A common use of dictionaries is to count the occurrences of like items in a sequence; a typical example is counting the occurrences of words in a body of text. The following code creates a dictionary where each word in the text is used as a key and the number of occurrences as its value. This uses a very common idiom of nested loops. Here we are using it to traverse the lines in a file in an outer loop and the keys of a dictionary on the inner loop:

def wordcount(fname):  
   try: 
        fhand=open(fname) 
   except:
        print('File can not be opened') 
        exit() 

   count=dict() 
   for line in fhand: 
        words=line.split() 
        for word in words: 
            if word not in count: 
                count[word]=1  
            else: 
                count[word]+=1 
   return(count)

This will return a dictionary with an element for...