Top 17 Python Interview Questions Every Backend Engineer Should Master

1. What does the pass statement do in Python?

The pass statement does nothing; it serves as a placeholder in code where a statement is syntactically required but no action is needed.

2. How does Python perform type conversion?

Python offers built‑in functions such as int() to convert values from one type to another, e.g., turning a numeric string into an integer, otherwise raising an error.

3. How does Python manage memory?

Python uses a memory‑pool mechanism called Pymalloc to allocate and free small memory blocks efficiently.

4. Difference between dict.items() and dict.iteritems() ?

items()

returns a list of key‑value pairs (order not guaranteed), while iteritems() returns an iterator over those pairs.

5. What is a lambda function and its benefits?

A lambda expression creates an anonymous, single‑line function useful when a full function definition is unnecessary. It can accept any number of arguments but contains only one expression, returning its value.

6. Differences between os and sys modules and common methods

os : Provides a portable way to use operating‑system‑dependent functionality.

sys : Gives access to interpreter‑maintained variables and functions that interact closely with the Python runtime.

7. How to copy objects in Python? Difference between copy and deepcopy

copy()

duplicates the object itself without copying objects it references. deepcopy() recursively copies the object and all objects it references.

8. Difference between os.path and sys.path

os.path

is a module offering functions for pathname manipulation. sys.path is a list of directory strings that Python searches for modules.

9. Difference between re.match and re.search

match()

checks for a match only at the beginning of a string, while search() scans the entire string for a match.

10. Generators vs. functions

Functions use return to output a value and terminate, whereas generators use yield to produce a value and pause, resuming later from the same point.

11. Relationship between WSGI and FastCGI

Both are interfaces for connecting web servers to applications. CGI is a generic protocol; FastCGI is a long‑living, language‑agnostic extension that keeps processes in memory for better performance. WSGI (Web Server Gateway Interface) is the Python‑specific standard that serves a similar purpose.

12. Django vs. Tornado

Django is a high‑level, batteries‑included web framework emphasizing rapid development, MVC design, and ORM.

Tornado is a non‑blocking, scalable web server and framework designed for handling thousands of simultaneous connections, ideal for real‑time services.

13. Using django-debug-toolbar

Add 'debug_toolbar.middleware.DebugToolbarMiddleware' to MIDDLEWARE_CLASSES in settings.py to enable the toolbar.

14. Configuring Redis cache in Django

Install the Redis‑for‑Django package, then configure the cache backend in settings.py. Example configuration shown in the accompanying image.

15. Running Django unit tests

Django tests use Python’s unittest framework. Define test classes inheriting from django.test.TestCase. Run tests with commands such as:

$ python manage.py test

$ python manage.py test animals.tests

$ python manage.py test animals.tests.AnimalTestCase

$ python manage.py testanimals.tests.AnimalTestCase.test_animals_can_speak

$ python manage.py test --pattern="tests_*.py"

$ python -Wall manage.py test

16. Overview of the HTTP protocol

HTTP is an application‑layer, stateless, request/response protocol designed for fast, simple communication. Key characteristics include client/server model, simplicity, flexibility (any MIME type), connectionless nature, and statelessness.

17. Common HTTP request headers and status codes

Headers such as Accept, Accept-Charset, Accept-Language, Accept-Encoding, Cache-Control, Connection, Content-Type, and Cookie control content negotiation and connection behavior.

Status code classes: 1xx (informational), 2xx (success), 3xx (redirection), 4xx (client error), 5xx (server error). Common codes include 200 OK, 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 500 Internal Server Error, 503 Service Unavailable.