How big is the dictionary?

Recall that we use the len() function to compute the number of characters in a string or to compute the number of elements in a list. For example,

>>> my_string = 'CS 515-A'
>>> len(my_string)
8

>>> my_list = ['Python', 'Java', 'C++', 'R']
>>> len(my_list)
4

The above code for a string and a list have in common that the len() function returns the number of items included in a given collection. We can use the len() function in a similar way for dictionaries as well, considering that a dictionary is a collection of key-value pairs.

Let’s take a look at the following dictionary that maps each type of member in our class with their respective numbers.

class_dict = {'instructors': 2, 'TAs': 10, 'tutors': 35, 'students': 600}

We can see that the dictonary class_dict consists of the following 4 key-value pairs:

• 'instructors': 2

• 'TAs': 10

• 'tutors': 35

• 'students': 600

Here is the output when we use the len() function.

>>> len(class_dict)
4

We are assured that the len() function accurately returns the number of key-value pairs in class_dict.