Member Avatar for pluring

Hi!

I need to split a list if item A is followed by item B.
I'm really stuck at this and the only thing i could think of is that i should use regex, but i dont know how.

Example of list:
list =

I would like the output to be:
REF123 REF123
REF123
REF123


/Pluring

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  • Latest Post Latest Post by Namibnat

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The sample shows a flat list of emails and REF tokens being grouped so that a new group starts whenever a non-email token is immediately followed by an email token (the first output line ends at the second REF because the next item is an email). solved it with index(); correctly warned about index() returning the first match and posted a working single‑pass print loop; pointed out that join() is useful for formatting the final lines.

A cleaner, safer approach is a single pass that builds sublists (or yields groups) using an index-based lookahead and a proper email test (a simple regex rather than just checking for '@'). This avoids the index() pitfall with duplicate values and is explicit about the splitting rule:

import re

email_re = re.compile(r'^[^@\s]+@[^@\s]+\.[^@\s]+$')

def split_groups(items):
    groups = []
    cur = []
    for i, token in enumerate(items):
        cur.append(token)
        if i + 1 < len(items):
            next_tok = items[i + 1]
            if (not email_re.match(token)) and email_re.match(next_tok):
                groups.append(cur)
                cur = []
    if cur:
        groups.append(cur)
    return groups

For situations where REF tokens follow a strict naming pattern (for example REF\d+), an alternative is to join the list into a string and use a regex split with lookbehind/lookahead to cut at the space between REF and the following email. That can be compact but is more fragile if tokens contain spaces or the REF pattern changes.

Notes: prefer enumerate over list.index() for position tracking; prefer a regex for email detection instead of a bare '@' test; format final output by joining tokens of each subgroup (avoids Python2 print quirks). Test edge cases like consecutive REFs and trailing tokens.

Member Avatar for pluring

Solved it with index().

pos = list.index(i)
if "@" in list[pos + 1]:

Member Avatar for ribot

Usually you split() a string into a list.

You can join() a list into a string like this:

lst = ['email@email.com','REF']
separator = ' ' # this one space will be the string between each list element
string = separator.join( lst )
Member Avatar for Namibnat

I have been playing with it and didn't get index() to work, mainly because index always returns the first instance of the string if it occurs multiple times. I assume that normally it would be different values and then it wouldn't matter. But just in case the email is repeated somewhere in your lists, the only way I could get it to work was like this:

for a in range(len(list)):
     if '@' in list[a]: print list[a],
     else:
         if a < (len(list)-1):
             if '@' in list[a + 1]:
                 print list[a]
             else:
                 print list[a],
         else:
             print list[a]
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