Fetching Backbone Models The Safe Way

If you're using Backbone, odds are that you have several detail views for various types of objects. Before those views are rendered, you need to ensure that model has been fetched. Otherwise, you don't have anything to render, besides the template, perhaps with placeholders filling in for the real model data. Or maybe your application has already performed a fetch on the collection, in which case, we have all the data required to render the detail view of the model. But, unless you're keeping that collection synchronized, you could be rendering stale data.

Python Dictionary get()

Python dictionary instances have a built in get() method that will return the value of the specified key. The method also accepts a default value to return should the key not exist. Using this method to access dictionary values is handy when you want to set a default. The alternative methods are to either manually test if the key exists or to handle a KeyError exception. The three methods are outlined below.

def use_get():
   dict_obj = dict(a=1, b=2)
   return dict_obj.get("c", 3)

def use_has_key():
   dict_obj = dict(a=1, b=2)
   if dict_obj.has_key("c"):
       return dict_obj["c"]
   else:
       return 3
  
def use_key_error():
   dict_obj = dict(a=1, b=2)
   try:
       return dict_obj["c"]
   except KeyError:
       return 3
  
if __name__ == "__main__":
   print "USE GET:", use_get()
   print "HAS KEY:", use_has_key()
   print "KEY ERROR:", use_key_error()