Python interview questions and answers

Each object has a refcount

Cycles delay reclamation until GC runs, which can retain large graphs longer than you expect.

A list holds every element at once.

__repr__ should be unambiguous and, if practical, look like a constructor call for debugging.

__enter__ runs at the start of a with block and its return value is bound to as.

__getitem__ implements indexing and slicing, and if it raises IndexError, for-loops can treat the object as a sequence.

groupby clusters consecutive items that share a key function's result.

chain concatenates iterables without building an intermediate list, useful when merging query results you already have as iterators.

yield produces iterator values and pauses a generator.

The loop schedules ready callbacks and coroutines, waits on sockets, and resumes them when I/O completes.

args collects extra positional arguments as a tuple.

A generator yields values lazily with yield instead of building a full list in memory.

Model talks to the database, View holds request logic, Template renders HTML.

ORM maps Python model classes to tables and builds SQL for you.

Good for light decoupled side effects

The Global Interpreter Lock allows only one thread to execute Python bytecode at a time in a process.

It memoizes pure functions with a size limit.

It locks rows inside a transaction to avoid race updates.

with guarantees cleanup via __enter__/__exit__ even on errors.

select_related joins forward FK/OneToOne in one query.