Strange Effect of Python Assignment?












0















As we all know, for Python, we could easily assignment multiple variables in one line. But here I encounter a strange situation. Say we have a list:



x = [1, 2, 3, 4]


And then, we do



x[0], x[x[0]] = 2, 1


Finally, we would get



x = [2, 2, 3, 4]


instead of



x = [2, 1, 3, 4]


Could anyone explain what is going wrong here? How would python implement the multiple variables assignment in one line?



Thanks in advance.










share|improve this question























  • Please also check this: stackoverflow.com/questions/8725673/…

    – supl
    Nov 22 '18 at 5:34











  • So basically, Python will evaluate right-hand side of the statement (only read, no contention), and then it will assign to variables on the left-hand side from left to right. Thanks all!!

    – UserNotFound
    Nov 22 '18 at 5:42
















0















As we all know, for Python, we could easily assignment multiple variables in one line. But here I encounter a strange situation. Say we have a list:



x = [1, 2, 3, 4]


And then, we do



x[0], x[x[0]] = 2, 1


Finally, we would get



x = [2, 2, 3, 4]


instead of



x = [2, 1, 3, 4]


Could anyone explain what is going wrong here? How would python implement the multiple variables assignment in one line?



Thanks in advance.










share|improve this question























  • Please also check this: stackoverflow.com/questions/8725673/…

    – supl
    Nov 22 '18 at 5:34











  • So basically, Python will evaluate right-hand side of the statement (only read, no contention), and then it will assign to variables on the left-hand side from left to right. Thanks all!!

    – UserNotFound
    Nov 22 '18 at 5:42














0












0








0








As we all know, for Python, we could easily assignment multiple variables in one line. But here I encounter a strange situation. Say we have a list:



x = [1, 2, 3, 4]


And then, we do



x[0], x[x[0]] = 2, 1


Finally, we would get



x = [2, 2, 3, 4]


instead of



x = [2, 1, 3, 4]


Could anyone explain what is going wrong here? How would python implement the multiple variables assignment in one line?



Thanks in advance.










share|improve this question














As we all know, for Python, we could easily assignment multiple variables in one line. But here I encounter a strange situation. Say we have a list:



x = [1, 2, 3, 4]


And then, we do



x[0], x[x[0]] = 2, 1


Finally, we would get



x = [2, 2, 3, 4]


instead of



x = [2, 1, 3, 4]


Could anyone explain what is going wrong here? How would python implement the multiple variables assignment in one line?



Thanks in advance.







python syntax programming-languages






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 22 '18 at 5:21









UserNotFoundUserNotFound

11




11













  • Please also check this: stackoverflow.com/questions/8725673/…

    – supl
    Nov 22 '18 at 5:34











  • So basically, Python will evaluate right-hand side of the statement (only read, no contention), and then it will assign to variables on the left-hand side from left to right. Thanks all!!

    – UserNotFound
    Nov 22 '18 at 5:42



















  • Please also check this: stackoverflow.com/questions/8725673/…

    – supl
    Nov 22 '18 at 5:34











  • So basically, Python will evaluate right-hand side of the statement (only read, no contention), and then it will assign to variables on the left-hand side from left to right. Thanks all!!

    – UserNotFound
    Nov 22 '18 at 5:42

















Please also check this: stackoverflow.com/questions/8725673/…

– supl
Nov 22 '18 at 5:34





Please also check this: stackoverflow.com/questions/8725673/…

– supl
Nov 22 '18 at 5:34













So basically, Python will evaluate right-hand side of the statement (only read, no contention), and then it will assign to variables on the left-hand side from left to right. Thanks all!!

– UserNotFound
Nov 22 '18 at 5:42





So basically, Python will evaluate right-hand side of the statement (only read, no contention), and then it will assign to variables on the left-hand side from left to right. Thanks all!!

– UserNotFound
Nov 22 '18 at 5:42












2 Answers
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oldest

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1














The resulting list is not [2, 2, 3, 4], it's [2, 2, 1, 4]. x[0] is assigned the value 2, then x[x[0]] becomes x[2] and is assigned the value 1






share|improve this answer
























  • yes. It is [2, 2, 1, 4], Thanks!

    – UserNotFound
    Nov 22 '18 at 5:42



















0














What happens here is, python first executes your first instruction . x[0]= 2



So after 1st execution, x=[2,2,3,4]



Then it executes the 2nd one. So it changes the value of x[2]



after 2nd execution, x=[2,2,1,4]



and gives the result as [2, 2, 1, 4]






share|improve this answer























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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1














    The resulting list is not [2, 2, 3, 4], it's [2, 2, 1, 4]. x[0] is assigned the value 2, then x[x[0]] becomes x[2] and is assigned the value 1






    share|improve this answer
























    • yes. It is [2, 2, 1, 4], Thanks!

      – UserNotFound
      Nov 22 '18 at 5:42
















    1














    The resulting list is not [2, 2, 3, 4], it's [2, 2, 1, 4]. x[0] is assigned the value 2, then x[x[0]] becomes x[2] and is assigned the value 1






    share|improve this answer
























    • yes. It is [2, 2, 1, 4], Thanks!

      – UserNotFound
      Nov 22 '18 at 5:42














    1












    1








    1







    The resulting list is not [2, 2, 3, 4], it's [2, 2, 1, 4]. x[0] is assigned the value 2, then x[x[0]] becomes x[2] and is assigned the value 1






    share|improve this answer













    The resulting list is not [2, 2, 3, 4], it's [2, 2, 1, 4]. x[0] is assigned the value 2, then x[x[0]] becomes x[2] and is assigned the value 1







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered Nov 22 '18 at 5:29









    M.GM.G

    388310




    388310













    • yes. It is [2, 2, 1, 4], Thanks!

      – UserNotFound
      Nov 22 '18 at 5:42



















    • yes. It is [2, 2, 1, 4], Thanks!

      – UserNotFound
      Nov 22 '18 at 5:42

















    yes. It is [2, 2, 1, 4], Thanks!

    – UserNotFound
    Nov 22 '18 at 5:42





    yes. It is [2, 2, 1, 4], Thanks!

    – UserNotFound
    Nov 22 '18 at 5:42













    0














    What happens here is, python first executes your first instruction . x[0]= 2



    So after 1st execution, x=[2,2,3,4]



    Then it executes the 2nd one. So it changes the value of x[2]



    after 2nd execution, x=[2,2,1,4]



    and gives the result as [2, 2, 1, 4]






    share|improve this answer




























      0














      What happens here is, python first executes your first instruction . x[0]= 2



      So after 1st execution, x=[2,2,3,4]



      Then it executes the 2nd one. So it changes the value of x[2]



      after 2nd execution, x=[2,2,1,4]



      and gives the result as [2, 2, 1, 4]






      share|improve this answer


























        0












        0








        0







        What happens here is, python first executes your first instruction . x[0]= 2



        So after 1st execution, x=[2,2,3,4]



        Then it executes the 2nd one. So it changes the value of x[2]



        after 2nd execution, x=[2,2,1,4]



        and gives the result as [2, 2, 1, 4]






        share|improve this answer













        What happens here is, python first executes your first instruction . x[0]= 2



        So after 1st execution, x=[2,2,3,4]



        Then it executes the 2nd one. So it changes the value of x[2]



        after 2nd execution, x=[2,2,1,4]



        and gives the result as [2, 2, 1, 4]







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 22 '18 at 5:30









        Sandesh34Sandesh34

        254112




        254112






























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