使用序列解包的ipython怪异行为

Question

I have a weird behavior with sequence unpacking in ipython

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

This syntax ( PEP 3132 - Extended Iterable Unpacking ) was introduced in Python 3.0. Check you python version.

In Python 3.3:

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

In Python 2.7, it raises 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]