普通括号中的方括号有什么作用？

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"

Answer 1

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

Answer 2

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!

Answer 3

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.