Looping over dictionaries#

1. Using the `in` keyword for a `for` loop#

We have learned in previous lessons that for loops with a dictionary can iterate over each key in the dictionary. With our example class_dict, we can repeatedly print the keys with a for loop.

class_dict = {'instructors': 2, 'TAs':10, 'tutors':35, 'students': 600}
for member in class_dict:
    print(member)

Here is the output of the keys printed.

instructors
TAs
tutors
students

In case that we want to print the values instead of the keys, our code can be edited as

class_dict = {'instructors': 2, 'TAs':10, 'tutors':35, 'students': 600}
for member in class_dict:
    print(class_dict[member])

and the output is as follows.

2. Dictionary methods for repetitive access of contents#

However, we can use dictionary methods to iteratively access keys, values, or their pairs.

dict.keys()#

The keys() method returns a collection of keys in the dictionary that the method is called upon. Therefore, we can use a for loop and the keys() method to access every key as follows:

class_dict = {'instructors': 2, 'TAs':10, 'tutors':35, 'students': 600}
for member in class_dict.keys():
    print(member)

The output is given as

instructors
TAs
tutors
students

dict.values()#

The values() method can be utilized in the same format to access corresponding values in the given dictionary. It returns a collection of values in the dictionary, and accordingly, using a for loop with the values() method enables to handle every value in the dictionary.

class_dict = {'instructors': 2, 'TAs':10, 'tutors':35, 'students': 600}
for num in class_dict.values():
    print(num)

Here is the output.

This is useful when we are required to print every value in the dictionary.

dict.items()#

What if it is necessary to acknowledge in the output which key is associated to each value? The items() method comes in handy when we want to access every key-value pair. It returns a collection of every pair in the dictionary, where each pair is a tuple of a key and a value.

class_dict = {'instructors': 2, 'TAs':10, 'tutors':35, 'students': 600}
for num in class_dict.items():
    print(pair)

The output of this for loop is

('instructors', 2)
('TAs', 10)
('tutors', 35)
('students', 600)

Looping over dictionaries

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