为什么在python中使用星号扩展元组时使用逗号? [英] Why is comma used while extending tuple by using asterisk in python?

问题描述

在下面的代码中，如果我不使用逗号，那么只会打印一个 0，而如果我使用逗号，则 0 会打印五次，为什么?这与元组的不可变特性有关吗?

In the below code if I don't use comma then only one 0 gets printed while if I use comma 0 gets printed five times, why? Is it something to do with the immutable trait of the tuple?

 food = (0,) * 5  # comma used
 print (*food)

输出:0 0 0 0 0

Output: 0 0 0 0 0

 food = (0) * 5  # comma not used
 print (*food)

输出:0

推荐答案

这是一个语法问题.定义元组的不是括号，而是逗号的存在:

It's a syntax thing. What defines the tuple is not the parenthesis, but the presence of the comma:

• 围绕单个标量表达式的括号用于定义计算顺序:(1 + 2) * 3
• 由逗号分隔的表达式序列定义了一个元组:1, 2, 3.
  • 如果需要嵌入其他表达式，则可以将这个序列加括号:(1, 2, 3) * 5 是元组 (1,2,3) 重复五次".
  • Parenthesis around a single scalar expression are used to define order of evaluation: (1 + 2) * 3
  • A sequence of expressions separated by commas defines a tuple: 1, 2, 3.
    • This sequence can then be parenthesized if it needs to be embedded in some other expression: (1, 2, 3) * 5 is "the tuple (1,2,3) repeated five times".

    >>> type( (0, ) )
    tuple
    
    >>> type ( (0) )
    int
    
    

    所以 (0) * 5 是整数 0 乘以 5"，得到 0.在任何时候都没有涉及元组，因为您使用的语法没有定义元组.

    So (0) * 5 is "the integer 0 multiplied by 5", giving you 0. There's no tuple involved at any point because the syntax you used does not define a tuple.

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