Python what is '*' used for

Question

So here's my code:

user_input = input('What number would you like to convert?: ')
binary = []
num = int(user_input)
while num != 0:
    remainder = num % 2
    num = (num - remainder)  / 2
    binary.append(int(remainder))
print(user_input, 'in binary is: ', end='')
print(*reversed(binary), sep='')

Why do i have to have the '*' before printing out the array? i looked everywhere and couldn't find what it does and what its used for.

Thanks in advance, Rob

tckmn · Accepted Answer · 2014-12-20T18:06:10.223

0

This is called the "splat" operator. For more information on it, see the Python documentation on it.

What it's basically doing is this:

print(reversed(binary)[0], reversed(binary)[1], ..., sep='')

Essentially, it uses the array elements as arguments instead of passing the array as a single argument itself.

>>> lst = [1, 2, 3]
>>> print(lst)  # equivalent to `print([1, 2, 3])'
[1, 2, 3]
>>> print(*lst) # equivalent to `print(1, 2, 3)'
1 2 3
>>> print(reversed(lst))
<list_reverseiterator object at 0x7f4863ae4a20>
>>> print(*reversed(lst))
3 2 1

edited Dec 20 '14 at 18:06

answered Dec 20 '14 at 17:51

tckmn

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Is splat operator available in python 2.7? – Shahriar Dec 20 '14 at 17:54
@AerofoilKite Yes, it has existed since the very first version of Python as far as I know. – tckmn Dec 20 '14 at 17:54
yes, even 2.6, and 3 as well. – micromoses Dec 20 '14 at 17:55
@Doorknob冰, its giving me [SyntaxError: invalid syntax] indicating '*' – Shahriar Dec 20 '14 at 17:56
@AerofoilKite Are you running the last line of code posted in the question? If so, the problem is that `print` is not a function in Python 2. – tckmn Dec 20 '14 at 17:57
I thought you could print tables like print(numbers), but essentially using the splat operator is referring to the elements of the table? – user3124289 Dec 20 '14 at 17:57
print *reversed(binary) in python 2.7 – Shahriar Dec 20 '14 at 17:58
@user3124289 Here, I've added a simpler example in my answer to help explain. – tckmn Dec 20 '14 at 17:59
@AerofoilKite Yes, that doesn't work because `print` is not a function in Python 2. You could try `from __future__ import print_function`, after which it should work. – tckmn Dec 20 '14 at 17:59
print(*lst) this is giving error.. What is the equivalent code for 2.7 using splat – Shahriar Dec 20 '14 at 18:00
1

Oh I see. so if I do `print([1, 2, 3])` it prints [1, 2, 3], but if i do `print(*[1, 2, 3])` it prints 1 2 3 – user3124289 Dec 20 '14 at 18:00
@user3124289 Yes, that is correct. In the first, case, you are passing one argument (the list), but in the second, you are passing three arguments (each element of the list). – tckmn Dec 20 '14 at 18:01
@Doorknob冰, what do you mean by print is not a function in Python 2. print lst -> this is working fine – Shahriar Dec 20 '14 at 18:01
@AerofoilKite `print` is a **statement**, not a **function**, in Python 2. – tckmn Dec 20 '14 at 18:02
reversed returns an iterator, so `print(reversed(binary))` prints ``. Splashing it prints the binary digits. – miraculixx Dec 20 '14 at 18:04

Python what is '*' used for

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