Python Developer Interview Questions India 2026

Tip: Lists are mutable, tuples are immutable. Tuples are faster and can be used as dictionary keys. Use tuples for fixed collections (coordinates, RGB), lists for data that changes.

Tip: The GIL is a mutex that prevents multiple native threads from executing Python bytecode simultaneously, so threads cannot achieve true CPU parallelism in CPython. Workaround: use multiprocessing for CPU-bound tasks, asyncio for I/O-bound tasks.

Tip: A decorator is a function that wraps another function to add behaviour without modifying it. Pattern: `def log(func): def wrapper(*args, **kwargs): print(func.__name__); return func(*args, **kwargs); return wrapper`. Use `functools.wraps` to preserve metadata.

Tip: Generators use `yield` and are lazy — they produce one value at a time, keeping only the current state in memory. A function returning a list loads all values at once. Use generators for large datasets, infinite sequences, or pipelines.

Tip: `@staticmethod` takes no implicit first argument — just a regular function namespaced in a class. `@classmethod` takes `cls` as first arg — it can access class state and is used for factory methods. Instance method takes `self` and can access both instance and class.

Tip: Django ORM maps model classes to DB tables. N+1: querying related objects in a loop triggers one query per object. Fix with `select_related()` for ForeignKey (JOIN) or `prefetch_related()` for ManyToMany. Always check the Django debug toolbar query count.

Tip: A virtual environment isolates project dependencies so two projects can use different versions of the same package without conflict. Create with `python -m venv .venv`, activate, then `pip install`. Always commit `requirements.txt` or `pyproject.toml`.

Tip: Quantify impact: "reduced report generation from 4 hours to 10 minutes." Mention libraries used, edge cases you handled, and how you tested it. Avoid generic "I built a CRUD app" — show problem-solving depth.

Tip: Profile first — never guess. Use `cProfile` or `py-spy` for CPU bottlenecks, Django debug toolbar for query issues. Common culprits: slow DB queries (missing index), serialisation overhead, or external API calls. Measure before and after any fix.

Tip: `*args` collects extra positional arguments as a tuple. `**kwargs` collects extra keyword arguments as a dict. Use when building wrappers/decorators or flexible APIs where the caller may pass an unknown number of arguments.

Tip: Shallow copy creates a new container but nested objects are still shared references. Deep copy recursively copies all nested objects. Shallow copy trap: mutating a nested list in the copy also changes the original.

Tip: Django: full-featured, admin panel, ORM, auth — best for data-heavy CRUD apps. Flask: lightweight, minimal, great for small APIs or prototypes. FastAPI: async-first, auto-generated OpenAPI docs, Pydantic validation — best for high-performance ML or data APIs.