i cant seem to figure out the error

[Jason Friedman]

>
>    - 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"`
>
>   def withdraw(self, amount):
>     self.amount=amount
>     if(amount > self.balance):
>       return ("Amount greater than available balance.")
>     else:
>   self.balance -= amount
>     return self.balance
>

The instructions say to "return 'invalid transaction'" but I expect they
really want that error printed to STDERR (typically your screen) rather
than literally returned.  Try this:

  def withdraw(self, amount):
    self.amount=amount
    if(amount > self.balance):
      print "Amount greater than available balance, no funds withdrawn."
    else:
      self.balance -= amount
    return self.balance