parameters: (self, callback, existing=True)
docstring: Invoke `callback` for all distributions
  
          If `existing=True` (default),
          call on all existing ones, as well.
docstring_summary: Invoke `callback` for all distributions
docstring_tokens: Invoke callback for all distributions
function: def subscribe(self, callback, existing=True):
          """Invoke `callback` for all distributions
  
          If `existing=True` (default),
          call on all existing ones, as well.
          """
          if callback in self.callbacks:
              return
          self.callbacks.append(callback)
          if not existing:
              return
          for dist in self:
              callback(dist)
function_tokens: def subscribe ( self , callback , existing = True ) : if callback in self . callbacks : return self . callbacks . append ( callback ) if not existing : return for dist in self : callback ( dist )