问谁能告诉我IndexError到底在哪里？(Python)

EN

def gap(g, m, n):
    def is_prime(n):
        for i in range(2, n):
            if n % i == 0:
                return False
        return True
    result = []
    r = []
    primes = [p for p in range(m, n) if is_prime(p)]
    for i in range(len(primes) - 1):
        if primes[i] - primes[i + 1] == g:
            r.append(primes[i - 1])
            r.append(primes[i])
    result.append(r[0])
    result.append(r[1])
    if result == []:
        return None
    else:
        return result
print (gap(2, 100, 110))

Traceback (most recent call last):
  File "C:\Users\Harry\Documents\randompythonprograms\editable.py", line 20, in <module>
    print (gap(2, 100, 110))
  File "C:\Users\Harry\Documents\randompythonprograms\editable.py", line 14, in gap
    result.append(r[0])
IndexError: list index out of range