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Learning Objectives ​

  • Understand how to Create, Read, Update & Delete elements in a dictionary using various Python methods & special syntax

Working with Dictionaries (CRUD) ​

In order to build more complex applications, we need to understand how to perform the 4 main operations of handling data:

  • Create
  • Read
  • Update
  • Delete

Creating a Dictionary ​

A dictionary in Python is a collection of key-value pairs where each key is unique.

Keys and their associated values are wrapped in curly braces and separated by commas.

python
student_info = {'name': 'John', 
                'age': 16,
                'grade': '10th'}

Reading a Dictionary ​

We can access the value associated with a specific key in a dictionary by using the .get() method.

The .get() method takes in one argument, which is the name of the key.

python
student_info = {'name': 'John', 
                'age': 16,
                'grade': '10th'}
print(student_info.get('name'))
print(student_info.get('age'))

Output:

python
John
16

[ ] vs `.get()`

We can access dictionary elements by using square brackets with the key name, (e.g.student_info['name'])

However, using .get() is preferred because it doesn't cause an error if the key doesn't exist; it simply returns None.

In contrast, using square brackets with an invalid key will raise a KeyError and stop code execution

Updating a Dictionary ​

Update Method ​

We can update or add key-value pairs in a dictionary using the .update() method.

The .update() method takes in a dictionary as an argument where you can specify the key-value pair to be added or updated.

python
student_info = {'name': 'John', 
                'age': 16,
                'grade': '10th'}
student_info.update({'age': 17})
print(student_info)

Output:

python
{'name': 'John', 'age': 17, 'grade': '10th'}

Adding a New Key-Value Pair ​

To add a new key-value pair, we simply assign a value to a new key in the dictionary.

python
student_info = {'name': 'John', 
                'age': 16, 
                'grade': '10th'}
student_info['school'] = 'High School'
print(student_info)

Output:

python
{'name': 'John', 'age': 16, 'grade': '10th', 'school': 'High School'}

Deleting from a Dictionary ​

There are two main ways to delete elements from a dictionary: using the .pop() method or the del keyword.

Pop Method ​

The .pop() method removes the key-value pair associated with the specified key and returns the value.

python
student_info = {'name': 'John', 
                'age': 16, 
                'grade': '10th'}
student_info.pop('age')
print(student_info)

Output:

python
{'name': 'John', 'grade': '10th'}

Del Keyword ​

The del keyword can be used to delete a key-value pair from a dictionary.

python
student_info = {'name': 'John', 
                'age': 16, 
                'grade': '10th'}
del student_info['grade']
print(student_info)

Output:

python
{'name': 'John', 'age': 16}

Del Trick

If you want to delete the entire dictionary, use del dictionary_name.