Methods for adding and deleting items

dict.update()

This method adds key-value pairs to the dictionary. The method takes in either another dictionary or an iterable (like a list) of key-value pairs and it adds those key-value pairs into the dictionary.

Consider our previous example class_dict:

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

Let’s add two more key-value pairs which gives the number of head tutors and the number of sections for this class to this dictionary. We can use the update() method to add the key-value pair as follows. As you can see below, we have used another dictionary containing the two key-value pairs as the input parameter for the update() method.

>>> new_entries_dict = {'head_tutors': 3, 'sections': 4}
>>> class_dict.update(new_entries_dict)

>>> class_dict
{'instructors': 2, 'TAs': 10, 'tutors': 35, 'students': 600, 'head_tutors': 3, 'sections': 4}

Alternatively, you can also use a list of two-value tuples as the input parameter to the update() method.

>>> new_entries_list = [('head_tutors', 3), ('sections', 4)]
>>> class_dict.update(new_entries_list)

>>> class_dict
{'instructors': 2, 'TAs': 10, 'tutors': 35, 'students': 600, 'head_tutors': 3, 'sections': 4}

dict.pop()

This method removes the key-value pair from the dictionary and returns its value. The input parameter to the method should be the key present in the dictionary.

Let’s delete the two newly added key-value pairs which give the number of head tutors and the number of sections for this class from the above dictionary. We need to provide the keys ‘head_tutors’ and ‘sections’ one after the other to delete them from the dictionary.

>>> class_dict
{'instructors': 2, 'TAs': 10, 'tutors': 35, 'students': 600, 'head_tutors': 3, 'sections': 4}

>>> class_dict.pop('head_tutors')
3

>>> class_dict
{'instructors': 2, 'TAs': 10, 'tutors': 35, 'students': 600, 'sections': 4}

>>> class_dict.pop('sections')
4

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

As you can see above, the pop() method returns the value that was associated with the key given as the input parameter. When we print the class_dict dictionary again, we see that the key-value pair associated with key given as input parameter is deleted.