Python — Interview Refresher

Quick brush-up. Your Java brain already knows the concepts — this maps them to Python + the gotchas interviewers probe.

Language essentials

Key data structures?

list (mutable, ordered), tuple (immutable, ordered), dict (hash map), set (unique). Comprehensions: [x*2 for x in xs if x>0].

Mutable vs immutable?

Immutable: int, str, tuple, frozenset. Mutable: list, dict, set. Matters for default args and shared references.

Mutable default argument trap (classic)

def f(x, acc=[]): — the list is created once and shared across calls → surprise state. Fix: def f(x, acc=None): acc = acc or [].

is vs ==?

== compares values; is compares identity (same object). Like Java’s equals vs ==.

Shallow vs deep copy?

copy.copy (shallow — nested refs shared) vs copy.deepcopy (fully independent).

The GIL (they ask this for “Python concurrency”)

What is the GIL and why does it matter?

Global Interpreter Lock — only one thread executes Python bytecode at a time. So Python threads DON’T give true CPU parallelism. Use threads for I/O-bound work (they release the GIL while waiting), use multiprocessing for CPU-bound (separate processes, separate GILs). (Note: Python 3.13+ has an experimental no-GIL build.)

Pythonic / OO

Decorators?

A function that wraps another to add behavior (@app.route, @staticmethod). Same idea as Java annotations + AOP, but plain functions.

Generators / yield?

Lazy iterators — produce values on demand, memory-efficient. yield pauses and resumes.

List comprehension vs generator expression?

[...] builds the whole list in memory; (...) is a lazy generator (streams one at a time).

args/kwargs?

*args = variable positional args (tuple); **kwargs = variable keyword args (dict).

Your honesty framing

Positioning Python (you're Java-core)

“My core is Java; I’ve used Python across NLP, chatbots, and Flask services, and I ramp fast. I’m comfortable with the syntax, comprehensions, and the concurrency model — the GIL, threads for I/O vs multiprocessing for CPU.” True + confident.

Drill cards

GIL — what and impact?::Global Interpreter Lock: one thread runs Python bytecode at a time. Threads for I/O-bound, multiprocessing for CPU-bound.
is vs ?:: compares values; is compares identity (same object).
Mutable default arg trap?::Default list/dict is created once and shared across calls; use None and create inside.
Generator vs list comprehension?::Generator (parentheses) is lazy/streaming/memory-light; list comp builds it all in memory.
Mutable vs immutable types?::Immutable: int, str, tuple, frozenset. Mutable: list, dict, set.