Is there a standardized method to swap two variables in Python

Question

In Python  I ve seen two variable values swapped using this syntax   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

User · Answer

I know three ways to swap variables  but a  b   b  a is the simplest  There is  XOR  for integers   x   x   y y   y   x x   x   y   Or concisely    x    y y    x x    y   Temporary variable  w   x x   y y   w del w   Tuple swap  x  y   y  x

User · Answer

That is the standard way to swap two variables  yes

User · Answer

I would not say it is a standard way to swap because it will cause some unexpected errors   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

User · Answer

You can combine tuple and XOR swaps  x  y   x   x   y  x   y   y  x  y   10  20  print  Before swapping  x    s  y    s    x y    x  y   x   x   y  x   y   y  print  After swapping  x    s  y    s    x y     or  x  y   10  20  print  Before swapping  x    s  y    s    x y    print  After swapping  x    s  y    s    x   x   y  x   y   y     Using lambda   x  y   10  20  print  Before swapping  x    s  y    s     x  y    swapper   lambda x  y     x   x   y    x   y   y    print  After swapping  x    s  y    s     swapper x  y     Output   Before swapping  x    10   y    20 After swapping  x    20   y    10

User · Answer

To get around the problems explained by eyquem  you could use the copy module to return a tuple containing  reversed  copies of the values  via a function   from copy import copy  def swapper x  y     return  copy y   copy x     Same function as a lambda   swapper   lambda x  y   copy y   copy x     Then  assign those to the desired names  like this   x  y   swapper y  x    NOTE  if you wanted to you could import use deepcopy instead of copy

User · Answer

Python evaluates expressions from left to right  Notice that while evaluating an assignment  the right-hand side is evaluated before the left-hand side  Python docs  Evaluation order  That means the following for the expression 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  The two elements are the objects designated by the identifiers b and a  that were existing before the instruction is encountered during the execution of the program  Just after the creation of this tuple  no assignment of this tuple object has still been made  but it doesn t matter  Python internally knows where it is  Then  the left-hand side is evaluated  that is to say  the tuple is assigned to the left-hand side  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 formerly b before the swap because it had name 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   This mechanism has effectively swapped the objects assigned to the identifiers a and b So  to answer your question  YES  it s the standard way to swap two identifiers on two objects  By the way  the objects are not variables  they are objects

User · Answer

Does not work for multidimensional arrays  because references are used here   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

[python] Is there a standardized method to swap two variables in Python?

XOR (for integers)

Temporary variable

Tuple swap

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