python - ipython 序列解包的奇怪行为

Question

我在 ipython 中进行序列解包时有一个奇怪的行为

In [12]: items = [1, 10, 7, 4, 5, 9]

In [13]: head, *tail = items
  File "<ipython-input-13-34256df22cca>", line 1
    head, *tail = items
          ^
SyntaxError: invalid syntax

Answer 1

此语法 ( PEP 3132 - Extended Iterable Unpacking ) 是在 Python 3.0 中引入的。检查你的Python版本。

在 Python 3.3 中:

>>> items = [1, 10, 7, 4, 5, 9]
>>> head, *tail = items
>>> head
1
>>> tail
[10, 7, 4, 5, 9]

在 Python 2.7 中，它会引发 SyntaxError:

>>> items = [1, 10, 7, 4, 5, 9]
>>> head, *tail = items
  File "<stdin>", line 1
    head, *tail = items
          ^
SyntaxError: invalid syntax
>>> head, tail = items[0], items[1:] # workaround
>>> head
1
>>> tail
[10, 7, 4, 5, 9]