Why does this iterative list-growing code give IndexError list assignment index out of range

Question

Please consider the following code   i    1  2  3  5  8  13  j      k   0  for l in i      j k    l     k    1  print j   The output  Python 2 6 6 on Win 7 32-bit  is    gt  Traceback  most recent call last     gt      j k    l IndexError  list assignment index out of range   I guess it s something simple I don t understand  Can someone clear it up

User · Answer

Maybe you need extend    i  1 3 5 7  j    j extend i

User · Answer

You could also use a list comprehension   j    l for l in i    or make a copy of it using the statement   j   i

User · Answer

One more way    j i 0  for k in range 1 len i        j   numpy vstack  j i k      In this case j will be a numpy array

User · Answer

j append l    Also avoid using lower-case  L s  because it is easy for them to be confused with 1 s

User · Answer

j is an empty list  but you re attempting to write to element  0  in the first iteration  which doesn t exist yet   Try the following instead  to add a new element to the end of the list   for l in i      j append l    Of course  you d never do this in practice if all you wanted to do was to copy an existing list  You d just do   j   list i    Alternatively  if you wanted to use the Python list like an array in other languages  then you could pre-create a list with its elements set to a null value  None in the example below   and later  overwrite the values in specific positions   i    1  2  3  5  8  13  j    None    len i   j     None  None  None  None  None  None  k   0  for l in i     j k    l    k    1   The thing to realise is that a list object will not allow you to assign a value to an index that doesn t exist

User · Answer

Do j append l  instead of j k    l and avoid k at all

User · Answer

Your other option is to initialize j   j    None    len i

User · Answer

I think the Python method insert is what you re looking for   Inserts element x at position i  list insert i x   array    1 2 3 4 5   array insert 1 20   print array     prints  1 2 20 3 4 5

User · Answer

You could use a dictionary  similar to an associative array  for j i    1  2  3  5  8  13  j       initiate as dictionary k   0  for l in i      j k    l     k    1  print j   will print    0  1  1  2  2  3  3  5  4  8  5  13

[python] Why does this iterative list-growing code give IndexError: list assignment index out of range?

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