Look for item inside list, when found, inside same item before it. (python)

Question

inside a list I'm looking for the item '-', when we find it, I want to insert '-' before it. Should be pretty easy but I'm struggling :S

Answer 1

Use the list.insert and list.index methods. index gives you the index of the item you're looking for, insert does what it says it does:

l = ['a', 1, '-', 2] # random list
l.insert(l.index('-'), '-')
print(l)

Reacting to your comment: If you have more than one occurence, it works a bit less elegantly:

l = ["a", 1, "-", 2, "-", 2, 5, "-"]
# get indices of '-'
idxs = [i for i, c in enumerate(l) if c == "-"]
# loop over indices and insert, account for already added items
for i, idx in enumerate(idxs):
    l.insert(idx + i, "-")