t.py

def get_emails():
    emails = {}
    with open('list.txt', 'r') as f:
        lines = f.readlines()
    for l in lines:
        l = l.strip()
        if '@' in l:
            a, d = l.split('@')
            if d:
                if d in emails:
                    emails[d].append(a)
                else:
                    emails[d] = [a]
    return emails

# ====>

def get_emails():
    emails = {}
    with open('list.txt', 'r') as f:
        for line in f:
            line = line.strip()
            if '@' not in line:
                continue
            user, domain = l.split('@')
            if domain:
                emails.setdefault(domain, []).append(user)
    return emails