Delete from a list while iterating [duplicate]

Answer 1

You should use list comprehension and zip and instead of deleting elements from a , instead take elements in a whose b value is over 15. Example -

a[:] = [i for i,j in zip(a,b) if j >=15]

We are using a[:] on the left side, so that a list object gets mutated inplace. (This is different from a = <something> as the latter simply binds name a to a new list whereas former mutates the list inplace).

---

Demo -

>>> a = [1,2,3,4,5,6,7,8,9]
>>>
>>> b = [10,11,12,13,14,15,16,17,18]
>>> a[:] = [i for i,j in zip(a,b) if j >=15]
>>> a
[6, 7, 8, 9]

Answer 2

Try using Temp list

  >>> a = [1,2,3,4,5,6,7,8,9]
  >>> b = [10,11,12,13,14,15,16,17,18]
  >>> c=[]
  >>> for i in range(0,len(b),1):
           if b[i]>=15:
                 c.append(a[i])

  >>> a=c
  >>> a
  [6, 7, 8, 9]

Answer 3

When I ran it, I didn't get an index error, but I ended up producing a = [2, 4, 6, 8]. One problem could be that as soon as you start deleting elements of a, moving left to right, its index will shift, and will no longer align with that of b. I tried counting backwards instead (and I skipped on using enumerate, as I'm a noob and I find it hard to remember how it works):

for i in range(len(b)-1,-1,-1):
    if b[i] < 15:
        del(a[i])