Python调用testBlock类方法时即使使用self仍报NameError如何解决

核心错误原因 #

• 方法调用范围错误：testBlock是Block类内部定义的成员方法，不能直接在全局作用域调用，这是你触发NameError的直接原因。C++中类的非静态成员方法也需要先实例化对象才能调用，Python逻辑一致。
• 拼写不匹配问题：代码中存在多处方法名拼写不一致：
  • __init__中调用了不存在的self.hash_blockhash()
  • 方法定义为hash_black()，但调用时写的是blockHash.hash_block()
• 语法使用错误：
  • hashlib的hexdigest是可调用方法，必须加括号执行，否则返回的是方法对象而非哈希字符串
  • 你给prev_blockhash传的是hashlib.sha256实例对象，直接转字符串不会得到哈希值，需要先调用hexdigest()获取结果
• 传参逻辑错误：给testBlock加self后，你创建Block实例时取的是当前对象的属性值，而非传入的参数，完全不符合预期。

修复方案 #

这里提供两种修复路径，你可以按需选择：

方案1：将testBlock改为全局独立函数（最贴合你当前使用逻辑） #

import hashlib

class Block():
    def __init__(self, height = 0, timestamp = "", tx = "", nonce = 0, prev_blockhash = "", curr_blockhash = ""):
        self.height = height
        self.timestamp = timestamp
        self.tx = tx
        self.nonce = nonce
        self.prev_blockhash = prev_blockhash
        self.curr_blockhash = self.hash_block() # 修正方法名
    def hash_block(self): # 统一方法名
        returning = hashlib.sha256()
        neoHeight = str(self.height)
        neoTimestamp = str(self.timestamp)
        neoTx = str(self.tx)
        neoNonce = str(self.nonce)
        neoPrev_blockhash = str(self.prev_blockhash)
        all_str = (neoHeight + neoTimestamp + neoTx + neoNonce + neoPrev_blockhash)
        all_bytes = all_str.encode()
        returning.update(all_bytes)
        hashed = returning.hexdigest() # 加括号执行方法
        return hashed

# 移到类外作为全局函数
def testBlock(height, timestamp, tx, nonce, prev_blockhash):
    blockHash = Block(height, timestamp, tx, nonce, prev_blockhash)
    blockHashed = blockHash.hash_block()
    print('Block Hashed:')
    print(blockHashed)
    return blockHashed

height = 0
timestamp = '2021-02-25 11:59:59.134365'
tx = 'Alice, Bob, 10'
nonce = 0
prev_blockhash = hashlib.sha256()
prev_blockhash.update(b'0')
prev_blockhash = prev_blockhash.hexdigest() # 提前拿到哈希字符串

target_hash = "e2169844b4dbb8a35b15c5da2cd1cccbeb873da319bf5f3983b15b5fb76bafa7"

# 现在可以正常调用，不会触发NameError
result_hash = testBlock(height, timestamp, tx, nonce, prev_blockhash)
assert result_hash
# 如果你要验证和目标哈希一致可以用：assert result_hash == target_hash

方案2：将testBlock声明为类的静态方法（保留在类内的结构） #

如果要保留testBlock在Block类内部，可以用@staticmethod装饰器声明为静态方法，不需要self参数：

import hashlib

class Block():
    def __init__(self, height = 0, timestamp = "", tx = "", nonce = 0, prev_blockhash = "", curr_blockhash = ""):
        self.height = height
        self.timestamp = timestamp
        self.tx = tx
        self.nonce = nonce
        self.prev_blockhash = prev_blockhash
        self.curr_blockhash = self.hash_block()
    def hash_block(self):
        returning = hashlib.sha256()
        neoHeight = str(self.height)
        neoTimestamp = str(self.timestamp)
        neoTx = str(self.tx)
        neoNonce = str(self.nonce)
        neoPrev_blockhash = str(self.prev_blockhash)
        all_str = (neoHeight + neoTimestamp + neoTx + neoNonce + neoPrev_blockhash)
        all_bytes = all_str.encode()
        returning.update(all_bytes)
        hashed = returning.hexdigest()
        return hashed
    
    @staticmethod
    def testBlock(height, timestamp, tx, nonce, prev_blockhash):
        blockHash = Block(height, timestamp, tx, nonce, prev_blockhash)
        blockHashed = blockHash.hash_block()
        print('Block Hashed:')
        print(blockHashed)
        return blockHashed

height = 0
timestamp = '2021-02-25 11:59:59.134365'
tx = 'Alice, Bob, 10'
nonce = 0
prev_blockhash = hashlib.sha256()
prev_blockhash.update(b'0')
prev_blockhash = prev_blockhash.hexdigest()

# 调用时需要加类名前缀
result_hash = Block.testBlock(height, timestamp, tx, nonce, prev_blockhash)
assert result_hash

内容的提问来源于stack exchange，提问作者user16919308