balance>= amount:
              self.balance  -=  amount
          else:
            return invalid transaction
a1 = BankAccount (90)
a1.deposit(90)
a1.withdraw(40)
a1.withdraw(1000)
class MinimumBalanceAccount(BankAccount):
  def __init__(self):
    BankAccount.__init__(self,minimum_balance)
    self.minimum_balance = minimum_balance
    my_account = BankAccount(90)
    my_account.withdraw(40)
    print my_account.balance


It keeps alerting me that,"Error running your script".Where might I have gone wrong?Please help..