是否有标准化的方法可以在Python中交换两个变量？

本文翻译自：Is there a standardized method to swap two variables in Python?

In Python, I've seen two variable values swapped using this syntax: 在Python中，我已经看到使用此语法交换了两个变量值：

left, right = right, left

Is this considered the standard way to swap two variable values or is there some other means by which two variables are by convention most usually swapped? 这是否被认为是交换两个变量值的标准方法，或者是否有其他一些方式可以按照惯例最通常地交换两个变量？

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#1楼

参考：https://stackoom.com/question/10Fa0/是否有标准化的方法可以在Python中交换两个变量

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#2楼

这是交换两个变量的标准方法，是的。

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#3楼

Python evaluates expressions from left to right. Python从左到右计算表达式。 Notice that while evaluating an assignment, the right-hand side is evaluated before the left-hand side. 请注意，在评估分配时，右侧的评估先于左侧。

http://docs.python.org/3/reference/expressions.html#evaluation-order http://docs.python.org/3/reference/expressions.html#evaluation-order

That means the following for the expression a,b = b,a : 这意味着表达式a,b = b,a ：

• the right-hand side b,a is evaluated, that is to say a tuple of two elements is created in the memory. 右边b,a被求值，也就是说在内存中创建了两个元素的元组。 The two element are the objects designated by the identifiers b and a , that were existing before the instruction is encoutered during an execution of program 这两个元素是由标识符b和a指定的对象，它们在程序执行期间对指令进行加密之前就已存在
• just after the creation of this tuple, no assignement of this tuple object have still been made, but it doesn't matter, Python internally knows where it is 创建此元组后，仍未分配该元组对象，但这没关系，Python内部知道它在哪里
• then, the left-hand side is evaluated, that is to say the tuple is assigned to the left-hand side 然后，评估左侧，即将元组分配给左侧
• as the left-hand side is composed of two identifiers, the tuple is unpacked in order that the first identifier a be assigned to the first element of the tuple (which is the object that was formely b before the swap because it had name b ) 因为左侧由两个标识符组成，所以对元组进行解压缩，以便将第一个标识符a分配给元组的第一个元素（这是交换之前为b的对象，因为它的名称为b ）
  and the second identifier b is assigned to the second element of the tuple (which is the object that was formerly a before the swap because its identifiers was a ) 并且第二个标识符b分配给元组的第二个元素（这是交换之前的a对象，因为其标识符为a ）

This mechanism has effectively swapped the objects assigned to the identifiers a and b 该机制有效地交换了分配给标识符a和b的对象

So, to answer your question: YES, it's the standard way to swap two identifiers on two objects. 因此，回答您的问题：是的，这是在两个对象上交换两个标识符的标准方法。
By the way, the objects are not variables, they are objects. 顺便说一下，对象不是变量，而是对象。

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#4楼

I know three ways to swap variables, but a, b = b, a is the simplest. 我知道三种交换变量的方法，但是a, b = b, a是最简单的。 There is 有

XOR (for integers) XOR（整数）

x = x ^ y
y = y ^ x
x = x ^ y

Or concisely, 或简而言之，

x ^= y
y ^= x
x ^= y

Temporary variable 临时变量

w = x
x = y
y = w
del w

Tuple swap 元组交换

x, y = y, x

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#5楼

I would not say it is a standard way to swap because it will cause some unexpected errors. 我不会说这是一种标准的交换方式，因为它将导致一些意外错误。

nums[i], nums[nums[i] - 1] = nums[nums[i] - 1], nums[i]

nums[i] will be modified first and then affect the second variable nums[nums[i] - 1] . nums[i]将首先被修改，然后影响第二个变量nums[nums[i] - 1] 。

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#6楼

Does not work for multidimensional arrays, because references are used here. 不适用于多维数组，因为此处使用了引用。

import numpy as np

# swaps
data = np.random.random(2)
print(data)
data[0], data[1] = data[1], data[0]
print(data)

# does not swap
data = np.random.random((2, 2))
print(data)
data[0], data[1] = data[1], data[0]
print(data)

See also Swap slices of Numpy arrays 另请参见交换Numpy数组的切片