my code is as follows

I don't know what is wrong.

this is these changes to your code.

def purify(number):

i=0

length=len(number)-1

while i <= length:

if number[i]%2 !=0:

del number[i]

length-=1

else:

i+=1

return number

print purify([4,5,5,4])

can you please explain the purpose of this code ?

length=len(number)-1

while i <= length:

Hi,

this is to simply go through the full string.

length is equal to the length of the string (len(number) ) gives you the length including zero which is why you subtract one.

then to loop through the full string, I initiated i to equal to zero and checked that it is less than the length of the string after we check the value in the string we increase the value of I.