找到满足前2个零的nonce

def solve(block):
    import hashlib
    import json
    import copy
    b = copy.deepcopy(block)
    nonce = 0
    while True:
        b['nonce'] = nonce
        h = hashlib.sha256(json.dumps(b, sort_keys=True).encode()).hexdigest()
        if h.startswith('00'):
            print(nonce)
            break
        nonce += 1