a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= []
for i in a:
if a[i] % 2 == 0 :
l.append(a[i])
The code above keeps throwing the error - "IndexError: list index out of range"
I cannot understand what to do ?
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8 Answers
When you perform for i in a you are iterating over the elements of a, not the indices!
You are trying to access: a[1] and then a[4] and then a[9] and then a[16] -> Which is the one that is causing the IndexError.
If you want to iterate only over the indices try:
>>> for i in range(len(a)):
if a[i] % 2 == 0 :
l.append(a[i])
>>> print (l)
[4, 16, 36, 64, 100]
If you need both the value and index use for index, value in enumerate(a):.
Comments
When you are iterating over a, you are looking at the value rather than the position of that value in the list.
You could use just the value like so:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= []
for val in a:
if val % 2 == 0 :
l.append(val)
Or alternately, if you need both the position and the value then you can use the enumerate function, like so:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= []
for pos, val in enumerate(a):
if a[pos] % 2 == 0 :
l.append(a[pos])
Comments
There are some ways:
for e in a:
if e % 2 == 0 :
l.append(e)
or
for i in range(len(a)):
if a[i] % 2 == 0 :
l.append(a[i])
or
for i, e in enumerate(a):
if e % 2 == 0 :
l.append(e)
or
for i, e in enumerate(a):
if a[i] % 2 == 0 :
l.append(a[i])
Comments
You could use list comprehension for that:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l = [i for i in a if i%2 == 0]
print(l)
[4, 16, 36, 64, 100]
Comments
List comprehesions can be used to make it one-liner
l=[x for x in a if x%2==0]
And as stated in ather answers your problem is that you are using list item as its indexes.
Comments
You can use filter for your task:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
print filter(lambda x: x % 2 == 0, a)
Comments
as in other answers, i takes the values from a, which are [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
in the loop when i takes the value "16", a[i] will be out of range!! (16 > len(a))
for debugging i always suggest printing...
in this case if you print the value ofi in the loop, you will find the problem yourself
Comments
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= []
for i in a:
if a[i] % 2 == 0 :
l.append(a[i])
...
if a[1] % 2 == 0:
...
if a[4] % 2 == 0:
...
if a[9] % 2 == 0:
...
if a[16] % 2 == 0:
index error, because the biggest index is 9 in array a... so u have to use this:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= []
for i in a:
if i % 2 == 0 :
l.append(i)
or this example:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= []
for i in a:
if i % 2 == 0 :
l.append(i)
or the 1 line solution:
a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
l= [x for x in a if x%2 == 0]
