对于问题的第一部分，将a作为列表传递:

For the first part of your question, pass a as a list:

def random_dna_sequence(length):
    return ''.join(np.random.choice(list('ACTG')) for _ in range(length))

或将您的碱基定义为列表或元组:

Or define your bases as a list or tuple:

BASES = ('A', 'C', 'T', 'G')

def random_dna_sequence(length):
    return ''.join(np.random.choice(BASES) for _ in range(length))

第二部分有一个类似的解决方案:将概率作为列表或元组传递:

The second part has a similar solution: pass the probabilities as a list or tuple:

BASES = ('A', 'C', 'T', 'G')
P = (0.2, 0.2, 0.3, 0.3)

def random_dna_sequence(length):
    return ''.join(np.random.choice(BASES, p=P) for _ in range(length))