old_contents: from rx.core import Observable, AnonymousObservable
  
  from rx.concurrency import current_thread_scheduler
  from rx.internal import extensionclassmethod
  
  
  @extensionclassmethod(Observable, alias="just")
  def return_value(cls, value, scheduler=None):
      """Returns an observable sequence that contains a single element,
      using the specified scheduler to send out observer messages.
      There is an alias called 'just'.
  
      example
      res = rx.Observable.return(42)
      res = rx.Observable.return(42, rx.Scheduler.timeout)
  
      Keyword arguments:
      value -- Single element in the resulting observable sequence.
      scheduler -- [Optional] Scheduler to send the single element on. If
          not specified, defaults to Scheduler.immediate.
  
      Returns an observable sequence containing the single specified
      element.
      """
  
      scheduler = scheduler or current_thread_scheduler
  
      def subscribe(observer):
          def action(scheduler, state=None):
              observer.on_next(value)
              observer.on_completed()
  
          return scheduler.schedule(action)
      return AnonymousObservable(subscribe)
  
new_contents: from rx.core import Observable, AnonymousObservable
  
  from rx.concurrency import current_thread_scheduler
  from rx.internal import extensionclassmethod
  
  
  @extensionclassmethod(Observable, alias="just")
  def return_value(cls, value, scheduler=None):
      """Returns an observable sequence that contains a single element,
      using the specified scheduler to send out observer messages.
      There is an alias called 'just'.
  
      example
      res = rx.Observable.return(42)
      res = rx.Observable.return(42, rx.Scheduler.timeout)
  
      Keyword arguments:
      value -- Single element in the resulting observable sequence.
      scheduler -- [Optional] Scheduler to send the single element on. If
          not specified, defaults to Scheduler.immediate.
  
      Returns an observable sequence containing the single specified
      element.
      """
  
      scheduler = scheduler or current_thread_scheduler
  
      def subscribe(observer):
          def action(scheduler, state=None):
              observer.on_next(value)
              observer.on_completed()
  
          return scheduler.schedule(action)
      return AnonymousObservable(subscribe)
  
  
  @extensionclassmethod(Observable)
  def from_callable(cls, supplier, scheduler=None):
      """Returns an observable sequence that contains a single element generate from a supplier,
         using the specified scheduler to send out observer messages.
  
         example
         res = rx.Observable.from_callable(lambda: calculate_value())
         res = rx.Observable.from_callable(lambda: 1 / 0) # emits an error
  
         Keyword arguments:
         value -- Single element in the resulting observable sequence.
         scheduler -- [Optional] Scheduler to send the single element on. If
             not specified, defaults to Scheduler.immediate.
  
         Returns an observable sequence containing the single specified
         element derived from the supplier
         """
      scheduler = scheduler or current_thread_scheduler
  
      def subscribe(observer):
          def action(scheduler, state=None):
              try:
                  observer.on_next(supplier())
                  observer.on_completed()
              except Exception:
                  observer.on_error(Exception)
          return scheduler.schedule(action)
  
      return AnonymousObservable(subscribe)
subject: implement from_callable