List index out of range, python
I have a question, that is, the 1D list looks like this:
List_A = []
and I also have another list, something like this:
List_B = [(1,2,3),(2,3,4),(3,4,5)]
Now I am trying to use:
for i in range(3):
List_A[i] = List_B[i][2]
which means I want to take every last (3rd) number from List_B to List_A but it says "index out the range" so what's the problem? Many thanks for your help.
I know the append method, but I think I can't use it because my code is in a loop, the value in List_B changes every step, something like:
List_A = []
for i in range(5):
List_B = [(i*1,i*2,i*3),(i*2,i*3,i*4),(i*3,i*4,i*5)]
for j in range(3):
List_A[j] = List_B[j][2]
that is, if I use the append method, List_A will grow to 15 items, but I need to update the value in every loop i.
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The problem is List_A
, which has only one meaning. Here you are trying to change values for indices 1
and a 2
list where none exist. So you get the error.
Use append
instead of declaring List_A
like[]
for i in range(3):
List_A.append(List_B[i][2])
This can be done in one comp-list as
List_A = [i[2] for i in List_B]
Editing messages -
Place the initialization right after the first loop
for i in range(5):
List_A = [] # Here
List_B = [(1,2,3),(2,3,4),(3,4,5)]
for j in range(3):
List_A.append(List_B[j][2])
# Do other stuff
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This cycle is a problem
for i in range(3):
List_A[i] = List_B[i][2]
You can only access List_A[0]
, the rest of the values i
are out of range. If you are trying to populate a list you should useappend
List_A = []
for i in range(3):
List_A.append(List_B[i][2])
Or more Pythonic uses a list comprehension
List_A = [i[2] for i in List_B]
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