List append in for loop

Question

In Python  trying to do the most basic append function to a list with a loop  Not sure what i am missing here   a    for i in range 5           a a append i  a   returns   NoneType  object has no attribute  append

User · Answer

No need to re-assign   a    for i in range 5           a append i  a

User · Answer

The list append function does not return any value but None   it just adds the value to the list you are using to call that method  In the first loop round you will assign None  because the no-return of append  to a  then in the second round it will try to call a append  as a is None it will raise the Exception you are seeing You just need to change it to  a    for i in range 5           a append i  print a     0  1  2  3  4   list append is what is called a mutating or destructive method  i e  it will destroy or mutate the previous object into a new one or a new state   If you would like to create a new list based in one list without destroying or mutating it you can do something like this  a   a    b    c   result   a     d    print result     a    b    c    d    print a     a    b    c    As a corollary only  you can mimic the append method by doing the following  a   a    b    c   a   a     d    print a     a    b    c    d

User · Answer

You don t need the assignment  list append x  will always append x to a and therefore there s no need te redefine a   a      for i in range 5           a append i  print a    is all you need  This works because lists are mutable   Also see the docs on data structures

[python] List append() in for loop

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