Patched code sample

from sqlparse.sql import Comment


def group_tokens(tlist, start_idx, end_idx):
    """Group tokens from start_idx to end_idx."""
    group_end_idx = end_idx
    for i in range(end_idx - 1, start_idx - 1, -1):
        if tlist.tokens[i].is_whitespace:
            group_end_idx -= 1
        else:
            break
    return tlist.group_tokens(Comment, start_idx, group_end_idx)


def group_comments(tlist):
    """Group comments."""
    # FIX: Use a single linear pass to group adjacent comments, which avoids
    # quadratic runtime.
    start_idx = None
    for i, token in enumerate(tlist.tokens):
        if start_idx is None and token.is_comment:
            start_idx = i
        elif start_idx is not None:
            if not (token.is_comment or token.is_whitespace):
                group_tokens(tlist, start_idx, i)
                start_idx = None

    if start_idx is not None:
        group_tokens(tlist, start_idx, len(tlist.tokens))