In this section, we're going to learn about dictionaries. A dictionary is similar to a list in that they both hold multiple values at a time, but they differ in some important ways. In a list, each value is accessed using its index, which is automatically assigned as you add new elements. With a dictionary, elements are accessed using their keys, which the programmer creates as they build the dictionary.

To create a dictionary in Python, we use a pair of curly braces, and just like with a list, we can either leave them empty to create an empty dictionary, or initialize it with data:

empty_dict = {}
student = {"name": "Tom", "age": 17, "height": 68}

Each item in the dictionary consists of a key/value pair separated by a colon, and each pair is separated by a comma. The item before the colon is the key, and the item after the colon is the value.

To access a particular value, we use the same square brackets as we would with a list, except we put the corresponding key instead of an index:

print(student["age"])
# 17

To add an element to the dictionary, we pretend as though the key we want to use already exists, and assign it a value with the equals operator:

student["year"] = 11
print(student["year"])
# 11

If the key does exist already, the existing value will be updated, and no new keys will be added:

student["age"] = 18
print(student["age"])
# 18

To check if the dictionary contains a particular key, we can use in, just like we would with a list:

print("name" in student) # True
print("grade" in student) # False

We delete a key/value pair the same way we would delete an element in a list, using the del keyword:

del student["height"]
print(student["height"])

# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# KeyError: 'height'