Commas in python?

Question

I want to understand function from random.py: Why the last line looks so?

def shuffle(self, x, random=None, int=int):
    randbelow = self._randbelow
    for i in reversed(range(1, len(x))):
        # pick an element in x[:i+1] with which to exchange x[i]
        j = randbelow(i+1) if random is None else int(random() * (i+1))
        x[i], x[j] = x[j], x[i]

Why it's not single:

x[j] = x[j]

Sorry it seemed to me as x[j] = x[i], i need some sleep=) – Ivan Borshchov Mar 30 '14 at 21:27 — Ivan Borshchov, Mar 30 '14 at 21:27

score 4 · Accepted Answer · edited May 23 '17 at 12:28

4

a, b = b, a is idiomatic Python for "swap a and b".

x[i], x[j] = x[j], x[i]  # Swaps x[i] and x[j]

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edited May 23 '17 at 12:28

Community

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answered Mar 30 '14 at 21:27

johnsyweb

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score 3 · Answer 2 · answered Mar 30 '14 at 21:24

3

This line swaps element j and element i of x.

answered Mar 30 '14 at 21:24

foobarbecue

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valentine · Answer 3 · 2014-03-30T21:30:37.787

2

this is shorthand for:

x[j]=x[i]
x[i]=x[j]

Notice though, if you were to do it in two lines, the value of x[j] would be overwritten by the new value of x[i]. By doing it in one line the way the authors did, the new value of x[j] will be set to the old value of x[i] and the new value of x[i] will be set to the old value of x[j].

edited Mar 30 '14 at 21:30

answered Mar 30 '14 at 21:24

valentine

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Commas in python?

3 Answers3

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