title: How to initialize key,value pair in dictionary with lambda expression?
body: <p>I have a dictionary where key is a tuple (class,word). I want to initialize the value of dictionary for a particular class, irrespective of the word to a particular default value.
  Eg: dict = defaultdict(lambda : -1.0)</p>
  
  <p>dict [('A', any word here)] = some constant value according to lambda expression</p>
  
  <p>Here of the tuple ('A', any word here)- A is the class while "any word here" can be any random unknown word.
  This was my attempt, but am unable to figure out the correct way:
  dict = defaultdict(lambda tag, x: some_constant)).</p>
  
  <p>How to I make x a placeholder that might come in its place?</p>