Python就地解压缩似乎无法按预期工作

Question

I've seen a lot of questions on here about using * before a tuple to expand it into something else, but it doesn't seem to work for me.

>>> l1 = (1, 2, 3)
>>> l2 = (0, l1, 4)
>>> l2   (0, (1, 2, 3), 4)
>>> l2 = (0, *l1, 4)
File "<stdin>", line 1  
    l2 = (0, *l1, 4)  
             ^   SyntaxError: invalid syntax 

As you can see. I can't get l1 to expand into l2 with the * operator...

Note: This is python2.7

Answer 1

In-place unpacking has been introduced in python 3.5 and it works in later versions not older ones.

# Python 3.5
In [39]: (3, *l1, 4)
Out[39]: (3, 1, 2, 3, 4)

In older versions you can use + operator or itertools.chain function for longer iterables:

In [40]: (3,) + l1 + (4,)
Out[40]: (3, 1, 2, 3, 4)

In [41]: from itertools import chain

In [45]: tuple(chain((3,), l1, (4,)))
Out[45]: (3, 1, 2, 3, 4)

Answer 2

First of all, those aren't lists , they're tuples . They are similar but not the same thing.

Second, the *arg syntax is called argument expansion , and it only works for function arguments

def func(a, b):
    return a + b

my_list = [1, 2]
func(*my_list)

EDIT:

Apparently, in-place unpacking was added in python 3.5, but for the overwhelming majority of python installations you encounter, my answer still holds true. Perhaps in 2020 when Python 2 stops being supported this will change, but for now and the immediate future, expect the above to be true.