将 * (splat) 运算符与 print 一起使用 [英] using the * (splat) operator with print

问题描述

我经常使用 Python 的 print 语句来显示数据.是的，我知道 '%s %d' % ('abc', 123) 方法和 '{} {}'.format('abc', 123) 方法，以及 ' '.join(('abc', str(123))) 方法.我还知道 splat 运算符 (*) 可用于将可迭代对象扩展为函数参数.但是，我似乎无法使用 print 语句来做到这一点.使用列表:

<预><代码>>>>l = [1, 2, 3]>>>升[1, 2, 3]>>>打印 l[1, 2, 3]>>>'{} {} {}'.format(*l)'1 2 3'>>>打印 *l文件<stdin>"，第 1 行打印 *l^语法错误:无效语法

使用元组:

<预><代码>>>>t = (4, 5, 6)>>>吨(4, 5, 6)>>>打印 t(4, 5, 6)>>>%d %d %d"%t'4 5 6'>>>'{} {} {}'.format(*t)'4 5 6'>>>打印 *t文件<stdin>"，第 1 行打印 *t^语法错误:无效语法

我错过了什么吗?这根本不可能吗?print 后面到底是什么东西?文档 说用逗号分隔的表达式列表遵循 print 关键字，但我猜这与列表数据类型不同.我在 SO 和网络上做了很多挖掘，但没有找到明确的解释.

我使用的是 Python 2.7.6.

解决方案

print 是 Python 2.x 中的语句，不支持 * 语法.您可以从 print 语法中看到这一点"noreferrer">文档:

<前>print_stmt ::= "print" ([表达式 ("," 表达式)* [","]]|">>" 表达式 [("," 表达式)+ [","]])

请注意在 print 关键字之后没有使用 * 的选项.

<小时>

但是，* 语法在函数调用内部被支持，而print 是 Python 3.x 中的一个函数.这意味着您可以从 __future__ 导入它:

from __future__ import print_function

然后使用:

print(*l)

演示:

<预><代码>>>># Python 2.x 解释器>>>从 __future__ 导入 print_function>>>l = [1, 2, 3]>>>打印(*l)1 2 3>>>

I often use Python's print statement to display data. Yes, I know about the '%s %d' % ('abc', 123) method, and the '{} {}'.format('abc', 123) method, and the ' '.join(('abc', str(123))) method. I also know that the splat operator (*) can be used to expand an iterable into function arguments. However, I can't seem to do that with the print statement. Using a list:

>>> l = [1, 2, 3]
>>> l
[1, 2, 3]
>>> print l
[1, 2, 3]
>>> '{} {} {}'.format(*l)
'1 2 3'
>>> print *l
  File "<stdin>", line 1
    print *l
          ^
SyntaxError: invalid syntax

Using a tuple:

>>> t = (4, 5, 6)
>>> t
(4, 5, 6)
>>> print t
(4, 5, 6)
>>> '%d %d %d' % t
'4 5 6'
>>> '{} {} {}'.format(*t)
'4 5 6'
>>> print *t
  File "<stdin>", line 1
    print *t
          ^
SyntaxError: invalid syntax

Am I missing something? Is this simply not possible? What exactly are the things that follow print? The documentation says that a comma-separated list of expressions follow the print keyword, but I am guessing this is not the same as a list data type. I did a lot of digging in SO and on the web and did not find a clear explanation for this.

I am using Python 2.7.6.

解决方案

print is a statement in Python 2.x and does not support the * syntax. You can see this from the grammar for print listed in the documentation:

print_stmt ::=  "print" ([expression ("," expression)* [","]]
                | ">>" expression [("," expression)+ [","]])

Notice how there is no option for using * after the print keyword.

---

However, the * syntax is supported inside function calls and it just so happens that print is a function in Python 3.x. This means that you could import it from __future__:

from __future__ import print_function

and then use:

print(*l)

Demo:

>>> # Python 2.x interpreter
>>> from __future__ import print_function
>>> l = [1, 2, 3]
>>> print(*l)
1 2 3
>>>

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