100+ Python and Django Developer Interview Questions and Answers

GIL is a mutex that protects access to Python objects, preventing multiple threads from executing Python bytecodes simultaneously.

• GIL is a global lock that allows only one thread to execute Python bytecode at a time.

• It is necessary because CPython's memory management is not thread-safe.

• GIL can limit the performance of multi-threaded Python programs, especially on multi-core systems.

• However, it does not prevent multi-threading entirely, as I/O-bound tasks can still benefit fro...read more

Media queries are CSS rules that allow for different styles to be applied based on the characteristics of the device displaying the webpage.

• Media queries are used in responsive web design to make websites adapt to different screen sizes and resolutions.

• They are written using the @media rule in CSS.

• Media queries can target various features such as screen width, height, orientation, and resolution.

• Example: @media only screen and (max-width: 600px) { /* styles for screens up to ...read more

Django ORM is used to interact with the database in a more Pythonic way, allowing developers to work with database tables as Python objects.

• Django ORM abstracts away the complexities of SQL queries, making it easier for developers to interact with the database.

• It provides an object-oriented interface to interact with the database, allowing developers to define models and perform CRUD operations.

• Django ORM automatically handles database transactions, migrations, and relationsh...read more

Use the print() function in Python to display 'Hello World'.

• Use the print() function followed by the string 'Hello World'

• Enclose the string in single or double quotes

• Example: print('Hello World')

Yes, the Global Interpreter Lock (GIL) in Python ensures only one thread can execute Python bytecode at a time, limiting the efficiency of multi-threading.

• GIL is a mutex that protects access to Python objects, preventing multiple threads from executing Python bytecodes simultaneously.

• This means that even on multi-core systems, Python threads cannot fully utilize all available CPU cores for parallel processing.

• However, GIL does not prevent multi-threading for I/O-bound tasks o...read more

Django follows Model-View-Controller (MVC) architectural pattern.

• Django has three core components: Model, View, and Template.

• Model: Defines the database schema and handles data manipulation.

• View: Handles user requests and returns responses.

• Template: Renders the HTML pages.

• Django also has middleware, which is a way to add extra functionality to the request/response process.

• Django's URL routing maps URLs to views.

• Django's ORM (Object-Relational Mapping) maps database tables to ...read more

Race condition occurs when multiple threads/processes access and modify shared data simultaneously.

• It can lead to unpredictable behavior and data corruption.

• Django provides thread-safe mechanisms like database transactions and caching to prevent race conditions.

• Example: If two users try to update the same record in the database at the same time, it can result in inconsistent data.

• Another example is when multiple requests are made to update the same cache key simultaneously, l...read more

Both Django and Flask are popular Python web frameworks, but Django is better for larger, more complex projects while Flask is better for smaller, simpler projects.

• Django is a full-featured framework with built-in tools for authentication, routing, and database management, making it ideal for large-scale applications.

• Flask is a micro-framework that is lightweight and flexible, making it a good choice for smaller projects or prototypes.

• Django follows the 'batteries included' p...read more

Types of Serializers in Django include ModelSerializer, Serializer, and HyperlinkedModelSerializer.

• ModelSerializer: Used to serialize Django model instances.

• Serializer: Generic serializer class for custom data serialization.

• HyperlinkedModelSerializer: Includes hyperlinks to related resources in the serialized data.

Middleware is a framework of hooks into Django's request/response processing. It is used to perform actions before and after the view is called.

• Middleware is a Python class that defines hooks that can alter the request/response cycle.

• It can be used for authentication, logging, error handling, etc.

• Middleware classes are defined in settings.py and executed in the order they are listed.

• Example: Django's AuthenticationMiddleware is a built-in middleware that handles user authenti...read more

Tuples are immutable sequences used to store multiple items in a single variable. They are commonly used for grouping related data.

• Tuples are created using parentheses () and can contain any type of data.

• They are immutable, meaning their values cannot be changed once assigned.

• Tuples are often used to return multiple values from a function.

• They can be used as keys in dictionaries since they are immutable.

• Tuples are more memory-efficient than lists.

• Example: person = ('John', 25...read more

Django is a high-level Python web framework that follows the model-view-controller architectural pattern.

• Django is a free and open-source framework.

• It is used for building web applications quickly and efficiently.

• Django follows the DRY (Don't Repeat Yourself) principle.

• It provides a robust set of tools and features for handling common web development tasks.

• Django uses the model-view-controller (MVC) architectural pattern.

• It includes an ORM (Object-Relational Mapping) for data...read more

To globally scale an application, consider using load balancing, caching, database sharding, and microservices architecture.

• Implement load balancing to distribute incoming traffic across multiple servers to prevent overload.

• Use caching to store frequently accessed data in memory for faster retrieval.

• Implement database sharding to horizontally partition data across multiple databases to improve performance.

• Consider using a microservices architecture to break down the applicati...read more

ORM stands for Object-Relational Mapping, a technique to map objects from an application to tables in a relational database.

• ORM allows developers to interact with a database using objects instead of SQL queries.

• It helps in abstracting the database interactions, making it easier to work with databases in an object-oriented way.

• ORM frameworks like Django ORM in Python provide tools to define models that represent database tables and perform CRUD operations.

• Example: In Django OR...read more

Django follows Model-View-Controller (MVC) architectural pattern.

• Django has a high-level architecture that follows the Model-View-Controller (MVC) architectural pattern.

• The Model layer represents the database schema and data access layer.

• The View layer is responsible for rendering the HTML content.

• The Controller layer handles the user requests and manages the flow of data between the Model and View layers.

• Django also includes a URL dispatcher, which maps URLs to views.

• Django'...read more

Method overloading is having multiple methods with the same name but different parameters. Method overriding is having a method in a subclass with the same name and parameters as in the superclass.

• Method overloading is used to provide different ways of calling the same method with different parameters.

• Method overriding is used to provide a specific implementation of a method in a subclass that is already defined in the superclass.

• Method overloading is resolved at compile-time...read more

NPFC stands for NumPy Financial Calculations, a library in Python for financial calculations.

• NPFC is a library in Python that provides functions for various financial calculations such as present value, future value, net present value, internal rate of return, etc.

• It is built on top of NumPy and provides a set of financial functions that are commonly used in finance and investment analysis.

• NPFC simplifies the process of performing complex financial calculations by providing r...read more

Python is a high-level, interpreted programming language known for its simplicity and readability.

• Python is widely used for web development, data analysis, artificial intelligence, scientific computing, and more.

• It emphasizes code readability and uses indentation to define code blocks.

• Python supports multiple programming paradigms, including procedural, object-oriented, and functional programming.

• It has a large standard library and a vibrant community that contributes to vari...read more

The task is to parse a JSON object and replace all numbers with the string 'number'.

• Use the json module in Python to parse the JSON object.

• Iterate through the JSON object and check the type of each value.

• If the value is a number, replace it with the string 'number'.

Binary search algorithm to find an element in a sorted array.

• Define a function that takes a sorted array and a target element as input.

• Initialize low and high pointers to the start and end of the array.

• While low pointer is less than or equal to high pointer, calculate mid pointer and compare target with element at mid.

• If target is found at mid, return mid index. If target is less than element at mid, update high pointer. If target is greater, update low pointer.

• Repeat until t...read more

Core python libraries are essential modules that come built-in with Python installation.

• Some core python libraries include 'os' for operating system interactions, 'sys' for system-specific parameters and functions, 'math' for mathematical functions, and 'datetime' for date and time manipulation.

• Other core libraries include 'random' for generating random numbers, 'json' for JSON encoding and decoding, 're' for regular expressions, and 'collections' for additional data structur...read more

A class is a blueprint for creating objects, while an object is an instance of a class. Classes define the properties and behaviors of objects.

• A class is a template for creating objects with similar properties and behaviors

• An object is an instance of a class, created using the class blueprint

• Classes can have attributes (variables) and methods (functions)

• Objects can interact with each other by calling methods on each other

• Example: Class 'Car' defines properties like 'color' an...read more

Method Resolution Order (MRO) is the order in which classes are searched for a method or attribute in Python.

• MRO is determined by the C3 linearization algorithm in Python.

• It follows a depth-first left-to-right traversal of the class hierarchy.

• MRO is important in multiple inheritance scenarios to resolve method conflicts.

• Example: class A: pass class B(A): pass class C(A): pass class D(B, C): pass

HTML is a markup language used for creating the structure of web pages, while CSS is a styling language used for designing the appearance of web pages.

• HTML stands for HyperText Markup Language and is used to create the structure of web pages.

• CSS stands for Cascading Style Sheets and is used to style the appearance of web pages.

• HTML uses tags to define elements like headings, paragraphs, images, links, etc.

• CSS is used to control the layout, colors, fonts, and other visual aspe...read more

CRUD stands for Create, Read, Update, and Delete - the four basic functions of persistent storage.

• Create - Adding new data to the database

• Read - Retrieving existing data from the database

• Update - Modifying existing data in the database

• Delete - Removing data from the database

• CRUD operations are commonly used in database management systems and web applications

Class method is bound to the class itself, while static method is not bound to any specific instance or class.

• Class method takes 'cls' as the first parameter, allowing access to class variables and methods.

• Static method does not take any special parameters and does not have access to class or instance variables.

• Class method can be called on both the class and instances of the class.

• Static method is mainly used for utility functions that do not require access to class or insta...read more

A decorator is a design pattern in Python that allows a user to add new functionality to an existing object or function.

• Decorators are denoted by the @ symbol followed by the name of the decorator function.

• They are used to modify the behavior of functions or classes without directly changing their source code.

• Decorators can be used for logging, timing, authentication, caching, and more.

• They can be applied to functions, methods, or classes.

• An example of a decorator is the @sta...read more

Python has several popular frameworks including Django, Flask, and Pyramid.

• Django is a high-level Python web framework that encourages rapid development and clean, pragmatic design.

• Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy.

• Pyramid is a lightweight Python web framework aimed at taking small web apps to large web apps.

Docker image is a template used to create containers, while a container is a running instance of an image.

• Docker image is read-only, while a container is a writable instance of an image.

• Multiple containers can be created from the same image, but each container is isolated from others.

• Containers can be started, stopped, moved, and deleted, while images are static and cannot be changed.

• Images are used to package an application and its dependencies, while containers are used to ...read more

To scale an app globally, I would utilize cloud services, implement caching mechanisms, optimize database queries, use content delivery networks, and employ load balancing.

• Utilize cloud services like AWS, Google Cloud, or Azure to easily scale resources based on demand

• Implement caching mechanisms such as Redis or Memcached to reduce server load and improve response times

• Optimize database queries by indexing frequently accessed data and using efficient query techniques

• Use cont...read more

Lambda expression for even numbers

• Use the lambda keyword to define the lambda function

• Use the modulo operator (%) to check if a number is even

• Return True if the number is even, else False

Lists are mutable, ordered collections of items, while tuples are immutable, ordered collections. Dictionaries are key-value pairs.

• Lists are denoted by square brackets [], tuples by parentheses (), and dictionaries by curly braces {}.

• Lists can be modified after creation, while tuples cannot be changed once created.

• Dictionaries store data in key-value pairs, allowing for quick lookups based on keys.

• Example: list = [1, 2, 3], tuple = (4, 5, 6), dict = {'key1': 'value1', 'key2':...read more

Access specifiers are keywords in programming languages that define the accessibility of classes, methods, and variables.

• Access specifiers control the visibility and accessibility of class members in object-oriented programming languages.

• Common access specifiers include public, private, and protected.

• Public members are accessible from outside the class, private members are only accessible within the class, and protected members are accessible within the class and its subclass...read more

Function annotations are a way to add metadata to function parameters and return values in Python.

• Function annotations are optional and do not have any impact on the function's behavior.

• Annotations are defined using a colon after the parameter name or return value, followed by the annotation expression.

• Annotations can be any valid Python expression, such as types, strings, or even functions.

• Annotations are stored in the function's __annotations__ attribute as a dictionary.

Signals in Django are used to allow decoupled applications to get notified when certain actions occur elsewhere in the application.

• Signals are used for sending notifications across different parts of a Django application.

• They allow decoupled applications to get notified when certain actions occur, such as when a model is saved.

• Signals are defined by creating a receiver function and connecting it to a signal using the @receiver decorator.

• Example: Sending an email notification ...read more

Shallow copy creates a new object but references the same memory addresses, while deep copy creates a new object with new memory addresses.

• Shallow copy only copies the top-level object, not nested objects.

• Deep copy creates copies of all nested objects as well.

• Changes to nested objects in a shallow copy will affect the original object, while changes in a deep copy will not.

SQL is a programming language used for managing and manipulating relational databases.

• SQL stands for Structured Query Language.

• It is used to communicate with databases to perform tasks such as querying data, updating data, and creating databases.

• Common SQL commands include SELECT, INSERT, UPDATE, DELETE.

• Example: SELECT * FROM table_name WHERE condition;

Sharding is a database partitioning technique to distribute data across multiple servers.

• Sharding helps improve scalability by distributing data across multiple servers.

• Each shard is a separate database that stores a subset of the data.

• Sharding can be based on different criteria like range-based, hash-based, or key-based sharding.

• Example: In a social media platform, user data can be sharded based on the user's geographical location.

Celery is a distributed task queue that allows you to run background jobs asynchronously in your Python web application.

• Celery is used to handle time-consuming tasks outside of the request-response cycle.

• It supports scheduling, retries, and prioritization of tasks.

• Celery can be integrated with various message brokers like RabbitMQ, Redis, and Amazon SQS.

• Example use cases include sending emails, processing images, and generating reports.

Use string manipulation to reverse an integer in Python.

• Convert the integer to a string

• Use string slicing to reverse the string

• Convert the reversed string back to an integer

Transactions in SQL are a way to ensure data integrity by grouping multiple SQL statements into a single unit of work.

• Transactions help maintain the ACID properties (Atomicity, Consistency, Isolation, Durability) of a database.

• They allow multiple SQL statements to be executed as a single unit, either all succeeding or all failing.

• Transactions can be started with BEGIN TRANSACTION, COMMIT to save changes, or ROLLBACK to undo changes.

• Example: transferring money from one account...read more

Rest Api is a way for applications to communicate over the internet using HTTP requests.

• Rest Api stands for Representational State Transfer Application Programming Interface.

• It allows different software applications to communicate with each other over the internet.

• Rest Api uses standard HTTP methods like GET, POST, PUT, DELETE to perform operations on resources.

• Rest Api responses are usually in JSON or XML format.

• Example: Using Rest Api to retrieve data from a database by sen...read more

DRF provides JSON, BrowsableAPI, TemplateHTML, and AdminRenderer classes for rendering responses.

• JSONRenderer: Renders data in JSON format.

• BrowsableAPIRenderer: Renders data in a browsable HTML format with forms for interacting with the API.

• TemplateHTMLRenderer: Renders data using a specified template in HTML format.

• AdminRenderer: Renders data in a format suitable for Django admin interface.

A regular expression is a sequence of characters that defines a search pattern.

• Regular expressions are used for pattern matching and searching in strings.

• They provide a concise and flexible way to search, extract, and manipulate text.

• Regular expressions can be used in various programming languages, including Python.

• They consist of metacharacters, literals, and special sequences.

• Examples of regular expressions include matching email addresses, phone numbers, or URLs.

Primary key is a unique identifier for each record in a database table.

• Primary key ensures that each record in a table is unique.

• It is used to establish relationships between tables.

• Primary key can be a single column or a combination of columns.

• It cannot have null values.

• Examples of primary keys are social security numbers, email addresses, and employee IDs.

Jinja templating is a popular template engine for Python web development, used in frameworks like Flask and Django.

• Jinja allows for dynamic content generation in HTML templates

• It uses double curly braces {{ }} for placeholders and control structures like loops and conditionals

• Jinja templates can be extended and included for reusability

• Example: {{ variable }} or {% for item in list %}

Decorators in Python are functions that modify the behavior of other functions or methods.

• Decorators are used to add functionality to existing functions without modifying their code.

• Types of decorators in Python include function decorators, class decorators, and method decorators.

• Example: @staticmethod and @classmethod are built-in decorators in Python.