Working With JavaScript Object Defaults

The issue is a simple, yet annoying one. You want to access the property of an object, and work with that property value — perhaps calling a method on it, or accessing another property. The issue is that when an object property is undefined, errors happen. For example, if you're expecting a string or an array as a property value, the code would work fine if the property were initialized to an empty string, or an empty array respectively. The trick is, providing sane defaults on objects so that the clients using them don't blow up.

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()