Question 1

What is the difference between positional-only and keyword-only parameters?

Accepted Answer

Parameters before the / marker cannot be passed by name (positional-only), and parameters after * must be passed by name (keyword-only).

Question 2

Why is a list as a default parameter value a problem?

Accepted Answer

Because the default value is evaluated only once, when the function is defined, so all calls share the same list and data accumulates in it.

Question 3

How do *args and **kwargs work?

Accepted Answer

*args collects extra positional arguments into a tuple and **kwargs collects extra keyword arguments into a dict; * and ** can also be used at call time to unpack values.

Question 4

What is a closure, and what is the late-binding problem inside loops?

Accepted Answer

A closure is an inner function that keeps a reference to variables of the enclosing scope, but the variable's value is read at call time, not creation time, so all functions created in a loop see the loop variable's last value.

Question 5

How do you write a decorator that preserves the original function's metadata?

Accepted Answer

Write a function that receives the original function and returns a wrapper, and apply functools.wraps to the wrapper to copy __name__, __doc__, __module__ and __wrapped__.

Question 6

Explain the LEGB rule for name resolution.

Accepted Answer

Python looks up a name in this order: Local (the current function), Enclosing (the surrounding functions), Global (the module), then Builtins.

Question 7

When should you use lambda and when def?

Accepted Answer

Use lambda for a small expression passed directly as an argument (such as key in sorted), and use def for any logic that needs a name, more than one expression, documentation or tests.

Question 8

What is functools.partial for?

Accepted Answer

It creates a new callable that fixes some arguments of an existing function, which helps when passing a callback that needs fixed context.

Question 9

What are the limits of recursion in Python, and when should you choose a loop?

Accepted Answer

Every call uses a stack frame, the default recursion depth limit is about 1000, and Python does not optimize tail calls, so a loop or an explicit stack suits deep data better.

Question 10

What does it mean that functions in Python are first-class objects?

Accepted Answer

A function can be assigned to a variable, passed as an argument, returned from another function, and stored in data structures like any other object.