Question 1

What is the difference between mutable and immutable types?

Accepted Answer

Mutable objects change in place, immutable ones create a new object, and only immutable (hashable) objects can be dict keys.

Question 2

List vs tuple vs set vs dict: when do you use each?

Accepted Answer

I'd use a set when I only care about membership or uniqueness, because lookups are constant time on average.

Question 3

Shallow copy vs deep copy?

Accepted Answer

Shallow copies share nested objects, so for nested data I use copy.deepcopy.

Question 4

What is wrong with def add(x, items=[])?

Accepted Answer

Default arguments are evaluated once, so I use None as the default and build the list inside the function.

Question 5

What is the difference between == and is?

Accepted Answer

I use == for values and is only for identity checks like x is None.

Question 6

What are *args and **kwargs?

Accepted Answer

*args gathers extra positional arguments into a tuple, and **kwargs gathers extra keyword arguments into a dict.

Question 7

List comprehension vs generator: what is the difference?

Accepted Answer

For big or streaming data I use a generator so I don't hold everything in memory.

Question 8

What is a decorator?

Accepted Answer

A decorator wraps a function to add behaviour without changing its code, and @name is shorthand for f = name(f).

Question 9

What is the GIL, and what does it mean for threads?

Accepted Answer

Because of the GIL I use threads or asyncio for I/O waits and multiprocessing for CPU-bound work.

Question 10

How do try, except, else and finally work together?

Accepted Answer

I catch specific exceptions, keep the success path in else, and put cleanup in finally or a with block.

Python, in 10 cards

What is the difference between mutable and immutable types?