BankAccount

I'd like you to make a class that represents a bank account.

Your bank account should accept an optional balance argument (defaulting to 0), have a balance attribute, and have deposit, withdraw, and transfer methods:

>>> a1 = BankAccount()
>>> a1.balance
0
>>> a1.deposit(10)
>>> a1.balance
10
>>> a2 = BankAccount(balance=20)
>>> a2.withdraw(15)
>>> a2.balance
5
>>> a1.transfer(a2, 3)
>>> a1
BankAccount(balance=7)
>>> a2
BankAccount(balance=8)

Your bank account should also have a nice string representation (as shown above).

This example might not seem realistic (it's not) but it's a classic example for good reason:

1. most real-world object-oriented programming in Python involves a lot of code (classes aren't usually worth the complexity until you have a sufficiently complex problem)
2. a bank account is a pretty common and familiar concept which doesn't require a lot of domain-specific knowledge

Bonus 1