Python Dictionary

In my earlier article, I had covered Python Tuples.  In this article, I will be covering Python dictionary.

What is a Python dictionary?

A Python dictionary stores a List of key-value pairs.

Creating a Python dictionary

You can create a dictionary by specifying key-value pairs in curly brackets separated by commas. The following code demonstrates this:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}

This code creates a dictionary employeeDict with some key value pairs. The key and value need to be separated by a colon symbol(:)

Accessing values in a Python dictionary

You can access a value from a dictionary by specifying the key in square brackets. The following code demonstrates this:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}

print(employeeDict['name'])

Updating a Python dictionary

You can update the value for an existing key, add a new key-value pair or delete a key value pair.

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
employeeDict['department'] = 'Admin'
print(employeeDict['department'])

Updating value of an existing key

You can update the value of a key by specifying the key in square brackets and the value as shown below:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
employeeDict['department'] = 'Admin'

This code updates the department key to the value Admin

Adding a new key-value pair

You can also add a new key-value pair to the dictionary as shown below:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
employeeDict['manager'] = 'Sam Rocket'

This adds the key-value Manager:Sam Rocket to the dictionary.

Deleting a key-value pair

You can delete a key-value pair by using the del statement with the key name as shown below:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
del employeeDict['department']

This deletes the key-value corresponding to department

Deleting the entire dictionary

You can also delete the entire dictionary as shown below:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
del employeeDict

This deletes the entire employeeDict .So any attempt to access employeeDict after this would result in an error

Emptying a dictionary

You can clear a dictionary without deleting it by invoking the clearmethod as shown below:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
employeeDict.clear()

So, this empties the employeeDict dictionary but does not delete it. You can still add more values to the dictionary

Obtaining the length of a Python dictionary

Python has a built-in function len. This returns the length of the object passed in. You can use this function to obtain the length of a dictionary. The following code demonstrates this:

employeeDict1 = {'name':'John Doe','salary':5000.00,'department':'HR'}
print(len(employeeDict1))

Dictionary Methods

There are several dictionary methods that are useful. The following code demonstrates some of these methods:

employeeDict = {'name':'John Doe','salary':5000.00,'department':'HR'}
print('Keys:')
print(employeeDict.keys()); 

print('values:')
print(employeeDict.values());

print('Value for Salary:')
print(employeeDict.get('salary', 0))

print('Value for Manager:')
print(employeeDict.get('manager', 'Sam Rocket'))

• The keys()method returns the keys in the dictionary
• The values()method returns the values in the dictionary
• The get()method returns the value corresponding to the specified key if present, otherwise it returns a default value.

So, this code prints the following output:

Keys:
dict_keys(['name', 'salary', 'department'])
values:
dict_values(['John Doe', 5000.0, 'HR'])
Value for Salary:
5000.0
Value for Manager:
Sam Rocket

Further Learning

The Python Masterclass
Everything you need to know about Python
Python for beginners
Python for finance

Conclusion

So in this article, we understood what a Python dictionary is and how you can store key-value pairs in a dictionary. We also saw some of the common operations that you can perform on a dictionary. Finally, we saw some of the in-built dictionary methods.