Reshma Bidikar

In myearlier 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.