Brackets or parentheses

Question

I find it difficult to know when to use brackets or parentheses. E.g. numbers = list(range(3, 8))
Here I expect brackets, but it's not.

Answer 1

Brackets -- "[]" -- are used to get an item out of a list or dictionary. Here are some examples:

>>> a = [1,2,3,4]
>>> a[2]
3
>>> b = { 'age': 32, 'iq': 140, 'weight': 125 }
>>> b['iq']
140

Brackets may also be used to create a list comprehension. For example, here's one way to create a list of numeric strings containing the numbers from 1 to 10.

>>> [str(_) for _ in range(1, 11)]
['1', '2', '3', '4', '5', '6', '7', '8', '9', '10']

Parentheses are used when we're calling a function. In the example in your question -- list(range(3,8)) -- list and range are functions.

Parentheses are also used to group parts of an expression. For example,

>>> q = 3 * (2 + 5)
>>> q
21
>>> p = 3 * 2 + 5
>>> p
11

Answer 2

Thank you very much for your very clear explanation. It makes sense now. I don't have to doubt anymore.

Answer 3

() - tuples, functions, math

[] - lists, splicing

i.e
(1,2)[0] == 1,
[1,2,3,4][1] == 1,
{1: 1,2:2,3:3}[2] == 2

{} - maps/dictionaries depending on what you call them