What do square brackets enclosed in normal brackets do?

Question

For example in the computer variable, what purpose do the square brackets enclosed by the normal brackets server? I am new to python and confused about this. Thanks in advance!

import random

def play():
    user = input(" 'r' for rock, 'p' for paper, 's' for scissors: ")
    computer = random.choice(['r', 'p', 's'])

    if user == computer:
        return "tie"

That is just passing a list of three letters as a parameter to the `random.choice` function. The function chooses one and returns it. It is just like `func(x)`, except that `x` is a literal list. — Tim Roberts, Oct 22 '21 at 04:11
Square brackets represent a [`list`](https://docs.python.org/3/library/stdtypes.html#list) — President James K. Polk, Oct 22 '21 at 04:11

score 1 · Answer 1 · answered Oct 22 '21 at 04:16

whenever you use squared brackets you are defining a list (an array)

when you call a function (like random.choice ) need to use () to pass arguments

so in this case you are calling a function over a list the equivalen should be:

def play():
    user = input(" 'r' for rock, 'p' for paper, 's' for scissors: ")
    myList = ['r','p','s']
    random.choice(myList)
     if user == computer:
         return "tie"

this is a paper scissor rock game where the only response is to tie. the random.choice function select one element from an input List

Mohit Reddy · Answer 2 · 2021-10-22T04:25:56.857

1

The square brackets are actually a very simple term in python known as a list.

The code above could also translate to:

import random #Import random module

userinput = input(" 'r' for rock, 'p' for paper, 's' for scissors: ") #ask user what they want to input
choicelist = ['r', 'p', 's'] #List of options
computer = random.choice(choicelist) #pick a random option from list

if user == computer: #checking if they are both the same
    print("tie") #return tie if equal (Also this was a return which only works in functions, but i removed the function because it was not needed)

Please comment if you have any more questions!

edited Oct 22 '21 at 04:25

answered Oct 22 '21 at 04:20

Mohit Reddy

133
8

You are using `random.choice()`. I think you meant to pass the list as an argument to the fnction here? – rv.kvetch Oct 22 '21 at 04:23
1

Oh yea, i forgot to add it after I modified it. Whoops! – Mohit Reddy Oct 22 '21 at 04:25

tripleee · Answer 3 · 2021-10-22T04:28:19.127

function(a) means, call the function function with the argument a.

function([a]) means, call the function with the list [a] as its argument. Equivalently, you could write function(list(a))

Both characters have other uses; round parentheses can be used to group expressions, like in mathematics, which in Python also gets used to indicate a tuple. So,

function((a,)) means, call the function with the tuple (a,) as the argument. The comma is necessary to make it into a tuple; just (a) is merely the mathematical grouping we mentioned before, saying evaluate a before ... nothing. Equivalently, you could write function(tuple(a))

Square brackets are also used in indexing, so listvar[a] means the a:th element of the list variable listvar, and dictvar[a] means get the value for the key a from the dictionary dictvar.

For lists, the notation actually allows you to pull out sublists, called slices, in various ways, like listvar[:-a] or listvar[::]. This is complex enough that I'll defer the explanation of it to a separate question: Understanding slice notation

Square brackets are also used for various matrix notations in Numpy and Pandas, but that's not part of the Python core.

What do square brackets enclosed in normal brackets do?

3 Answers3