Adventures in Machine Learning

Mastering User Management and Set Operations in Django and Python

Managing user access and enforcing proper permissions is an essential part of any web development project. Django, a popular web framework, provides several built-in features to simplify user management and authentication.

In this article, we will explore various topics related to user management and authentication in Django, including model permissions, enforcing permissions, implementing custom roles, and built-in authentication systems. Model Permissions:

Model permissions are an essential feature in Django that allow developers to restrict or grant access to specific models and their data.

This type of permission is highly granular and can be customized according to the specific needs of an application. The four primary actions that can be controlled by model permissions are add, delete, change, and view.

For example, a developer can set up a model permission that only allows certain users to add new data to a particular model and doesn’t allow them to delete or change existing data. Django provides a mechanism to specify default permissions for all models in an application, but the permissions can be overridden for individual models or even specific user accounts.

Enforcing Permissions:

While model permissions control who can perform specific actions on a model, enforcing permissions ensures that those permissions are respected at the view layer. Django provides several built-in decorators and shortcuts to enforce permissions, such as the `@login_required` decorator, which requires users to be authenticated before accessing a view.

Another useful shortcut is the `user_passes_test` decorator, which allows developers to create custom tests to check if a user is authorized to access a view. If a user doesn’t satisfy the tests, they are redirected to a specified URL or shown an HTTP 404 page.

Implement Custom Business Roles:

Django’s built-in User model provides basic authentication and authorization functionality, but it may not always be sufficient for complex applications. In such cases, developers need to implement custom business roles to enforce specific access restrictions and user permissions.

One approach to implement custom business roles is to create custom fields in the User model that define the specific roles of each user. Then, create a two-step form for users to update their profile, where they can select their role(s).

Finally, write view decorators that enforce permissions based on a user’s roles. Grant Permissions Only Using Groups:

Groups are a built-in feature in Django that allow developers to group users together and assign permissions to the group instead of individual users.

This approach simplifies permission management, especially in large organizations with multiple teams or departments. For example, a web application may have a group named “Marketing,” which contains all the users with marketing responsibilities.

Then, specific permissions can be granted to this group, such as creating or modifying marketing campaigns. This mechanism eliminates the need to manage permissions individually for each user.

Prevent Non-Superusers From Editing Their Own Permissions:

In Django, staff users can edit the permissions of other users, which can be a security vulnerability if misused. By default, Django allows staff users to edit their own permissions, which can lead to privilege escalation and unauthorized data access.

To prevent this, developers should remove the ‘change_permission’ permission from the staff user’s permissions and create a custom view that only allows superusers to edit the permissions of staff users. Additionally, all sensitive fields, such as email addresses and passwords, should be accessible only to superusers.

Override Permissions:

Django’s built-in permissions system provides a powerful way of granting access to specific models, but it may not be suitable for all applications. In such cases, developers may need to override permissions at the object level.

By defining custom hooks, developers can control which users have permission to create, view, update, or delete an object. For example, a developer can implement an override hook that checks if a user is a member of a specific group before allowing them to create or modify an object.

Restrict Access to Custom Actions:

Django provides several built-in actions in the admin interface, such as “delete selected objects” or “export to CSV.” However, developers may need to create custom actions to perform specific tasks, especially for non-admin users. In such cases, it’s essential to restrict access to these custom actions to authorized users only.

Developers can create a custom decorator that checks if a user is an admin user and returns a 403 error if not. Additionally, it’s important to include proper validation for input fields to prevent unauthorized data manipulation.


In conclusion, Django provides a range of built-in features to manage user access and authentication, but it’s essential to customize these mechanisms to fit the specific needs of an application. By properly implementing model permissions, enforcing permissions at the view layer, and implementing custom business roles, developers can ensure that users’ data and privacy are protected.

By using groups and restricting access to sensitive permissions, developers can prevent unauthorized access and data breaches. Finally, by overriding permissions and restricting access to custom actions, developers can ensure that only authorized users can perform certain actions in an application.

Sets in Python:

A set is a built-in data structure in Python that represents an unordered collection of unique elements. Sets are a useful tool for various operations such as eliminating duplicates from a list or finding the intersection between two collections.

Implementing a set in Python is easy, as all we need to do is create a set object and pass any iterable as an argument to the constructor. We can create a set by initializing an empty set object using curly braces {} or by using the set() constructor.

For example, the following code creates a set with some initial values:


>>> my_set = {1, 2, 3, 4, 5}

>>> print(my_set)

{1, 2, 3, 4, 5}


Adding elements to a set can be done using the `add()` method. For example:


>>> my_set.add(6)

>>> print(my_set)

{1, 2, 3, 4, 5, 6}


Sets also provide various methods to perform operations such as union, intersection, difference, and symmetric difference.

To perform a union operation between two sets, we can use the `|` operator or the `union()` method. Similarly, we can use the `&` operator or the `intersection()` method to find the intersection between two sets, and the `-` operator or the `difference()` method to find the difference between two sets.

For example:


>>> set1 = {1, 2, 3, 4, 5, 6}

>>> set2 = {4, 5, 6, 7, 8, 9}

>>> print(set1 | set2)

{1, 2, 3, 4, 5, 6, 7, 8, 9}

>>> print(set1 & set2)

{4, 5, 6}

>>> print(set1 – set2)

{1, 2, 3}


In addition to the methods mentioned, sets also provide various methods to add or remove elements, check if an element exists in the set, or iterate over the set. Python KeyError Exceptions and How to Handle Them:

A KeyError exception occurs when we try to access a key in a dictionary that doesn’t exist.

Accessing a non-existent key in a dictionary will raise a KeyError exception, which can cause the program to terminate or behave unexpectedly. Handling these exceptions is essential to ensure that our programs work as intended.

One common way to handle a KeyError is by using a try-except block. We can wrap the code that attempts to access the dictionary in a try block and catch the KeyError exception in the except block.

In the except block, we can handle the exception by providing a default value or printing an error message. For example, let’s say we have a dictionary of student names and their grades:


>>> grades = {‘John’: 80, ‘Sarah’: 90, ‘Lisa’: 85}


Now, let’s say we want to get the grade of a student named ‘Michael’, who is not in the dictionary.

If we try to access the dictionary using this key, we will get a KeyError exception:


>>> grades[‘Michael’]

KeyError: ‘Michael’


To handle this exception, we can use a try-except block, as follows:



grade = grades[‘Michael’]

except KeyError:

grade = -1

print(“Student not found”)


Here, we catch the KeyError exception in the except block and set the grade to -1 to indicate that the student was not found in the dictionary. We also print an error message to inform the user that the student was not found.

Another approach to handling KeyError is by using the `get()` method of dictionaries. The `get()` method returns the value for a given key if it exists in the dictionary, or a default value if the key is not found.

For example:


>>> grade = grades.get(‘Michael’, -1)


Here, we get the grade for a student named ‘Michael’, but if the student is not found in the dictionary, the method returns -1 as the default value. Finally, we can also use the `in` operator to check if a key exists in a dictionary before accessing it.

This approach is useful when we want to handle the KeyError exception manually. For example:


if ‘Michael’ in grades:

grade = grades[‘Michael’]


grade = -1

print(“Student not found”)


Here, we first check if the key ‘Michael’ exists in the dictionary using the `in` operator.

If it exists, we get the grade using the key. If not, we handle the exception manually by setting the grade to -1 and printing an error message.

In conclusion, understanding sets and handling the KeyError exception are essential concepts in Python. Sets provide a simple way to manage unique collections of elements, while handling KeyError exceptions is necessary to ensure that our programs behave as expected and do not terminate unexpectedly.

Knowing how to handle these exceptions using try-except blocks, `get()`, and `in` operators can help us write more reliable and robust Python programs. In summary, sets are a powerful and useful data structure in Python that allow developers to manage collections of unique elements.

They provide various methods to perform operations such as union, intersection, and difference, which are important for many programming tasks. Handling the KeyError exception is another essential concept that helps in ensuring that programs behave as intended and do not terminate unexpectedly.

By learning how to handle KeyError exceptions and use sets efficiently, developers can write more reliable and robust Python programs. Remember to use try-except blocks, the `get()` method, and `in` operators to handle exceptions and improve program reliability.

Understanding these concepts and implementing them in your code can make a significant difference in the quality of your Python projects.