checking next element in for loop

Question

Let's say I have this array:

arr = ["foo","bar","hey"]

I can print the "foo" string with this code :

for word in arr:
    if word == "foo":
        print word

But I want also check the next word if it equals to "bar" then it should print "foobar"

How can I check the next element in a for loop?

You can get the answer you're looking for by reviewing [2395160](http://stackoverflow.com/questions/2395160/what-is-the-correct-syntax-for-else-if) — cynicaljoy, Dec 26 '15 at 19:42
@EliKorvigo: I think the OP simply wants to have access to the current and next element. — Willem Van Onsem, Dec 26 '15 at 19:42

Dan · Answer 1 · 2015-12-26T19:45:12.490

The items in a list can be referred to by their index. Using the enumerate() method to receive an iterator along with each list element (preferable to the C pattern of instantiating and incrementing your own), you can do so like this:

arr = ["foo","bar","hey"]

for i, word in enumerate(arr):
    if word == "foo" and arr[i+1] == 'bar':
        print word

However, when you get to the end of the list, you will encounter an IndexError that needs to be handled, or you can get the length (len()) of the list first and ensure i < max.

score 4 · Accepted Answer · answered Dec 26 '15 at 19:43

4

for i in range(len(arr)):
    if arr[i] == "foo":
        if arr[i+1] == 'bar':
            print arr[i] + arr[i+1]
        else:
            print arr[i]

answered Dec 26 '15 at 19:43

Anton Protopopov

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I believe the more pythonic way would be to use `enumerate()` rather than iterating based on the `len` of a list. – zayora Dec 26 '15 at 19:49
Yes, it's definitely better way to do that with `enumerate()` – Anton Protopopov Dec 26 '15 at 20:31

score 2 · Answer 3 · answered Dec 26 '15 at 19:53

Rather than check for the next value, track the previous:

last = None
for word in arr:
    if word == "foo":
        print word
    if last == 'foo' and word == 'bar':
        print 'foobar'
    last = word

Tracking what you already passed is easier than peeking ahead.

score 0 · Answer 4 · answered Dec 26 '15 at 20:22

0

You can also do it with zip:

for cur, next in zip(arr, arr[1:]):
    if nxt=='bar':
        print cur+nxt

But keep in mind that the number of iterations will be only two since len(ar[1:]) will be 2

answered Dec 26 '15 at 20:22

Iron Fist

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checking next element in for loop

4 Answers4